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The Yecoro wheat (right) cultivar is sensitive to salinity, plants resulting from a hybrid cross with cultivar W4910 (left) show greater tolerance to high salinity

Plant breeding is the science of changing the traits of plants in order to produce desired characteristics.[1] It is used to improve the quality of plant products for use by humans and animals.[2] The goals of plant breeding are to produce crop varieties that boast unique and superior traits for a variety of applications. The most frequently addressed agricultural traits are those related to biotic and abiotic stress tolerance, grain or biomass yield, end-use quality characteristics such as taste or the concentrations of specific biological molecules (proteins, sugars, lipids, vitamins, fibers) and ease of processing (harvesting, milling, baking, malting, blending, etc.).[3]

Plant breeding can be performed using many different techniques, ranging from the selection of the most desirable plants for propagation, to methods that make use of knowledge of genetics and chromosomes, to more complex molecular techniques. Genes in a plant are what determine what type of qualitative or quantitative traits it will have. Plant breeders strive to create a specific outcome of plants and potentially new plant varieties,[2] and in the course of doing so, narrow down the genetic diversity of that variety to a specific few biotypes.[4]

It is practiced worldwide by individuals such as gardeners and farmers, and by professional plant breeders employed by organizations such as government institutions, universities, crop-specific industry associations or research centers. International development agencies believe that breeding new crops is important for ensuring food security by developing new varieties that are higher yielding, disease resistant, drought tolerant or regionally adapted to different environments and growing conditions.[5]

A 2023 study shows that without plant breeding, Europe would have produced 20% fewer arable crops over the last 20 years, consuming an additional 21.6 million hectares (53 million acres) of land and emitting 4 billion tonnes (3.9×109 long tons; 4.4×109 short tons) of carbon.[6][7] Wheat species created for Morocco are currently being crossed with plants to create new varieties for northern France. Soy beans, which were previously grown predominantly in the south of France, are now grown in southern Germany.[6][8]

History

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Main article: History of plant breeding

Plant breeding started with sedentary agriculture and particularly the domestication of the first agricultural plants, a practice which is estimated to date back 9,000 to 11,000 years.[9] Initially early farmers simply selected food plants with particular desirable characteristics, and employed these as progenitors for subsequent generations, resulting in an accumulation of valuable traits over time.

Grafting technology had been practiced in China before 2000 BCE.[10]

By 500 BCE grafting was well established and practiced.[11]

Gregor Mendel (1822–84) is considered the "father of genetics". His experiments with plant hybridization led to his establishing laws of inheritance. Genetics stimulated research to improve crop production through plant breeding.

Selective breeding played a crucial role in the Green Revolution of the 20th century.

Modern plant breeding is applied genetics, but its scientific basis is broader, covering molecular biology, cytology, systematics, physiology, pathology, entomology, chemistry, and statistics (biometrics). It has also developed its own technology.

Classical plant breeding

[edit]
For the role of crossing and plant breeding in viticulture, see Propagation of grapevines.
Selective breeding enlarged desired traits of the wild cabbage plant (Brassica oleracea) over hundreds of years, resulting in dozens of today's agricultural crops. Cabbage, kale, broccoli, and cauliflower are all cultivars of this plant.

One major technique of plant breeding is selection, the process of selectively propagating plants with desirable characteristics and eliminating or "culling" those with less desirable characteristics.[12]

Another technique is the deliberate interbreeding (crossing) of closely or distantly related individuals to produce new crop varieties or lines with desirable properties. Plants are crossbred to introduce traits/genes from one variety or line into a new genetic background. For example, a mildew-resistant pea may be crossed with a high-yielding but susceptible pea, the goal of the cross being to introduce mildew resistance without losing the high-yield characteristics. Progeny from the cross would then be crossed with the high-yielding parent to ensure that the progeny were most like the high-yielding parent, (backcrossing). The progeny from that cross would then be tested for yield (selection, as described above) and mildew resistance and high-yielding resistant plants would be further developed. Plants may also be crossed with themselves to produce inbred varieties for breeding. Pollinators may be excluded through the use of pollination bags.

Classical breeding relies largely on homologous recombination between chromosomes to generate genetic diversity. The classical plant breeder may also make use of a number of in vitro techniques such as protoplast fusion, embryo rescue or mutagenesis (see below) to generate diversity and produce hybrid plants that would not exist in nature.

Traits that breeders have tried to incorporate into crop plants include:

  1. Improved quality, such as increased nutrition, improved flavor, or greater beauty
  2. Increased yield of the crop
  3. Increased tolerance of environmental pressures (salinity, extreme temperature, drought)
  4. Resistance to viruses, fungi and bacteria
  5. Increased tolerance to insect pests
  6. Increased tolerance of herbicides
  7. Longer storage period for the harvested crop

Before World War II

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Garton's catalogue from 1902

Gartons Agricultural Plant Breeders in England was established in 1880, which became a public company in 1898, by John Garton, who was one of the first to commercialize new varieties of agricultural crops created through cross-pollination.[13] The firm's first introduction was the Abundance Oat, an oat variety.[14][15] It is one of the first agricultural grain varieties bred from a controlled cross, introduced to commerce in 1892.[14][15]

In the early 20th century, plant breeders realized that Gregor Mendel's findings on the non-random nature of inheritance could be applied to seedling populations produced through deliberate pollinations to predict the frequencies of different types. Wheat hybrids were bred to increase the crop production of Italy during the so-called "Battle for Grain" (1925–1940). Heterosis was explained by George Harrison Shull. It describes the tendency of the progeny of a specific cross to outperform both parents. The detection of the usefulness of heterosis for plant breeding has led to the development of inbred lines that reveal a heterotic yield advantage when they are crossed. Maize was the first species where heterosis was widely used to produce hybrids.

Statistical methods were also developed to analyze gene action and distinguish heritable variation from variation caused by environment. In 1933 another important breeding technique, cytoplasmic male sterility (CMS), developed in maize, was described by Marcus Morton Rhoades. CMS is a maternally inherited trait that makes the plant produce sterile pollen. This enables the production of hybrids without the need for labor-intensive detasseling.

These early breeding techniques resulted in large yield increase in the United States in the early 20th century. Similar yield increases were not produced elsewhere until after World War II, the Green Revolution increased crop production in the developing world in the 1960s.

After World War II

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In vitro-culture of Vitis (grapevine), Geisenheim Grape Breeding Institute

Following World War II a number of techniques were developed that allowed plant breeders to hybridize distantly related species, and artificially induce genetic diversity.

When distantly related species are crossed, plant breeders make use of a number of plant tissue culture techniques to produce progeny from otherwise fruitless mating. Interspecific and intergeneric hybrids are produced from a cross of related species or genera that do not normally sexually reproduce with each other. These crosses are referred to as Wide crosses. For example, the cereal triticale is a wheat and rye hybrid. The cells in the plants derived from the first generation created from the cross contained an uneven number of chromosomes and as a result was sterile. The cell division inhibitor colchicine was used to double the number of chromosomes in the cell and thus allow the production of a fertile line.

Failure to produce a hybrid may be due to pre- or post-fertilization incompatibility. If fertilization is possible between two species or genera, the hybrid embryo may abort before maturation. If this does occur the embryo resulting from an interspecific or intergeneric cross can sometimes be rescued and cultured to produce a whole plant. Such a method is referred to as embryo rescue. This technique has been used to produce new rice for Africa, an interspecific cross of Asian rice Oryza sativa and African rice O. glaberrima.

Hybrids may also be produced by a technique called protoplast fusion. In this case protoplasts are fused, usually in an electric field. Viable recombinants can be regenerated in culture.

Chemical mutagens like ethyl methanesulfonate (EMS) and dimethyl sulfate (DMS), radiation, and transposons are used for mutagenesis. Mutagenesis is the generation of mutants. The breeder hopes for desirable traits to be bred with other cultivars – a process known as mutation breeding. Classical plant breeders also generate genetic diversity within a species by exploiting a process called somaclonal variation, which occurs in plants produced from tissue culture, particularly plants derived from callus. Induced polyploidy, and the addition or removal of chromosomes using a technique called chromosome engineering may also be used.

Agricultural research on potato plants

When a desirable trait has been bred into a species, a number of crosses to the favored parent are made to make the new plant as similar to the favored parent as possible. Returning to the example of the mildew resistant pea being crossed with a high-yielding but susceptible pea, to make the mildew resistant progeny of the cross most like the high-yielding parent, the progeny will be crossed back to that parent for several generations (See backcrossing). This process removes most of the genetic contribution of the mildew resistant parent. Classical breeding is therefore a cyclical process.[clarification needed]

With classical breeding techniques, the breeder does not know exactly what genes have been introduced to the new cultivars. Some scientists therefore argue that plants produced by classical breeding methods should undergo the same safety testing regime as genetically modified plants. There have been instances where plants bred using classical techniques have been unsuitable for human consumption, for example the poison solanine was unintentionally increased to unacceptable levels in certain varieties of potato through plant breeding. New potato varieties are often screened for solanine levels before reaching the marketplace.[citation needed]

Even with the very latest in biotech-assisted conventional breeding, incorporation of a trait takes an average of seven generations for clonally propagated crops, nine for self-fertilising, and seventeen for cross-pollinating.[16][17]

Modern plant breeding

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See also: New Breeding Techniques

Modern plant breeding may use techniques of molecular biology to select, or in the case of genetic modification, to insert, desirable traits into plants. Application of biotechnology or molecular biology is also known as molecular breeding.

Modern facilities in molecular biology are now used in plant breeding.

