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Peronospora
Peronospora is a genus of downy mildews that are obligate plant pathogens. They can cause severe damage to many different cultivated crops, as well as wild and ornamental plants. Peronospora is most closely related to Pseudoperonospora, and together they form the clade of downy mildews with coloured conidia. Peronospora has far more species than any other genus of the downy mildews. However, many species have been moved from this genus to other genera based on phylogenetic evidence. Among these are the species now in Hyaloperonospora, important pathogens of the Brassicaceae. Now, the Peronospora species of most importance is likely Peronospora tabacina.[opinion] Peronospora tabacina causes blue mold on tobacco plants and can severely reduce yields of this economically important crop to the point where it has been classified as a bioweapon.
Peronospora was first described in 1837 by August Carl Joseph Corda, a Czech mycologist and physician, in his first of six volumes of his Icones fungorum hucusque cognitorum. Since then, many of the species originally placed in Peronospora have been allocated to other genera or given rise to new genera based on new techniques such as molecular genetics.
There was an epidemic in 1960 of Peronospora tabacina affecting tobacco plants leading to $25 million in losses across eleven countries, which was about 30 percent of the tobacco plants. Another epidemic that was caused by Peronospora destructor reduced the yield of sweet onions by 25 percent in Georgia, USA in 2012, and led to an estimated $18.2 million in losses.
Most of the Peronospora species are highly specific to their hosts and can generally be found anywhere the host plant grows, or is being cultivated. A large portion of their life cycle is spent inside their host plant. Many species of Peronospora are seedborne pathogens, so the worldwide spread of Peronospora crop-plant pathogens is likely to be a result of unknowingly trading infected seeds to new areas. There are also many Peronospora species that are spread by wind currents, which allows them to disperse over large distances. Peronospora species prefer humid air and cool temperatures.
One clade in the genus is known as the floricolous downy mildews. These species produce conidiophores exclusively on the flowers of their hosts.
The first stage in the Peronospora life history is the sporangia. The sporangia are small spore-like structures about 65 um long that germinate a germ-tube when they are near a leaf stoma. A germ tube will come from the sporangium and penetrate the leaf cell where it will form a haustorium. The haustorium absorbs nutrients from the leaf, while hyphae invade the intercellular space, and the leaf will eventually develop a lesion. These lesions often start out yellow and then turn brown as the leaf starts to undergo necrosis. From here, Peronospora can undergo either asexual reproduction or sexual reproduction. Asexual reproduction occurs when the air outside is moist making for favourable conditions. During asexual reproduction, hyphae on the host plant will form sporangiophores, which will produce conidia. The conidia will be dispersed by the wind is able to infect other plants. The asexual cycle only takes five to seven days to complete. Sexual reproduction occurs when the conditions are unfavourable and it needs to withstand harsh environmental conditions. During sexual reproduction, the hyphae will undergo meiosis forming antheridia and oogonia, the only haploid structures in the Peronospora life history. The antheridia will fuse to the oogonia, initiating plasmogamy and then karyogamy, and will result in the production of many oospores. The oospores can then be dispersed by the wind to infect more plants.
Both Peronospora and Pseudoperonospora are characterized by their ability to produce melanized sporangia, but Pseudoperonospora produces zoospores whereas Peronospora cannot.
The model oomycete pathogen, Peronospora parasitica, used to be included in this genus, however it has been reclassified to the genus Hyaloperonospora.
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Peronospora
Peronospora is a genus of downy mildews that are obligate plant pathogens. They can cause severe damage to many different cultivated crops, as well as wild and ornamental plants. Peronospora is most closely related to Pseudoperonospora, and together they form the clade of downy mildews with coloured conidia. Peronospora has far more species than any other genus of the downy mildews. However, many species have been moved from this genus to other genera based on phylogenetic evidence. Among these are the species now in Hyaloperonospora, important pathogens of the Brassicaceae. Now, the Peronospora species of most importance is likely Peronospora tabacina.[opinion] Peronospora tabacina causes blue mold on tobacco plants and can severely reduce yields of this economically important crop to the point where it has been classified as a bioweapon.
Peronospora was first described in 1837 by August Carl Joseph Corda, a Czech mycologist and physician, in his first of six volumes of his Icones fungorum hucusque cognitorum. Since then, many of the species originally placed in Peronospora have been allocated to other genera or given rise to new genera based on new techniques such as molecular genetics.
There was an epidemic in 1960 of Peronospora tabacina affecting tobacco plants leading to $25 million in losses across eleven countries, which was about 30 percent of the tobacco plants. Another epidemic that was caused by Peronospora destructor reduced the yield of sweet onions by 25 percent in Georgia, USA in 2012, and led to an estimated $18.2 million in losses.
Most of the Peronospora species are highly specific to their hosts and can generally be found anywhere the host plant grows, or is being cultivated. A large portion of their life cycle is spent inside their host plant. Many species of Peronospora are seedborne pathogens, so the worldwide spread of Peronospora crop-plant pathogens is likely to be a result of unknowingly trading infected seeds to new areas. There are also many Peronospora species that are spread by wind currents, which allows them to disperse over large distances. Peronospora species prefer humid air and cool temperatures.
One clade in the genus is known as the floricolous downy mildews. These species produce conidiophores exclusively on the flowers of their hosts.
The first stage in the Peronospora life history is the sporangia. The sporangia are small spore-like structures about 65 um long that germinate a germ-tube when they are near a leaf stoma. A germ tube will come from the sporangium and penetrate the leaf cell where it will form a haustorium. The haustorium absorbs nutrients from the leaf, while hyphae invade the intercellular space, and the leaf will eventually develop a lesion. These lesions often start out yellow and then turn brown as the leaf starts to undergo necrosis. From here, Peronospora can undergo either asexual reproduction or sexual reproduction. Asexual reproduction occurs when the air outside is moist making for favourable conditions. During asexual reproduction, hyphae on the host plant will form sporangiophores, which will produce conidia. The conidia will be dispersed by the wind is able to infect other plants. The asexual cycle only takes five to seven days to complete. Sexual reproduction occurs when the conditions are unfavourable and it needs to withstand harsh environmental conditions. During sexual reproduction, the hyphae will undergo meiosis forming antheridia and oogonia, the only haploid structures in the Peronospora life history. The antheridia will fuse to the oogonia, initiating plasmogamy and then karyogamy, and will result in the production of many oospores. The oospores can then be dispersed by the wind to infect more plants.
Both Peronospora and Pseudoperonospora are characterized by their ability to produce melanized sporangia, but Pseudoperonospora produces zoospores whereas Peronospora cannot.
The model oomycete pathogen, Peronospora parasitica, used to be included in this genus, however it has been reclassified to the genus Hyaloperonospora.