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Magnaporthe grisea
Magnaporthe grisea, also known as rice blast fungus, rice rotten neck, rice seedling blight, blast of rice, oval leaf spot of graminea, pitting disease, ryegrass blast, Johnson spot, neck blast, wheat blast and Imochi (稲熱), is a plant-pathogenic fungus and model organism that causes a serious disease affecting rice. It is now known that M. grisea consists of a cryptic species complex containing at least two biological species that have clear genetic differences and do not interbreed. Complex members isolated from Digitaria have been more narrowly defined as M. grisea. The remaining members of the complex isolated from rice and a variety of other hosts have been renamed Magnaporthe oryzae, within the same M. grisea complex. Confusion on which of these two names to use for the rice blast pathogen remains, as both are now used by different authors.
Members of the M. grisea complex can also infect other agriculturally important cereals including wheat, rye, barley, and pearl millet causing diseases called blast disease or blight disease. Rice blast causes economically significant crop losses annually. Each year it is estimated to destroy enough rice to feed more than 60 million people. The fungus is known to occur in 85 countries worldwide and as of 2003[update] was the most devastating fungal plant pathogen in the world.
M. grisea is an ascomycete fungus. It is an extremely effective plant pathogen as it can reproduce both sexually and asexually to produce specialized infectious structures, appressoria, that infect aerial tissues and hyphae that can infect root tissues.
Rice blast has been observed on rice strains M-201, M-202, M-204, M-205, M-103, M-104, S-102, L-204, Calmochi-101, with M-201 being the most vulnerable. Initial symptoms are white to gray-green lesions or spots with darker borders produced on all parts of the shoot, while older lesions are elliptical or spindle-shaped and whitish to gray with necrotic borders. Lesions may enlarge and coalesce to kill the entire leaf. Symptoms are observed on all above-ground parts of the plant. Lesions can be seen on the leaf collar, culm, culm nodes, and panicle neck node. Internodal infection of the culm occurs in a banded pattern. Nodal infection causes the culm to break at the infected node (rotten neck). It also affects reproduction by causing the host to produce fewer seeds. This is caused by the disease preventing maturation of the actual grain.
The pathogen infects as a spore that produces lesions or spots on parts of the rice plant such as the leaf, leaf collar, panicle, culm and culm nodes. Using a structure called an appressorium, the pathogen penetrates the plant. The appressorium cell wall is chitinous and its inner side contains melanin. which is necessary to damage host structures. The turgor pressure generated during this process is sufficient to penetrate the plants' cuticles routinely, and experimentally can penetrate Kevlar. This impressive turgor is produced by synthesis of glycerol and maintained by the aforementioned appressorial melanin. The pathogen is able to move between the plant cells using its invasive hyphae to enter through plasmodesmata. M. grisea then sporulates from the diseased rice tissue to be dispersed as conidiospores. After overwintering in sources such as rice straw and stubble, the cycle repeats.
A single cycle can be completed in about a week under favorable conditions where one lesion can generate up to thousands of spores in a single night. Disease lesions, however, can appear in three to four days after infection. With the ability to continue to produce the spores for over 20 days, rice blast lesions can be devastating to susceptible rice crops.
Infection of rice induces phosphorylation of the light-harvesting complex II protein LHCB5 . LHCB5 is required for a reactive oxygen species burst produced by the host which provides resistance against this pathogen.
Rice blast is a significant problem in temperate regions and can be found in areas such as irrigated lowland and upland. Conditions conducive for rice blast include long periods of free moisture and/or high humidity, because leaf wetness is required for infection. Sporulation increases with high relative humidity and at 25–28 °C (77–82 °F), spore germination, lesion formation, and sporulation are at optimum levels.
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Magnaporthe grisea
Magnaporthe grisea, also known as rice blast fungus, rice rotten neck, rice seedling blight, blast of rice, oval leaf spot of graminea, pitting disease, ryegrass blast, Johnson spot, neck blast, wheat blast and Imochi (稲熱), is a plant-pathogenic fungus and model organism that causes a serious disease affecting rice. It is now known that M. grisea consists of a cryptic species complex containing at least two biological species that have clear genetic differences and do not interbreed. Complex members isolated from Digitaria have been more narrowly defined as M. grisea. The remaining members of the complex isolated from rice and a variety of other hosts have been renamed Magnaporthe oryzae, within the same M. grisea complex. Confusion on which of these two names to use for the rice blast pathogen remains, as both are now used by different authors.
Members of the M. grisea complex can also infect other agriculturally important cereals including wheat, rye, barley, and pearl millet causing diseases called blast disease or blight disease. Rice blast causes economically significant crop losses annually. Each year it is estimated to destroy enough rice to feed more than 60 million people. The fungus is known to occur in 85 countries worldwide and as of 2003[update] was the most devastating fungal plant pathogen in the world.
M. grisea is an ascomycete fungus. It is an extremely effective plant pathogen as it can reproduce both sexually and asexually to produce specialized infectious structures, appressoria, that infect aerial tissues and hyphae that can infect root tissues.
Rice blast has been observed on rice strains M-201, M-202, M-204, M-205, M-103, M-104, S-102, L-204, Calmochi-101, with M-201 being the most vulnerable. Initial symptoms are white to gray-green lesions or spots with darker borders produced on all parts of the shoot, while older lesions are elliptical or spindle-shaped and whitish to gray with necrotic borders. Lesions may enlarge and coalesce to kill the entire leaf. Symptoms are observed on all above-ground parts of the plant. Lesions can be seen on the leaf collar, culm, culm nodes, and panicle neck node. Internodal infection of the culm occurs in a banded pattern. Nodal infection causes the culm to break at the infected node (rotten neck). It also affects reproduction by causing the host to produce fewer seeds. This is caused by the disease preventing maturation of the actual grain.
The pathogen infects as a spore that produces lesions or spots on parts of the rice plant such as the leaf, leaf collar, panicle, culm and culm nodes. Using a structure called an appressorium, the pathogen penetrates the plant. The appressorium cell wall is chitinous and its inner side contains melanin. which is necessary to damage host structures. The turgor pressure generated during this process is sufficient to penetrate the plants' cuticles routinely, and experimentally can penetrate Kevlar. This impressive turgor is produced by synthesis of glycerol and maintained by the aforementioned appressorial melanin. The pathogen is able to move between the plant cells using its invasive hyphae to enter through plasmodesmata. M. grisea then sporulates from the diseased rice tissue to be dispersed as conidiospores. After overwintering in sources such as rice straw and stubble, the cycle repeats.
A single cycle can be completed in about a week under favorable conditions where one lesion can generate up to thousands of spores in a single night. Disease lesions, however, can appear in three to four days after infection. With the ability to continue to produce the spores for over 20 days, rice blast lesions can be devastating to susceptible rice crops.
Infection of rice induces phosphorylation of the light-harvesting complex II protein LHCB5 . LHCB5 is required for a reactive oxygen species burst produced by the host which provides resistance against this pathogen.
Rice blast is a significant problem in temperate regions and can be found in areas such as irrigated lowland and upland. Conditions conducive for rice blast include long periods of free moisture and/or high humidity, because leaf wetness is required for infection. Sporulation increases with high relative humidity and at 25–28 °C (77–82 °F), spore germination, lesion formation, and sporulation are at optimum levels.