Marker assisted selection

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Main article: Marker assisted selection

Sometimes many different genes can influence a desirable trait in plant breeding. The use of tools such as molecular markers or DNA fingerprinting can map thousands of genes. This allows plant breeders to screen large populations of plants for those that possess the trait of interest. The screening is based on the presence or absence of a certain gene as determined by laboratory procedures, rather than on the visual identification of the expressed trait in the plant. The purpose of marker assisted selection, or plant genome analysis, is to identify the location and function (phenotype) of various genes within the genome. If all of the genes are identified it leads to genome sequence.[citation needed][clarification needed] All plants have varying sizes and lengths of genomes with genes that code for different proteins, but many are also the same. If a gene's location and function is identified in one plant species, a very similar gene likely can also be found in a similar location in another related species genome.[18]

Doubled haploidy and reverse breeding

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Main article: Doubled haploidy

Homozygous plants with desirable traits can be produced from heterozygous starting plants, if a haploid cell with the alleles for those traits can be produced, and then used to make a doubled haploid. The doubled haploid will be homozygous for the desired traits. Furthermore, two different homozygous plants created in that way can be used to produce a generation of F1 hybrid plants which have the advantages of heterozygosity and a greater range of possible traits. Thus, an individual heterozygous plant chosen for its desirable characteristics can be converted into a heterozygous variety (F1 hybrid) without the necessity of vegetative reproduction but as the result of the cross of two homozygous/doubled haploid lines derived from the originally selected plant.[19] This shortcut has been dubbed 'reverse breeding'.[20] Plant tissue culturing can produce haploid or double haploid plant lines and generations. This cuts down the genetic diversity taken from that plant species in order to select for desirable traits that will increase the fitness of the individuals. Using this method decreases the need for breeding multiple generations of plants to get a generation that is homogeneous for the desired traits, thereby saving much time over the natural version of the same process. There are many plant tissue culturing techniques that can be used to achieve haploid plants, but microspore culturing is currently the most promising for producing the largest numbers of them.[18]

Genetic modification

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Main article: Transgenic plants

Genetic modification of plants is achieved by adding a specific gene or genes to a plant, or by knocking down a gene with RNAi, to produce a desirable phenotype. The plants resulting from adding a gene are often referred to as transgenic plants. If for genetic modification genes of the species or of a crossable plant are used under control of their native promoter, then they are called cisgenic plants. Sometimes genetic modification can produce a plant with the desired trait or traits faster than classical breeding because the majority of the plant's genome is not altered.

To genetically modify a plant, a genetic construct must be designed so that the gene to be added or removed will be expressed by the plant. To do this, a promoter to drive transcription and a termination sequence to stop transcription of the new gene, and the gene or genes of interest must be introduced to the plant. A marker for the selection of transformed plants is also included. In the laboratory, antibiotic resistance is a commonly used marker: Plants that have been successfully transformed will grow on media containing antibiotics; plants that have not been transformed will die. In some instances markers for selection are removed by backcrossing with the parent plant prior to commercial release.

The construct can be inserted in the plant genome by genetic recombination using the bacteria Agrobacterium tumefaciens or A. rhizogenes, or by direct methods like the gene gun or microinjection. Using plant viruses to insert genetic constructs into plants is also a possibility, but the technique is limited by the host range of the virus. For example, Cauliflower mosaic virus (CaMV) only infects cauliflower and related species. Another limitation of viral vectors is that the virus is not usually passed on to the progeny, so every plant has to be inoculated.

The majority of commercially released transgenic plants are currently limited to plants that have introduced resistance to insect pests and herbicides. Insect resistance is achieved through incorporation of a gene from Bacillus thuringiensis (Bt) that encodes a protein that is toxic to some insects. For example, the cotton bollworm, a common cotton pest, feeds on Bt cotton it will ingest the toxin and die. Herbicides usually work by binding to certain plant enzymes and inhibiting their action.[21] The enzymes that the herbicide inhibits are known as the herbicide's "target site". Herbicide resistance can be engineered into crops by expressing a version of target site protein that is not inhibited by the herbicide. This is the method used to produce glyphosate resistant ("Roundup Ready") crop plants.

Genetic modification can further increase yields by increasing stress tolerance to a given environment. Stresses such as temperature variation, are signalled to the plant via a cascade of signalling molecules which will activate a transcription factor to regulate gene expression. Overexpression of particular genes involved in cold acclimation has been shown to produce more resistance to freezing, which is one common cause of yield loss[22]

Genetic modification of plants that can produce pharmaceuticals (and industrial chemicals), sometimes called pharming, is a rather radical new area of plant breeding.[23]

The debate surrounding genetically modified food during the 1990s peaked in 1999 in terms of media coverage and risk perception,[24] and continues today – for example, "Germany has thrown its weight behind a growing European mutiny over genetically modified crops by banning the planting of a widely grown pest-resistant corn variety."[25] The debate encompasses the ecological impact of genetically modified plants, the safety of genetically modified food and concepts used for safety evaluation like substantial equivalence. Such concerns are not new to plant breeding. Most countries have regulatory processes in place to help ensure that new crop varieties entering the marketplace are both safe and meet farmers' needs. Examples include variety registration, seed schemes, regulatory authorizations for GM plants, etc.

Breeding and the microbiome

[edit]

Industrial breeding of plants has unintentionally altered how agricultural cultivars associate with their microbiome.[26] In maize, for example, breeding has altered the nitrogen cycling taxa required to the rhizosphere, with more modern lines recruiting less nitrogen fixing taxa and more nitrifiers and denitrifiers.[27] Microbiomes of breeding lines showed that hybrid plants share much of their bacterial community with their parents, such as Cucurbita seeds and apple shoot endophytes.[28][29][30] In addition, the proportional contribution of the microbiome from parents to offspring corresponds to the amount of genetic material contributed by each parent during breeding and domestication.[30]

Phenotyping and artificial intelligence

[edit]

As of 2020 machine learning – and especially deep machine learning – has recently become more commonly used in phenotyping. Computer vision using ML has made great strides and is now being applied to leaf phenotyping and other phenotyping jobs typically performed by human eyes. Pound et al. 2017 and Singh et al. 2016 are especially salient examples of early successful application and demonstration of the general usability of the process across multiple target plant species. These methods will work even better with large, publicly available open data sets.[31]

Speed breeding

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Speed breeding is introduced by Watson et al. 2018. Classical (human performed) phenotyping during speed breeding is also possible, using a procedure developed by Richard et al. 2015. As of 2020 it is highly anticipated that SB and automated phenotyping will, combined, produce greatly improved outcomes – see § Phenotyping and artificial intelligence above.[31]

Genomic selection (GS)

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The NGS platform has substantially declined the time and cost required for sequencing and facilitated SNP discovery in model and non-model plants. This in turn has led to employing large-scale SNP markers in genomic selection approaches which aim at predicting genomic breeding values/GEBVs of genotypes in a given population. This method can increase the selection accuracy and decrease the time of each breeding cycle. It has been used in different crops such as maize, wheat, etc.[32][33]

Participatory plant breeding

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Participatory plant breeding (PPB) is when farmers are involved in a crop improvement programme with opportunities to make decisions and contribute to the research process at different stages.[34][35][36] Participatory approaches to crop improvement can also be applied when plant biotechnologies are being used for crop improvement.[37] Local agricultural systems and genetic diversity are strengthened by participatory programs, and outcomes are enhanced by farmers knowledge of the quality required and evaluation of the target environment.[38]

A 2019 review of participatory plant breeding indicated that it had not gained widespread acceptance despite its record of successfully developing varieties with improved diversity and nutritional quality, as well as greater likelihood of these improved varieties being adopted by farmers. This review also found participatory plant breeding to have a better cost/benefit ratio than non-participatory approaches, and suggested incorporating participatory plant breeding with evolutionary plant breeding.[39]

Evolutionary plant breeding

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See also: Landrace § Plant_landrace_development

Evolutionary plant breeding describes practices which use mass populations with diverse genotypes grown under competitive natural selection. Survival in common crop cultivation environments is the predominant method of selection, rather than direct selection by growers and breeders. Individual plants that are favored under prevailing growing conditions, such as environment and inputs, contribute more seed to the next generation than less-adapted individuals.[40] Evolutionary plant breeding has been successfully used by the Nepal National Gene Bank to preserve landrace diversity within Jumli Marshi rice while reducing its susceptibility to blast disease. These practices have also been used in Nepal with bean landraces.[41]

In 1929, Harlan and Martini proposed a method of plant breeding with heterogeneous populations by pooling an equal number of F2 seeds obtained from 378 crosses among 28 geographically diverse barley cultivars. In 1938, Harlan and Martini demonstrated evolution by natural selection in mixed dynamic populations as a few varieties that became dominant in some locations almost disappeared in others; poorly-adapted varieties disappeared everywhere.[42]

Evolutionary breeding populations have been used to establish self-regulating plant–pathogen systems. Examples include barley, where breeders were able to improve resistance to Rynchosporium secalis scald over 45 generations.[43] An evolutionary breeding project grew F5 hybrid bulk soybean populations on soil infested by the soybean cyst nematode and was able to increase the proportion of resistant plants from 5% to 40%. The International Center for Agricultural Research in the Dry Areas (ICARDA) evolutionary plant breeding is combined with participatory plant breeding in order to allow farmers to choose which varieties suit their needs in their local environment.[43]

An influential 1956 effort by Coit A. Suneson to codify this approach coined the term evolutionary plant breeding and concluded that 15 generations of natural selection are desirable to produce results that are competitive with conventional breeding.[44] Evolutionary breeding allows working with much larger plant population sizes than conventional breeding.[42] It has also been used in tandem with conventional practices in order to develop both heterogeneous and homogeneous crop lines for low input agricultural systems that have unpredictable stress conditions.[45]

Evolutionary plant breeding has been delineated into four stages:[40]

  • Stage 1: Genetic diversity is created, for example by manual crosses of inbreeding species or mixing of cultivars in outcrossing species.
  • Stage 2: Multiplication of seeds
  • Stage 3: Seeds of each cross are then mixed to produce the first generation of the Composite Cross Population (CCP). The entire offspring is sown to grow and set seed. As the number of plants in the population increases, a proportion of the harvested seed is saved for sowing.
  • Stage 4: The seed can be used for continued evolutionary plant breeding or as a starting point for a conventional breeding effort.

