An introduction to the phytopathogenic fungus Magnaporthe grisea
Magnaporthe grisea is a heterothallic, phytopathogenic ascomycete capable of infecting over 50 species of grass (Ou, 1985). The most economically important of the species infected by M. grisea is rice (Ou, 1985; Rossman et al., 1990), which is the staple diet of almost half the global human population. Rice blast disease, caused by M. grisea, is an extremely serious disease; despite modern advances, such as the development of fungicides and breeding of resistant rice cultivars, every year between 11% and 30% of the rice harvest is destroyed by this disease. A serious blast epidemic occurred in Bhutan in 1995 in which 1090 tonnes of rice was lost, with up to 100% crop losses for some farmers (Thinlay et al., 2000). The American Centre for Disease Control and Prevention has also classified rice blast disease as a significant biological weapon that could be deployed in acts of agricultural bioterrorism (Schaad et al., 2003).
Rice blast disease manifests itself as a number of different pathologies affecting stems, leaves and panicles of the rice plant (Talbot, 2003). Blast infections of stem nodes, for example, can cause the rice stem to rot before maturation of the seed and can result in complete loss of the rice crop (Ou, 1985). If leaves of rice seedlings are infected, a reduction in photosynthetic capacity can occur; growth is therefore impeded and seedlings often die.