Home • Magnaporthe oryzae 70-15 v3.0
Rice blast disease caused by Pyricularia sp.
Rice blast disease caused by Pyricularia sp.
Image Credit: O.P. Sharma, from Bugwood.org used under a Creative Commons Attribution-Noncommercial 3.0 License.

Magnaporthe oryzae (syn. Pyricularia oryzae, syn. Magnaporthe grisea)

The genome sequence and gene prediction of Magnaporthe oryzae 70-15 have not been determined by the Joint Genome Institute (JGI), but were downloaded from NCBI on Aug 1, 2019. In order to allow comparative analyses with other fungal genomes sequenced by the JGI, a copy of this genome is incorporated into Mycocosm. Please note that this copy of the genome is not maintained by NCBI and is therefore not automatically updated. JGI tools were used to automatically annotate predicted proteins.

Commonly known as rice blast fungus, rice rotten neck, rice seedling blight, blast of rice, oval leaf spot of graminea, pitting disease, ryegrass blast, and Johnson spot, Magnaporthe grisea is a plant-pathogenic fungus 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. 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 this 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.

Like many foliar plant pathogens, M. oryzae is well adapted to attack and penetrate its host. All aerial parts of the plant are subject to invasion, but losses are most devastating when the panicle or node at the base of the panicle is infested and killed resulting in loss of grain set. 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 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.

Management of rice blast disease is most precarious. While in the past, control was mainly through use of expensive and potentially hazardous chemicals (when affordable) the focus has shifted, as it has for most diseases, to more environmentally friendly and potentially less expensive approaches, principally mediated through host resistance. The rice blast genome appears to be quite unstable and in some instances new races appear relatively quickly. A key to developing effective and durable resistance is through a comprehensive understanding of the host-pathogen interaction, which in turn requires a thorough understanding of both the host and the pathogen.

Magnaporthe oryzae is an excellent model organism for studying fungal phytopathogenicity and host-parasite interactions. M. oryzae is a haploid, filamentous Ascomycete with a relatively small genome of ~40 Mb contained in 7 chromosomes. The majority of fungal pathogens belong to this taxonomic class or exist as related asexual forms. M. oryzae is also closely related to the non-pathogen Neurospora crassa, a leading model organism for the study of eukaryotic genetics and biology. Unlike many phytopathogenic fungi such as mildews and rusts, the rice blast fungus can be cultured on defined media, facilitating biochemical and molecular analyses. Significantly, early stages of the infection process including germination, appressorium formation and penetration can be studied ex-planta.

Genome Reference(s)