Issues and concerns

[edit]

Breeding and food security

[edit]

Issues facing plant breeding in the future include the lack of arable land, increasingly harsh cropping conditions and the need to maintain food security, which involves being able to provide the world population with sufficient nutrition. Crops need to be able to mature in multiple environments to allow worldwide access, which involves solving problems including drought tolerance. It has been suggested that global solutions are achievable through the process of plant breeding, with its ability to select specific genes allowing crops to perform at a level which yields the desired results.[46] One issue facing agriculture is the loss of landraces and other local varieties which have diversity that may have useful genes for climate adaptation in the future.[43]

Conventional breeding intentionally limits phenotype plasticity within genotypes and limits variability between genotypes.[45] Uniformity does not allow crops to adapt to climate change and other biotic stresses and abiotic stresses.[43]

Plant breeders' rights

[edit]

Plant breeders' rights is an important and controversial issue. Production of new varieties is dominated by commercial plant breeders, who seek to protect their work and collect royalties through national and international agreements based in intellectual property rights. The range of related issues is complex. In the simplest terms, critics of the increasingly restrictive regulations argue that, through a combination of technical and economic pressures, commercial breeders are reducing biodiversity and significantly constraining individuals (such as farmers) from developing and trading seed on a regional level.[47] Efforts to strengthen breeders' rights, for example, by lengthening periods of variety protection, are ongoing.[citation needed]

Intellectual property legislation for plants often uses definitions that typically include genetic uniformity and unchanging appearance over generations. These legal definitions of stability contrast with traditional agronomic usage, which considers stability in terms of how consistent the yield or quality of a crop remains across locations and over time.[40]

As of 2020, regulations in Nepal only allow uniform varieties to be registered or released. Evolutionary plant populations and many landraces are polymorphic and do not meet these standards.[41]

Environmental stressors

[edit]

Uniform and genetically stable cultivars can be inadequate for dealing with environmental fluctuations and novel stress factors.[40] Plant breeders have focused on identifying crops which will ensure crops perform under these conditions; a way to achieve this is finding strains of the crop that is resistance to drought conditions with low nitrogen. It is evident from this that plant breeding is vital for future agriculture to survive as it enables farmers to produce stress resistant crops hence improving food security.[48] In countries that experience harsh winters such as Iceland, Germany and further east in Europe, plant breeders are involved in breeding for tolerance to frost, continuous snow-cover, frost-drought (desiccation from wind and solar radiation under frost) and high moisture levels in soil in winter.[49]

Long-term process

[edit]

Breeding is not a quick process, which is especially important when breeding to ameliorate a disease. The average time from human recognition of a new fungal disease threat to the release of a resistant crop for that pathogen is at least twelve years.[17][50]

Maintaining specific conditions

[edit]

When new plant breeds or cultivars are bred, they must be maintained and propagated. Some plants are propagated by asexual means while others are propagated by seeds. Seed propagated cultivars require specific control over seed source and production procedures to maintain the integrity of the plant breeds results. Isolation is necessary to prevent cross contamination with related plants or the mixing of seeds after harvesting. Isolation is normally accomplished by planting distance but in certain crops, plants are enclosed in greenhouses or cages (most commonly used when producing F1 hybrids).

Nutritional value

[edit]

Modern plant breeding, whether classical or through genetic engineering, comes with issues of concern, particularly with regard to food crops. The question of whether breeding can have a negative effect on nutritional value is central in this respect. Although relatively little direct research in this area has been done, there are scientific indications that, by favoring certain aspects of a plant's development, other aspects may be retarded. A study published in the Journal of the American College of Nutrition in 2004, entitled Changes in USDA Food Composition Data for 43 Garden Crops, 1950 to 1999, compared nutritional analysis of vegetables done in 1950 and in 1999, and found substantial decreases in six of 13 nutrients measured, including 6% of protein and 38% of riboflavin. Reductions in calcium, phosphorus, iron and ascorbic acid were also found. The study, conducted at the Biochemical Institute, University of Texas at Austin, concluded in summary: "We suggest that any real declines are generally most easily explained by changes in cultivated varieties between 1950 and 1999, in which there may be trade-offs between yield and nutrient content."[51]

Plant breeding can contribute to global food security as it is a cost-effective tool for increasing nutritional value of forage and crops. Improvements in nutritional value for forage crops from the use of analytical chemistry and rumen fermentation technology have been recorded since 1960; this science and technology gave breeders the ability to screen thousands of samples within a small amount of time, meaning breeders could identify a high performing hybrid quicker. The genetic improvement was mainly in vitro dry matter digestibility (IVDMD) resulting in 0.7-2.5% increase, at just 1% increase in IVDMD a single Bos Taurus also known as beef cattle reported 3.2% increase in daily gains. This improvement indicates plant breeding is an essential tool in gearing future agriculture to perform at a more advanced level. [52]

Yield

[edit]

With an increasing population, the production of food needs to increase with it. It is estimated that a 70% increase in food production is needed by 2050 in order to meet the Declaration of the World Summit on Food Security. But with the degradation of agricultural land, simply planting more crops is no longer a viable option. New varieties of plants can in some cases be developed through plant breeding that generate an increase of yield without relying on an increase in land area. An example of this can be seen in Asia, where food production per capita has increased twofold. This has been achieved through not only the use of fertilisers, but through the use of better crops that have been specifically designed for the area.[53][54]

Role of plant breeding in organic agriculture

[edit]

Some critics of organic agriculture claim it is too low-yielding to be a viable alternative to conventional agriculture in situations when that poor performance may be the result in part of growing poorly-adapted varieties.[55][56] It is estimated that over 95% of organic agriculture is based on conventionally adapted varieties, even though the production environments found in organic vs. conventional farming systems are vastly different due to their distinctive management practices.[56] Most notably, organic farmers have fewer inputs available than conventional growers to control their production environments. Breeding varieties specifically adapted to the unique conditions of organic agriculture is critical for this sector to realize its full potential. This requires selection for traits such as:[56]

  • Water use efficiency
  • Nutrient use efficiency (particularly nitrogen and phosphorus)
  • Weed competitiveness
  • Tolerance of mechanical weed control
  • Pest/disease resistance
  • Early maturity (as a mechanism for avoidance of particular stresses)
  • Abiotic stress tolerance (i.e. drought, salinity, etc...)

Currently, few breeding programs are directed at organic agriculture and until recently those that did address this sector have generally relied on indirect selection (i.e. selection in conventional environments for traits considered important for organic agriculture). However, because the difference between organic and conventional environments is large, a given genotype may perform very differently in each environment due to an interaction between genes and the environment (see gene–environment interaction). If this interaction is severe enough, an important trait required for the organic environment may not be revealed in the conventional environment, which can result in the selection of poorly adapted individuals.[55] To ensure the most adapted varieties are identified, advocates of organic breeding now promote the use of direct selection (i.e. selection in the target environment) for many agronomic traits.

There are many classical and modern breeding techniques that can be utilized for crop improvement in organic agriculture despite the ban on genetically modified organisms. For instance, controlled crosses between individuals allow desirable genetic variation to be recombined and transferred to seed progeny via natural processes. Marker assisted selection can also be employed as a diagnostics tool to facilitate selection of progeny who possess the desired trait(s), greatly speeding up the breeding process.[57] This technique has proven particularly useful for the introgression of resistance genes into new backgrounds, as well as the efficient selection of many resistance genes pyramided into a single individual. Molecular markers are not currently available for many important traits, especially complex ones controlled by many genes.

List of notable plant breeders

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See also

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References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Plant breeding

View on Grokipedia
from Grokipedia
Plant breeding is the and practice of inducing heritable changes in plants to enhance desirable traits such as yield, , resistance, and to abiotic stresses through methods including selection, hybridization, and genetic modification. This process, rooted in empirical observation and causal mechanisms of , has transformed by systematically exploiting to meet human needs, from ancient to modern high-throughput breeding programs. Key achievements include the tripling of U.S. yields per acre from about 13 bushels in 1888 to 45 bushels by 2018, driven largely by breeding innovations, and the Green Revolution's introduction of semi-dwarf varieties that doubled or tripled and outputs in developing regions through the and 1970s. These gains, averaging around 1% annual yield increases in major cereals attributable to improved varieties, underscore plant breeding's causal role in averting famines and supporting , though challenges persist in sustaining amid variability and genetic bottlenecks. Contemporary techniques, such as genomic selection and CRISPR-based editing, build on first principles of to accelerate genetic gains, enabling precise trait stacking without reliance on broad , while confirms their efficacy in boosting productivity beyond conventional limits.

