RECOMBINATION IN MAGNAPORTHE GRISEA

Abstract

The heterothallic ascomycete, Magnaporthe grisea, is the blast pathogen of rice and about 50 other grasses, and has potential for sexual and asexual reproduction. In most populations, data from mating type, fertility assays, and genotypic diversity strongly suggest that the pathogen is asexual. However, parasexual recombination cannot be ruled out. Chromosome length polymorphisms and translocations may prevent successful meiosis in most populations. Pathogens of millets and some grasses growing with rice appear to be largely genetically isolated, though some gene flow may occur. Sexual fertility has repeatedly been reported in rice pathogens from mountainous regions of South and East Asia. Several means by which sexual fertility may be lost in an agricultural setting are advanced.

Clonality and Recombination in Genetically Differentiated Subgroups of Cryptococcus gattii

“…In addition, molecular studies reveal some purportedly asexual species to possess a recombining population structure, indicating that cryptic sex occurs via an unknown mechanism (5,13,39,47). Some fungal species do appear to be genuinely asexual, but as most fungi can release asexual propagules, often in large numbers, under favorable conditions, the possibility remains that clonality is restricted to the population under study, and a sexual population of the same species occurs elsewhere (11,48).…”

Biogeographic range expansion into South America byCoccidioides immitismirrors New World patterns of human migration

“…Such introductions have been well documented, for instance, Phytophthora infestans into Irish potato agriculture (1), Cryphonectria parasitica in the American Chestnut tree (2), and Magnaporthe grisea in non-Asian rice (3). Introductions are associated with founder effects that dramatically alter a pathogen's genomic structure by reducing variability and increasing linkage (4,5).…”

Magnaporthe oryzae Genetic Diversity and Its Outcomes on the Search for Durable Resistance

“…Both of them are essential for sexual recombination (Kang et al, 1994). M. oryzae isolates can be hermaphrodite, male fertile or sterile, but crossing only occurs between fertile isolates from different mating types, and when at least one isolate is hermaphrodite (Zeigler, 1998). Many studies were conducted in order to evaluate the frequency of the different mating types around the world.…”

“…One reason could be the founder effect, because when rice culture was introduced in a new area, probably only one mating type was established (Zeigler, 1998). It is also possible that in some cases the MAT locus could be linked to an avirulence gene, with no compatibility with the prevailing Rice cultivar, and this could represents a drawback for fitness (Notteghem & Silue, 1992), being eliminated along time.…”

“…When rice is cultivated on areas where the weather conditions enable the fungi to survive on a mycelia form during many fallow seasons, mutations that remove sexual reproduction could be fixed because of high energy costs of this character. It is also possible that rice was introduced in worldwide areas where weather conditions would be adverse for sexual reproduction occurrence (Zeigler, 1998).…”