Rice (Oryza sativa) belonging to the family Graminae and subfamily Oryzoidea is the staple food of the world’s population and occupies almost one-fifth of the total land area covered under cereals. It is grown under diverse cultural conditions and over a wide geographical range. Most of the world’s rice is cultivated and consumed in Asia, which constitutes more than half of the global population [1]. In all rice growing areas the blast disease is the most serious fungal disease causing heavy yield losses from 10% to 80% [2]. The rice blast disease is caused by the fungus Pyricularia grisea, which, in its sexual state, is known as Magnaporthe grisea (Hebert) Barr. (anamorphe: Pyricularia grisea Cav.), a filamentous heterothallic ascomycoteous fungus. The rice blast is one of the most devastating diseases of rice and often reduces rice yields greatly in rice-growing countries under disease-conducive conditions. The disease can strike all aerial parts of the plant. Most