History

Pre-Mendelian Practices

Pre-Mendelian plant breeding encompassed empirical methods centered on selection and vegetative propagation, originating with the of wild species during the approximately 10,000 years ago. Early agriculturalists in regions like the selected seeds from wild progenitors exhibiting favorable traits, such as larger seeds or easier harvestability, for replanting, initiating a gradual process of genetic modification through repeated generations. This unconscious selection—wherein humans inadvertently favored heritable variations by prioritizing plants that produced more usable yields—differentiated domesticated crops from wild types over millennia, as seen in the evolution of wheat (Triticum dicoccum) from wild emmer around 10,000 BCE. In addition to seed selection, vegetative propagation techniques like emerged in ancient civilizations to maintain superior clones and combine traits. Records indicate was practiced by the ancient as early as 2000 BCE and documented in Greek texts around 424 BCE, primarily for trees such as figs and olives to propagate high-quality scions onto disease-resistant rootstocks. Cuttings and layering similarly preserved desirable varieties without reliance on , limiting but ensuring trait stability in crops. These methods relied on observational rather than theoretical , with farmers iteratively refining populations through mass selection of phenotypes like yield, disease resistance, and palatability. By the 17th and 18th centuries, practices became somewhat more deliberate, though still pre-genetic. Rudolf Jakob Camerarius demonstrated plant sexuality in 1694 and advocated crossing for novelty, while figures like Joseph Gottlieb Kölreuter conducted systematic hybridizations in the 1760s, noting hybrid vigor (heterosis) in tobacco and other species without elucidating inheritance patterns. Such efforts marked a transition toward intentional variation but remained constrained by incomplete understanding of pollination control and heritability, with selection continuing to dominate practical crop improvement until Mendel's principles provided a causal framework.

Mendelian Era and Classical Foundations

The rediscovery of Gregor Mendel's laws of inheritance in 1900 marked the onset of the Mendelian era in plant breeding, providing a scientific framework for understanding discrete hereditary traits and enabling systematic selection and hybridization. Mendel had conducted hybridization experiments with pea plants (Pisum sativum) from 1856 to 1863, observing patterns of segregation and independent assortment in seven traits such as seed shape and color, which he published in 1866. These principles, initially overlooked, were independently confirmed in 1900 by , , and , who encountered similar ratios while studying plant hybrids, thus integrating Mendelian ratios into contemporary cytology and breeding practices. Early adopters like championed Mendelism, coining the term "" in 1905 and applying it to predict outcomes in crosses of ornamental plants and crops, which facilitated the identification of dominant and recessive alleles for traits like flower color in sweet peas. This shifted breeding from empirical selection to predictive crossing, allowing breeders to stabilize desired traits through and progeny testing. In , Nils Hermann Nilsson-Ehle extended Mendelian principles to quantitative traits by demonstrating polygenic inheritance in wheat kernel color between 1900 and 1907, showing that red pigmentation resulted from the cumulative effects of three independent genes, with F2 ratios approximating 1:63:6:63:28:63:21:63:1 for colorless to deep red phenotypes. His work at the Svalöf plant breeding station produced improved wheat varieties by selecting recombinant lines from controlled crosses, laying groundwork for handling complex, multifactorial agronomic traits like yield and disease resistance. Classical foundations solidified through the recognition of pure lines by in 1903, who distinguished from via selection experiments in beans, emphasizing that environmental variation masked underlying genetic stability in homozygous populations. Applied to crops, this enabled the isolation of elite lines for multiplication, as seen in early 20th-century corn breeding where exposed recessive traits, paving the way for exploitation. These advancements transformed plant breeding into a deductive , prioritizing verifiable ratios over trial-and-error, though challenges persisted in scaling to polyploids like , where behavior required further cytogenetic integration.

Green Revolution and Hybridization Advances

The , initiated in the mid-20th century, marked a pivotal era in plant breeding characterized by the development of high-yielding crop varieties that substantially boosted agricultural productivity in developing regions. Agronomist , working at the International and Improvement Center (CIMMYT) in from the 1940s, pioneered rust-resistant, semi-dwarf varieties through selective cross-breeding of diverse global with local strains, enabling plants to support heavier grain loads without under high application. These innovations, combined with expanded and chemical inputs, allowed to attain self-sufficiency by 1956, with national yields rising from an average of 750 kilograms per hectare to over threefold in irrigated areas. Borlaug's shuttle breeding technique—alternating plantings between contrasting seasons in Mexico's northern and southern regions—accelerated generation cycles, shortening variety development from years to months and facilitating rapid adaptation to diseases like . By the , these varieties were disseminated to , where adopted them amid threats; production there surged from 12 million tons in 1965 to 20 million tons by 1970, averting mass starvation through yield increases exceeding 50% in responsive agroecosystems. Concurrently, the (IRRI) released in 1966, a semi-dwarf hybrid derivative yielding up to 10 tons per under irrigated, fertilized conditions—far surpassing traditional varieties' 2-3 tons per —and contributing to output doublings in the and by the early 1970s. Hybridization advances underpinned these gains, leveraging (hybrid vigor) and wide crosses to introgress traits such as from Japanese varieties into Mexican and Indian s, enhancing resistance and efficiency. While commercial F1 hybrids, developed in the U.S. from the 1920s and achieving 20-30% yield premiums by the 1930s, predated the Revolution, their principles informed and breeding; breeders combined elite inbred lines to stabilize superior traits in open-pollinated or self-pollinated systems suited to resource-poor farmers. This classical hybridization, distinct from single-cross F1 production, prioritized recessive dwarfing genes and photoperiod insensitivity, enabling double cropping and yield potentials unattainable in taller, traditional landraces. Globally, these breeding efforts tripled production between 1961 and 2000 despite a doubling of and only a 30% expansion in , with and yields rising most sharply—often 2-3 fold in adopting regions—through genotype-by-environment optimization. Borlaug's contributions earned him the 1970 , underscoring breeding's causal role in stabilizing food supplies, though sustained impacts required complementary inputs and infrastructure.

Molecular Era and Post-1980 Developments

The molecular era in plant breeding emerged in the early 1980s, driven by advances in technology that enabled precise gene transfer into plants. Initial breakthroughs involved tumefaciens-mediated transformation, with the first reports of stable transgenic tobacco plants in 1983, demonstrating integration and expression of foreign genes such as those conferring antibiotic resistance. These methods exploited the bacterium's natural to insert T-DNA into the plant genome, initially limited to dicots but later extended through vector modifications. Concurrently, direct gene delivery techniques like and microprojectile (biolistics), developed by mid-decade, overcame barriers in monocots such as and , broadening applicability across species. Molecular markers revolutionized breeding precision during this period. Restriction fragment length polymorphism (RFLP) assays, introduced in the early 1980s, allowed detection of DNA sequence variations linked to traits, facilitating quantitative trait loci (QTL) mapping for complex attributes like yield and stress tolerance. By the late 1980s, these tools supported early-generation selection, reducing breeding cycle times from years to months in some programs. The saw evolution to PCR-based markers like amplified fragment length polymorphisms (AFLPs) and simple sequence repeats (SSRs), which offered higher throughput and codominance, enabling (MAS) in commercial crops such as and for disease resistance. Empirical data from MAS applications showed yield gains of 5-10% in lines by pyramiding favorable alleles without phenotypic in juvenile stages. Genetic engineering transitioned from proof-of-concept to field deployment post-1980. The U.S. Supreme Court's 1980 ruling affirmed patent eligibility for engineered microbes, incentivizing plant applications and leading to herbicide-tolerant tobacco trials by 1986. Insect-resistant traits via (Bt) genes were tested in and by 1987, with regulatory approvals accelerating in the early 1990s. Commercialization began with China's 1992 approval of virus-resistant tobacco, followed by the U.S. launch of Calgene's tomato in 1994, modified with an antisense polygalacturonase gene to extend without quality loss. and glyphosate-tolerant soybeans debuted in 1996, comprising 17% and 54% of U.S. acreage by 2000, respectively, correlating with reduced use by 37% in Bt crops through 1999. By the 2000s, stacked transgenes combined pest resistance and herbicide tolerance, expanding to over 25 countries and 190 million hectares globally by 2020, with , , and dominating adoption for yield stability under biotic stresses. Nutritional enhancements, such as beta-carotene-enriched prototypes in 2000, addressed deficiencies empirically linked to reduced in rice-dependent regions. These developments integrated with classical methods, yielding hybrid vigor in GM lines with 10-20% productivity edges over non-GM counterparts in diverse environments, though regulatory scrutiny and public debates over long-term ecological impacts persisted, with studies attributing minimal risks in contained systems. The era's causal foundation—direct allelic substitution bypassing linkage drag—contrasted prior empirical selection, enabling traits unattainable via hybridization alone, such as novel metabolic pathways.

Classical Breeding Methods

Selection and Hybridization Techniques

Selection techniques in plant breeding focus on identifying and propagating superior individuals from existing populations to enhance desirable traits such as yield, resistance, and . Mass selection, one of the earliest and simplest methods, involves visually selecting plants with favorable phenotypes from a heterogeneous population, harvesting their seeds, and bulking them to form the next generation's planting material; this approach is particularly effective for cross-pollinated crops like where uniformity is not immediately required. Pure-line selection, developed by Wilhelm L. Johannsen in 1903, targets self-pollinated species by isolating homozygous lines through repeated selfing and selection, ensuring genetic uniformity and stability in progeny; it has been widely applied in crops like to purify varieties from landraces. Pedigree selection tracks the ancestry of individual plants from a hybrid cross, selecting progeny based on performance across generations while maintaining detailed records; this method suits both self- and cross-pollinated crops, enabling the fixation of multiple traits over 6-8 generations. Hybridization techniques combine genetic material from distinct parents to generate variability and exploit , or hybrid vigor, for improved performance. Intraspecific hybridization crosses within the same , categorized as intra-varietal (within variety for minor improvements) or inter-varietal (between varieties for broader trait introgression); of the female parent, followed by controlled and bagging to prevent contamination, is standard for preventing in many . integrates a specific trait from a donor parent into an recurrent parent by repeatedly crossing the hybrid progeny back to the recurrent line, typically 5-7 times, to recover over 99% of the recurrent parent's while retaining the target ; this is crucial for traits like disease resistance in crops such as . formation via hybridization includes single, three-way, or double crosses to create diverse breeding , with subsequent selection refining lines for release; in hybrid breeding for crops like , parental inbred lines are maintained separately to produce uniform F1 seeds annually. These methods, reliant on phenotypic evaluation, have underpinned yield gains in major cereals, though they demand large and multiple field trials to account for environmental interactions.

