Blast disease, caused by the fungal pathogen Magnaporthe
grisea (Herbert) Borr. (anamorph Pyricularia oryza Cav.), is
one of the most devastating diseases of rice, reducing yield up
to 10 billion kilograms annually worldwide (Zeigler et al.
1994). Since the early 1950s agricultural chemicals have beensynthesized for blast disease control; however, excessive
applications of agrochemicals can pose a threat to human
health and the environment. The use of resistant cultivars with
major resistance (R) genes still remains one of the most reliable
methods to manage the diseases. Identification and incorporation
of different blast resistance genes with overlapping
resistance spectra have long been the main objectives of rice
breeding programmes worldwide