Induced Mutation and Polyploidy

Induced involves the deliberate application of physical or chemical mutagens to plant tissues to generate novel , accelerating the development of desirable traits beyond natural spontaneous rates. Physical mutagens, such as X-rays, gamma rays, or neutrons, were first demonstrated to induce heritable in plants by Lewis Stadler in in 1928, building on Hermann Muller's earlier work with in 1927. Chemical mutagens, including alkylating agents like (EMS), emerged later and allow targeted point , often applied via soaking or treatment. This method has produced over 3,365 officially registered mutant varieties across more than 220 plant species as of 2021, primarily in cereals like , , and , contributing to traits such as improved yield, disease resistance, and shortened maturation time. The Joint FAO/IAEA Division maintains a database tracking these varieties, with notable examples including the 'Calrose 76' developed in the United States in 1975 for semi-dwarf stature and the variety 'Diamant' released in Czechoslovakia in 1966 for high yield under European conditions. Despite its efficacy in generating recessive alleles, induced requires extensive screening of large M1 and M2 populations due to the random nature of , with success rates typically below 0.1% for specific traits. Polyploidy induction complements by artificially doubling sets to create polyploid plants, often enhancing vigor, organ size, and stress tolerance through effects and hybrid-like heterozygosity. Naturally occurring polyploids are common in crops like and potatoes, but induced polyploids are generated using antimitotic agents such as , derived from the autumn (), which binds to disrupt spindle fiber formation during , leading to non-disjunction and . Treatment protocols vary by but commonly involve immersing seeds, meristems, or seedlings in 0.01–0.5% solutions for 6–24 hours, followed by recovery in nutrient media; for instance, 0.01% for 24 hours yielded 27.3% tetraploid plantlets in . Applications include seedless triploid watermelons derived from -induced diploids crossed with tetraploids in , tetraploid for fiber strength, and enlarged-fruit varieties in grapes and bananas, where reduces fertility to favor . While polyploids exhibit gigas effects—larger cells and organs—they can suffer meiotic instability in odd levels (e.g., triploids) and require to stabilize fertility, limiting use in some autogamous crops. Over 100 polyploid cultivars have been commercialized in since , underscoring 's role despite risks mitigated by modern techniques.

Modern Molecular Breeding Techniques

Marker-Assisted and Genomic Selection

(MAS) integrates molecular markers linked to quantitative trait loci (QTLs) or genes of interest to enable indirect selection of desirable genotypes, bypassing the need for phenotypic evaluation in every breeding cycle. This method leverages polymorphisms, such as restriction fragment length polymorphisms (RFLPs) or simple sequence repeats (SSRs), to track of target traits, thereby accelerating breeding for monogenic or oligogenic characteristics like disease resistance. Early applications emerged in the 1980s, with markers used for introgressing exotic into lines, marking a shift from purely phenotypic approaches. By the , MAS facilitated QTL pyramiding in crops such as for bacterial blight resistance, where markers flanking major resistance genes improved selection accuracy over conventional methods. MAS variants include foreground selection for target QTLs, recombinant selection to recover elite backgrounds, and marker-assisted recurrent selection (MARS) for accumulating alleles across cycles. These strategies have proven effective for qualitative traits with large-effect loci, reducing linkage drag and shortening breeding timelines by up to 2-3 generations compared to phenotypic selection alone. However, MAS efficacy diminishes for polygenic traits influenced by numerous small-effect QTLs, as identifying and validating all relevant markers proves resource-intensive and often incomplete due to environmental interactions. Genomic selection (GS) advances beyond MAS by employing genome-wide dense marker arrays—often tens of thousands of single nucleotide polymorphisms (SNPs)—to predict total genetic merit via statistical models like genomic best linear unbiased prediction (GBLUP) or Bayesian approaches. Formally introduced by Meuwissen, Hayes, and Goddard in 2001 for , GS adaptation to accelerated post-2010 with affordable high-throughput sequencing, enabling prediction accuracies exceeding 0.5-0.7 for yield in and training populations. Unlike MAS, GS assumes all markers contribute to trait variation through , obviating the need for prior QTL mapping and capturing epistatic and dominance effects for complex, low-heritability traits. In practice, GS shortens generation intervals by permitting seedling-stage selection based on genomic estimated breeding values (GEBVs), with reported genetic gain increases of 20-50% over phenotypic selection in self-pollinated crops like . Applications span major staples: in , GS integrated with doubled haploids boosted gains; in , it enhanced root yield prediction across diverse environments. Challenges include dependency on large, representative training sets (typically 200-2000 individuals) for model calibration and computational demands for multi-environment genomic prediction, though advancements in hybrids mitigate these. Overall, GS complements MAS in hybrid schemes, where MAS targets major genes and GS refines polygenic backgrounds, yielding synergistic improvements in selection response.

Gene Editing Technologies Including CRISPR

Gene editing technologies facilitate precise alterations to plant genomes by targeting specific DNA sequences, enabling the introduction of beneficial mutations that mimic natural variation or introduce novel traits with minimal unintended changes. Unlike traditional breeding or random , these methods rely on engineered nucleases to create double-strand breaks at predetermined loci, which cells repair through mechanisms such as —resulting in small insertions or deletions—or homology-directed repair for precise substitutions. This precision reduces linkage drag, where undesirable genes are co-inherited with desired ones, accelerating trait improvement in crops. The CRISPR-Cas9 system, adapted from bacterial adaptive immunity, has dominated gene editing since its repurposing as a programmable tool in 2012, with initial plant applications reported in 2013 for transient expression in protoplasts of and . Stable heritable edits followed in 2014, including knockouts conferring powdery mildew resistance in via targeting susceptibility genes TaMLO. Subsequent refinements, such as CRISPR-Cas12a for broader PAM recognition and base/prime editing for single-nucleotide changes without breaks, have expanded capabilities, achieving efficiencies exceeding 90% in some dicot species and enabling multiplex edits of multiple loci simultaneously. These advancements stem from optimizing guide RNAs and delivery via or particle bombardment, minimizing off-target effects—often below 1% with high-fidelity variants—as validated in and trials. In crop breeding, has targeted biotic stresses, such as editing OsSWEET13 in for bacterial blight resistance (2016) and Gb_MLO in for tolerance, yielding lines with 20-50% higher resistance without yield penalties. Abiotic improvements include via ARGOS8 overexpression in , increasing yield by 5-10% under water-limited conditions, and nutritional enhancements like reduced glutenin in for celiac-safe varieties. Yield boosts, such as 10-15% grain increase from TaGW2 edits in , demonstrate multiplex potential, editing up to 100 loci in for polygenic traits. These outcomes outperform conventional methods by generating variants in one generation versus 6-10 years of , though delivery challenges persist in recalcitrant species like cereals.
CropTargeted Gene/TraitOutcomeYearReference
TaMLO / Powdery mildew resistanceKnockout lines with full resistance2014
OsSWEET13 / Bacterial Enhanced resistance, no yield loss2016
ARGOS8 / 5-10% yield increase under stress2017
SlPelo / Fruit size10-20% larger fruits2014
Regulatory frameworks vary; in the United States, site-directed nuclease-1 edits without foreign DNA are exempt from GMO oversight since 2018, treating them akin to conventional breeding products, as they lack transgenes and exhibit mutation spectra similar to chemical . This contrasts with stricter EU rules, where any edit is scrutinized, potentially hindering despite of equivalence—e.g., no risks beyond natural variation. Empirical data from field trials confirm edited crops' stability and equivalence to non-edited counterparts in composition and agronomics, supporting for gains.

Speed Breeding and Doubled Haploidy

Speed breeding is a controlled-environment technique that accelerates generational cycles in by manipulating photoperiod, light intensity, and to promote rapid flowering and seed set, enabling multiple generations per year. First formalized in a 2018 study, it utilizes extended light periods of up to 22 hours daily via energy-efficient LEDs, combined with mild temperatures around 22°C, to shorten life cycles in crops such as spring from 4–6 months to as little as 2 months per generation, achieving up to six generations annually. This approach builds on earlier concepts from NASA's 1980s controlled systems but was adapted for breeding self-pollinated cereals like and , as well as like chickpeas. Doubled haploidy (DH) produces fully homozygous lines in a single generation by inducing haploid plants—possessing half the normal chromosome set—from gametes or embryos, followed by artificial chromosome doubling using agents like colchicine to restore fertility and homozygosity. Common induction methods include wide hybridization (e.g., maize-wheat crosses for wheat haploids) and in vitro androgenesis or gynogenesis from pollen or ovules, with success rates varying by species: over 10% in maize via maternal haploid induction but lower in recalcitrant crops like rice without optimization. Developed since the 1960s for crops like tobacco and barley, DH bypasses multiple self-pollination cycles required in conventional breeding, reducing the time to achieve genetic fixation from 6–8 generations to one, thereby enhancing selection efficiency for traits like disease resistance. When integrated, speed breeding and DH synergize to compress breeding timelines dramatically; for instance, DH lines can be generated and then advanced through 4–6 rapid cycles yearly under speed breeding protocols, facilitating accelerated of traits such as in or yield in canola within 1–2 years versus a decade traditionally. This combination has been applied in programs targeting climate-resilient varieties, with empirical gains including 20–30% faster development of homozygous populations in , though challenges persist in genotype-specific responses and scalability for vegetatively propagated crops. Limitations include elevated costs for controlled chambers and potential selection biases from non-field conditions, necessitating validation in open environments.

AI-Driven Phenotyping and Microbiome Integration

AI-driven phenotyping employs algorithms, , and sensor technologies to automate the measurement and analysis of plant traits at high throughput, surpassing traditional manual methods in speed and precision. For instance, convolutional neural networks process imagery from drones or ground-based sensors to quantify attributes such as leaf area, accumulation, and disease incidence with accuracies exceeding 90% in crops like and . This approach enables breeders to evaluate thousands of genotypes under varied conditions, reducing phenotyping time from weeks to hours and facilitating data-driven selection for complex traits like yield stability. The , comprising root-associated , fungi, and other microbes, influences host nutrient uptake, resistance, and stress tolerance, offering untapped for breeding programs. for microbiome-interactive traits has demonstrated enhanced growth in cultivars that recruit beneficial communities, as seen in studies where lines with optimized microbiomes showed 15-20% improved drought resilience compared to non-selected counterparts. Integrating data into selection pipelines, such as through amplicon sequencing of rhizobiomes, allows prediction of plant performance beyond host alone, with models incorporating microbial variants boosting genomic selection accuracy by up to 10% in field trials. AI bridges phenotyping and microbiome analysis by processing multi-omics datasets to uncover causal links between microbial composition, phenotypic outcomes, and genotypic markers. Deep learning frameworks, for example, integrate rhizosphere metagenomic profiles with high-throughput imaging to identify core microbial taxa correlated with traits like nitrogen use efficiency, enabling predictive modeling of microbiome-mediated phenotypes in breeding populations. In a 2024 maize study, AI-augmented genomic selection incorporating host SNPs and microbial sequence variants improved hybrid prediction accuracy for yield under stress by 8-12%, highlighting the potential for scalable, data-integrated strategies. Such advancements, while promising, require validation across diverse agroecosystems to account for environmental variability in microbiome assembly.

Alternative Breeding Approaches

Participatory and Farmer-Led Breeding

Participatory plant breeding (PPB) involves the systematic collaboration between farmers and professional breeders throughout the crop improvement process, including objective-setting, selection, crossing, evaluation, and , to develop varieties adapted to local agroecological and socioeconomic conditions. This approach originated in the early 1980s as a response to the limitations of centralized conventional breeding in addressing the needs of smallholder farmers in marginal environments, particularly in developing countries where uniform varieties from formal programs often underperformed due to genotype-by-environment interactions. Farmer-led breeding extends PPB by emphasizing greater for farmers in directing selection and experimentation, often using indigenous knowledge and on-farm trials without heavy reliance on external scientists, though it shares PPB's decentralized structure. By 2009, approximately 80 PPB programs existed worldwide, targeting crops such as , , , and potatoes in regions including , , , and . Methods in PPB and farmer-led breeding prioritize on-farm , where farmers conduct mass selection (e.g., selecting 2-5% of plants per cycle), pedigree selection from F2 populations, or recurrent selection for traits like disease resistance and yield stability under low-input conditions. Tools such as mother-baby trials—combining researcher-managed "mother" plots with farmer-managed "baby" plots—and participatory varietal selection (PVS) enable rapid feedback on farmer preferences, often reducing breeding cycles by 3-4 years compared to conventional methods that rely on centralized, multi-location testing. Farmer-led variants incorporate community seed fairs and negative screening (removing susceptible plants) to leverage local genetic resources, enhancing resilience to biotic stresses like or pests without advanced inputs. Empirical evidence from case studies demonstrates PPB's effectiveness in heterogeneous environments. In , farmer-participatory selection of from F3 bulks over four cycles yielded 12 adopted varieties with a 26% yield advantage over conventional releases and coverage of 69% more planted area, alongside 93 total adoptions versus only 2 of 8 conventional varieties. For in , cold-tolerant PPB varieties spread farmer-to-farmer within 10 km and occupied over 30% of the rice area by the late . In , farmer-led composites achieved 4.5% yield gains per selection cycle over five cycles, while NERICA hybrids in had a 14% varietal success rate versus less than 1% in conventional breeding. A pea study in under organic conditions showed farmer-selected lines yielding 23% more than conventional cultivars based on acceptability and yield indices. Compared to conventional breeding, PPB often yields higher benefit-cost ratios (e.g., 39 versus 15 in Syrian , with 46% ) and lower costs (5-28% less), due to targeted adaptation and reduced GEI through on-farm selection, though it may lag in high-input systems where centralized expertise drives broader genetic gains. rates are elevated because varieties align with farmer criteria like taste, storability, and market fit, fostering empowerment and preservation; however, scalability challenges arise from resource limitations and variable farmer expertise, necessitating hybrid models with scientific support for .

Evolutionary and Dynamic Breeding

Evolutionary plant breeding entails the development of genetically diverse crop populations, such as composite cross populations (CCPs), which are subjected to recurrent cycles of natural and artificial selection across multiple generations to foster adaptation to local environmental pressures. This approach begins with the hybridization of numerous parental lines to generate initial diversity, followed by equalization of seed proportions and repeated sowing of harvested bulk seed without rigorous individual selection, allowing evolutionary forces like recombination, mutation, and selection to shape the population over time. Pioneered by C.A. Suneson in 1956 for barley, the method leverages self-pollinating cereals' capacity for limited outcrossing to maintain heterogeneity, contrasting with conventional breeding's emphasis on uniform inbred lines. Empirical studies demonstrate that such populations evolve measurable resistance to pathogens; for instance, in barley CCPs, frequency of alleles conferring resistance to powdery mildew increased significantly after 10-15 generations under disease pressure in field trials. The dynamic aspect of this breeding arises from its ongoing, decentralized nature, where populations continue to evolve post-release through farmer-managed reseeding, enabling continuous adaptation to fluctuating conditions like variability and pest dynamics without reliance on external inputs. In , evolutionary populations derived from multi-parent crosses exhibited 10-20% greater yield stability across diverse European sites compared to standard varieties, attributed to retained genetic variance that buffers against abiotic stresses. Hungarian trials with CCPs using 7-12 parents optimized diversity-retention balance, yielding populations with enhanced competitive ability in low-input systems after 5-8 cycles. This method's efficacy stems from causal mechanisms like via occasional cross-pollination (1-5% in cereals) and selection gradients imposed by site-specific biotic and abiotic factors, as evidenced by longitudinal data from Allard's experiments spanning 1960-1980, where populations differentiated rapidly by locale. Applications extend to organic agriculture, where evolutionary populations reduce dependency on synthetic pesticides; for example, CCPs in U.S. trials showed 15-25% lower disease incidence and maintained yields under organic management over four generations. Long-term programs, such as those evolving over 24 years in , have produced lines with superior performance under recurrent selection, underscoring the approach's potential for sustainable intensification amid environmental uncertainty. While effective for self-pollinators like and , scalability challenges include slower initial gains relative to marker-assisted methods and the need for diverse starting to avoid . Peer-reviewed field data affirm its role in preserving agrobiodiversity, with populations retaining 70-90% heterozygosity longer than cultivars.

Primary Goals and Outcomes

Enhancing Yield and Productivity

Plant breeding enhances and productivity primarily through genetic selection for traits that optimize resource capture, conversion efficiency, and partitioning to harvestable organs. Key mechanisms include increasing photosynthetic capacity, improving harvest index—the ratio of grain to total biomass—and reducing losses from or inefficient stature. For example, the introduction of semi-dwarf varieties in cereals allowed denser planting and higher application without yield penalties from , directly boosting productivity. Historical data demonstrate substantial genetic gains from breeding efforts. In the United States, yields per acre increased from about 13 bushels in 1888 to 45 bushels by 2018, with the majority of post-1940 gains linked to varietal improvements. Globally, yields rose by 225%, by 196%, by 146%, and soybeans by 153% over recent decades, with variety advancements—products of breeding—accounting for a significant portion of these increases. In spring wheat breeding programs, annual yield gains averaged 0.61% from 1960 to 2023, without compromising protein content. Crop-specific examples highlight breeding's impact. harvest index has shown a relative genetic increase of 0.26% per year since 1964, reflecting selections for better allocation to . In under irrigated conditions, genetic yield gains since 1905 averaged 0.544% annually, accelerating to 0.822% in more recent elite varieties. However, total yield improvements often combine genetic progress with agronomic practices; analyses of trials attribute 13% to 50% of gains directly to genetic enhancements, underscoring breeding's foundational role amid complementary factors like climate trends and management. Ongoing breeding continues to target yield potential by integrating traits like enhanced stress tolerance and nutrient efficiency, though genetic gains must outpace environmental challenges to sustain . Peer-reviewed estimates indicate that while conventional phenotypic selection yielded modest annual progress, modern approaches like genomic selection promise to accelerate rates by 50-100% through precise trait prediction. These outcomes affirm breeding's causal contribution to , with from long-term trials validating the and stability of selected yield traits across environments.

Improving Resistance to Biotic and Abiotic Stresses

Breeding programs target biotic stresses, including pathogens like fungi, , and viruses, as well as insect pests, which cause an estimated 20-40% of annual global crop production losses. Conventional methods involve crossing cultivars with relatives or landraces harboring resistance genes, followed by phenotypic selection over multiple generations. (MAS) accelerates this by using DNA markers linked to quantitative trait loci (QTL) for traits like disease resistance; for instance, MAS has enabled pyramiding of genes conferring resistance to stem ( graminis) and stripe rust ( striiformis) in , with KASP markers facilitating precise integration of resistance alongside agronomic traits in breeding lines released as of 2025. In lettuce, MAS targeting markers for resistance to downy mildew ( lactucae) has improved selection accuracy and speed compared to traditional screening, reducing breeding cycles from years to months. Genetic engineering and genome editing further enhance biotic resistance by targeting susceptibility (S) genes or overexpressing defense-related transcription factors. CRISPR/Cas9 editing has successfully knocked out S-genes in crops like and , conferring broad-spectrum resistance to bacterial blight and other pathogens without introducing foreign DNA, as demonstrated in field trials showing reduced lesion sizes and infection rates. Transgenic approaches, such as toxin expression in cotton and maize, have provided durable insect resistance; adoption in since 2002 increased yields by 24% and reduced use by 37% in smallholder farms, though efficacy can wane with pest adaptation, necessitating stacked traits. Abiotic stresses, including , , , and flooding, impose yield penalties of 50-70% in major crops under severe conditions. Breeding for abiotic tolerance often leverages QTL mapping and MAS to introgress traits from tolerant progenitors; in , the Saltol QTL, identified in 2006, has been deployed via MAS in varieties like IRRI-developed lines, enabling growth in saline soils with 1-2 dS/m electrical conductivity and yield stability up to 20% higher than sensitive checks in coastal fields. For , genomic selection models incorporating multi-environment trial data have accelerated gains in , with hybrids exhibiting 5-15% yield advantages under water stress in trials conducted through 2020. Advanced tools like have edited genes such as DREB1A in and , enhancing efficiency and root architecture for , with edited lines showing 25-30% less loss in controlled experiments. In , multiplex targeting of heat-stress susceptibility factors improved fruit set under 35°C conditions by 40%, addressing reproductive-stage vulnerabilities. Combined stress tolerance—simulating field realities of plus pathogens—remains challenging due to antagonistic gene interactions, but transcription factors like NAC family members, when overexpressed via transgenics, have boosted resilience in cereals by coordinating multiple pathways, as evidenced in lines withstanding combined and infection. These outcomes underscore breeding's role in stabilizing production amid climate variability, though polygenic traits demand large populations and multi-site validation to ensure durability.

Nutritional and Quality Improvements

Plant breeders have targeted nutritional enhancements primarily through , which involves selecting and crossing varieties to increase density in edible crop parts, addressing deficiencies like , iron, and that affect billions globally. This approach leverages in wild relatives or landraces to elevate provitamin A , iron, or without relying on genetic modification in many programs. By 2023, biofortified staples reached over 330 million consumers across more than 40 countries, with adoption driven by comparable or superior yields and agronomic performance. Prominent examples include , engineered but bred for integration into local varieties, providing up to 35 μg per gram, which humans convert efficiently to at rates supporting dietary needs. Orange-fleshed , biofortified for via conventional breeding, has been the most successful such initiative in , improving status in populations with high deficiency rates. Iron- and zinc-enriched , , developed by programs like HarvestPlus, have demonstrated bioavailability improvements, reducing prevalence in trials among deficient groups. These varieties maintain yield potential, with higher nutrient lines often showing resilience to stresses, facilitating farmer uptake. Quality improvements via breeding focus on traits enhancing post-harvest utility, sensory appeal, and safety, such as reduced allergenicity and extended . Breeders have used and selection to lower peanut allergens like Ara h 2, potentially decreasing reaction severity without yield loss. In , targeted breeding has produced low-gluten lines via techniques like TILLING, aiding celiac management while preserving baking quality. For , selection for firmer textures and delayed ripening in fruits like strawberries has extended marketability, reducing spoilage losses through conventional crosses. These modifications improve processing efficiency, such as oil stability in soybeans, and consumer acceptance through better flavor profiles, though allergen reductions require rigorous testing for efficacy. Overall, such breeding yields multifunctional crops balancing , durability, and palatability.

Intellectual Property Frameworks

Plant Variety Protection Systems

Plant variety protection systems, also known as plant breeders' rights, provide intellectual property protection specifically tailored to new, sexually reproduced or tuber-propagated plant varieties, distinct from utility patents by accommodating the biological realities of plant reproduction such as seed saving and further breeding. These systems grant breeders exclusive rights to produce, sell, or market the protected variety and its harvested material for a limited term, typically 20 to 30 years depending on the crop and jurisdiction, thereby incentivizing investment in breeding innovation while balancing access for farmers and researchers. Protection requires varieties to meet criteria of novelty (not commercially exploited prior to application), distinctness (differing from known varieties), uniformity (sufficiently consistent), and stability (maintaining traits over generations), verified through standardized testing protocols. The international framework for these systems is the International Union for the Protection of New Varieties of Plants (UPOV), established by the 1961 Convention in , with subsequent revisions in 1972, 1978, and 1991 to strengthen breeders' rights and harmonize national laws. As of 2023, UPOV has 78 member states, promoting PVP to foster agricultural innovation, increase variety diversity, and enhance global by enabling breeders to recoup development costs, which can exceed millions per variety. Under UPOV, protected rights allow breeders to authorize or prohibit commercial exploitation but include exceptions for non-commercial use, experimental purposes, and breeding essentially derived varieties or those not distinctly different, though the 1991 revision limits farm-saved seed practices more stringently than earlier versions to protect commercial interests. In the United States, the Plant Variety Protection Act (PVPA) of December 24, 1970, administered by the of the USDA, extends protection to asexually reproduced varieties via patents but focuses PVP on sexually reproduced ones, offering certificates valid for 20 years (25 years for trees, vines, and tubers). The PVPA, amended in 1994 to align more closely with UPOV 1991, permits limited exemptions such as saving seed for the farmer's own use on their holdings and breeding, but enforces against unauthorized sales or exports, with over 10,000 certificates issued by 2023 supporting U.S. crop improvements in , soybeans, and . The operates the Community Plant Variety Rights (CPVR) system, effective since April 27, 1998, under Council Regulation (EC) No 2100/94 and managed by the Community Plant Variety Office (CPVO) in , , providing uniform, EU-wide protection without national filings. CPVRs grant 25 years of exclusivity (30 for trees, vines, potatoes), covering production, conditioning, and marketing, with technical examinations ensuring DUS compliance across 28 member states plus associated territories; by 2023, the CPVO had registered over 70,000 varieties, facilitating cross-border breeding in ornamentals, field crops, and fruits while allowing exceptions for private breeding and farm-saved seed under compulsory licensing in some cases.
JurisdictionAdministering BodyTerm of ProtectionKey ExemptionsAlignment with UPOV
(PVPA)USDA AMS20 years (25 for trees/vines)Farm-saved seed for own use; research1994 amendments to 1991 Convention
European Union (CPVR)CPVO25 years (30 for specific crops)Private/non-commercial use; breeding derivativesFull compliance with 1991 Convention
These systems emerged from mid-20th-century efforts to address the inadequacy of general laws for , with early national laws in (1933) and the (1941) preceding UPOV, and have demonstrably boosted variety registrations—UPOV studies show member countries registering 2-3 times more new varieties annually than non-members—though debates persist on their impact on smallholder farmers in developing regions where stricter enforcement may limit traditional practices.

Patenting in Genetic Modification

Utility patents under provide the primary mechanism for protecting genetically modified , encompassing the engineered genetic sequences, transformation methods, and the resulting plant varieties as compositions of matter or processes. These differ from plant variety protection (PVP) under the Plant Variety Protection Act, which excludes sexually reproduced hybrids and varieties produced by , offering utility patents broader scope including claims to specific genes, traits, and reproductive materials. In practice, major GM crops like herbicide-tolerant soybeans and insect-resistant corn have been patented this way, enabling companies to control reproduction and distribution. The legal foundation emerged from the U.S. 's 1980 decision in , which held that man-made microorganisms, including those genetically engineered, constitute patentable subject matter under 35 U.S.C. § 101 as they are not naturally occurring products of nature. This principle extended to via the U.S. Patent and Trademark Office's 1985 Ex parte Hibberd ruling, granting the first utility patent for a genetically engineered (a cell line). The affirmed utility patents' applicability to plant varieties in J.E.M. Ag Supply, Inc. v. Pioneer Hi-Bred International, Inc. (2001), ruling that such protections supplement but do not preclude PVP, even for seed-reproduced . To qualify, GM plant inventions must demonstrate utility (practical application, such as pest resistance), novelty (not anticipated by ), non-obviousness (not an incremental change evident to a skilled breeder), and enablement (sufficient disclosure for replication, often requiring seed deposits in public repositories like the American Type Culture Collection). Patents typically last 20 years from filing, covering progeny seeds and barring unauthorized saving or replanting, as upheld in Monsanto Co. v. Bowman (2013), where the enforced exhaustion limits only to the purchased seed generation. In the , Directive 98/44/EC harmonizes biotech patenting, permitting claims on GM plants if they involve a technical solution to a problem via genetic intervention, excluding naturally occurring sequences but allowing isolated or modified ones with inventive steps. The requires similar criteria, with deposits for microorganisms under the , though exclusions apply to plant varieties per se if not qualifying as microbiological processes. Globally, the mandates patents for microorganisms but leaves plants to national discretion, leading many countries to adopt utility-style protections for GM innovations to incentivize investment amid high R&D costs exceeding $100 million per trait.

Balancing Innovation Incentives with Access

Intellectual property frameworks in plant breeding, such as plant variety protection (PVP) under the UPOV Convention and utility patents, aim to incentivize private investment in by granting exclusive to breeders for a limited period, typically 20-25 years, enabling recovery of costs estimated at tens of millions per variety. Empirical analyses indicate that stronger PVP systems correlate with increased varietal improvements and , as seen in UPOV member states where private-sector breeding output rose following adoption, with studies documenting a positive relationship between breeders' and yield gains in crops like and . For instance, the expansion of protections in the U.S. after 1980 contributed to accelerated commercialization of and heightened private R&D spending, which grew from about 20% of total agricultural R&D in the to over 50% by the 2010s. However, these protections can restrict farmers' access to seeds, particularly through prohibitions on saving, replanting, or exchanging harvested , which traditionally accounts for 70-90% of use among smallholder farmers in developing regions. Under strict regimes, such as those applied to many U.S. hybrid and GM varieties, farmers must purchase new annually, increasing costs—often 10-20% of production expenses—and fostering dependency on commercial suppliers, which has been linked to financial strain for independent operations. PVP systems, as outlined in the UPOV 1991 Act ratified by over 70 countries since , mitigate this somewhat via a "farmer's privilege" allowing limited for non-commercial replanting and a "breeder's exemption" permitting use of protected varieties in further breeding without permission, thereby balancing incentives with ongoing innovation cycles. Yet, the 1991 revisions narrowed these exceptions compared to the 1978 Act, prompting debates over reduced access in low-income contexts where informal systems support and resilience. Efforts to reconcile these tensions include protections under the WTO's (1994), which permits flexible national systems accommodating farmers' practices, as implemented in countries like via the Protection of Plant Varieties and Farmers' Rights Act (2001), granting breeders rights alongside explicit farmers' entitlements to save, exchange, and sell farm-saved . Public breeding programs and open-access repositories, such as those from the centers, provide royalty-free varieties to counterbalance private IP dominance, with evidence showing they enhance adoption in resource-poor areas without eroding overall incentives. Nonetheless, critics, including analyses from agricultural economists, argue that concentrated market power from IP consolidation—evident in mergers reducing firms from 13 to 4 major players by 2015—may inflate prices and limit variety diversity, though productivity data from IP-adopting regions suggest net gains in output per hectare. Ongoing reforms, such as compulsory licensing provisions in some jurisdictions, seek to calibrate exclusivity against public needs, informed by UPOV's own impact assessments showing sustained breeding investment amid access safeguards.

Key Controversies and Debates

GMO Safety, Efficacy, and Regulatory Overreach

Genetically modified organisms (GMOs) in plant breeding involve the precise insertion of genes to confer traits such as pest resistance or nutritional enhancement, and extensive peer-reviewed studies have found no substantiated evidence of unique health risks compared to conventionally bred crops. The National Academy of Sciences concluded in its 2016 report that foods derived from genetically engineered crops pose no greater risk to human health than those from conventional breeding methods, based on analyses of agronomic, health, and environmental data spanning decades. A systematic review of animal and human studies on GM food consumption similarly reported no adverse effects/events attributable to the genetic modifications themselves. After 28 years of commercial deployment since 1996, no verified cases of harm to human consumers from approved GM crops have emerged, with modifications often improving efficiency and reducing pest losses. In terms of efficacy, GM crops have demonstrably boosted , with a of 147 studies across multiple crops showing average yield increases of 22%, pesticide reductions of 37%, and farmer profit gains of 68% from adoption. For instance, genetically engineered exhibited grain yields 5.6% to 24.5% higher than non-engineered comparators in field trials, alongside lower concentrations. Globally, GM crop cultivation from 1996 to 2013 contributed over 370 million additional tonnes in food crop yields, aiding in both developed and developing regions without evidence of yield plateaus. These outcomes stem from targeted traits like insect resistance and herbicide tolerance, which enable more precise farming practices than random mutations in traditional breeding. Regulatory frameworks for GMOs, however, often impose disproportionate scrutiny relative to their risk profile, treating precise genetic insertions as inherently riskier than chemical or wide-cross hybridization used in conventional breeding, despite lacking empirical justification for such distinction. This has led to criticisms of overreach, exemplified by —a GM variety engineered to produce beta-carotene for prevention—which faced over a decade of approval delays in key markets like the and due to stringent biosafety reviews, despite its non-novel proteins and equivalence to approved GM crops. Such delays have been estimated to forego benefits equivalent to millions of preventable deaths from -related blindness and mortality, with one analysis attributing 1.4 to 2.1 million child deaths annually to the absence of this technology during regulatory holdups. Scientists argue that harmonizing GMO oversight with process-based risks of traditional methods, rather than product-based evidence, would accelerate beneficial innovations without compromising safety, as no differential hazards have been identified.

Biodiversity Impacts and Monoculture Risks

The replacement of diverse landraces and traditional varieties with high-yielding modern cultivars developed through has led to , defined as the accelerated loss of within crop gene pools due to the dominance of genetically narrower elite breeding lines. This process diminishes the availability of adaptive for traits like disease resistance or , as farmers prioritize uniform hybrids optimized for mechanized and market demands over heterogeneous local varieties. Empirical studies document declines in on-farm , with peer-reviewed analyses confirming reduced heterozygosity and allele richness in major staples such as , , and since the . A frequently cited figure posits that approximately 75% of global genetic diversity in was lost between 1900 and 2000, attributed to the widespread adoption of fewer, high-performing varieties. However, this estimate originates from early FAO extrapolations with limited baseline data on pre-industrial diversity, and subsequent critiques highlight that while initial shifts caused erosion, recent trends in variety releases and gene bank collections have partially offset losses in formal sector diversity, though on-farm and wild relative diversity continues to decline. Such erosion impacts broader by reducing between crops and wild relatives, potentially accelerating risks for underutilized and limiting ecosystem services like and . Monoculture systems, enabled by breeding for genetic uniformity to facilitate uniform ripening and harvest, amplify vulnerabilities to biotic threats, as synchronized crop growth allows pests or pathogens to exploit shared weaknesses across vast areas. Historical cases illustrate these risks: the Irish Potato Famine (1845–1852) resulted from near-total dependence on the genetically uniform "Lumper" variety, which lacked resistance to Phytophthora infestans, causing crop failure and over one million deaths. Similarly, the 1970–1971 southern corn leaf blight epidemic in the United States destroyed about 15% of the corn crop—equivalent to roughly $1 billion in losses at the time—because 70–85% of hybrids incorporated the same Texas cytoplasmic male sterility for hybrid seed production, rendering them susceptible to the fungal pathogen Bipolaris maydis. These vulnerabilities extend to abiotic stresses and emerging threats, where monocultures deplete soil nutrients faster due to identical demands, fostering erosion and reduced resilience to climate variability. In regions with intensive monoculture, pesticide resistance develops more rapidly, as uniform host populations enable pathogen evolution without natural genetic barriers. While ex situ conservation in gene banks mitigates some losses—holding over 4 million accessions globally—insufficient integration into breeding programs limits restoration of field-level diversity, underscoring ongoing risks to long-term agricultural stability.

Breeders' Rights vs. Traditional Seed Practices

Plant , established through frameworks like the International Union for the Protection of New Varieties of Plants (UPOV) Convention, grant exclusive control over the production, reproduction, and distribution of novel plant varieties for a limited period, typically 20 to 25 years, to incentivize investment in breeding research and development. These rights emerged prominently in the , with the UPOV Convention first adopted in 1961 and revised in 1972 and 1991, aiming to balance innovation with agricultural needs by protecting asexually and sexually reproduced varieties distinct from existing ones. In the United States, the Plant Variety Protection Act (PVPA) of 1970 provides similar protections for sexually reproduced varieties, excluding those reproduced asexually or via tubers, while allowing limited exemptions. Traditional seed practices, prevalent for millennia, involve farmers selecting, , and replanting seeds from their harvests, often exchanging or selling them locally without formal restrictions, fostering local adaptation and through open-pollinated varieties. This commons-based approach historically enabled self-sufficiency, particularly among small-scale and subsistence farmers, by treating seeds as a derived from natural reproduction rather than proprietary innovation. However, the introduction of protected varieties disrupts this cycle, as farmers using such seeds must generally purchase fresh stock annually or face infringement claims, since and replanting often violates exclusive rights unless exempted. Central to mitigating conflicts are the breeders' exemption and farmers' privilege. The ' exemption permits the use of protected varieties as parental material to develop new, distinct varieties without infringing the original rights, promoting iterative by allowing subsequent to build on prior work without permission or royalty. Under the UPOV 1991 Act, this exemption is mandatory and unconditional for breeding purposes, though optional for other experimental acts done privately or non-commercially. The farmers' privilege, variably implemented, allows limited saving of harvested seed for replanting on the same but prohibits exchange, sale, or use beyond personal needs, with national laws determining its scope—narrower in UPOV 1991 adherents compared to the more permissive 1978 version. In the U.S. PVPA, farmers may save seed for their own use under , but patented varieties, including many genetically modified ones, impose stricter contracts forbidding reuse. Proponents argue that breeders' rights drive productivity gains by recouping R&D costs, with U.S. agricultural productivity rising post-PVPA due to expanded private-sector variety development, evidenced by increased yields in crops like corn and soybeans from protected hybrids. From 1990 to 2020, stronger IP protections correlated with heightened seed innovation, though accompanied by market consolidation and price increases averaging 170% for patented crop seeds. Critics, including smallholder advocates, contend that these rights erode traditional autonomy, forcing annual seed purchases that burden low-income farmers—particularly in developing nations adopting UPOV 1991—while limiting access to diverse, non-proprietary germplasm and potentially reducing on-farm biodiversity through reliance on uniform commercial varieties. Empirical studies show mixed economic outcomes: while protected seeds can lower per-unit production costs via higher yields, small farmers face net financial strain from premiums and restrictions, exacerbating disparities without proportional benefits in non-industrialized contexts. Debates persist over whether compulsory licensing or expanded exemptions could reconcile incentives with customary practices, as unrestricted reuse historically free-rode on breeding efforts, deterring investment in traits like disease resistance.

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