Blast, caused by Pyricularia grisea Sacc., is a major disease of rice (Oryza sativa L.) in Nepal. It causes seedling loss (Chaudhary and Sah 1998) and adversely affects plant growth and yield (Chaudhary 1999). The fungus is highly variable, making disease management complicated. This study was undertaken to understand the variability of blast isolates in order to deploy resistance genes properly.
Diseased leaves were collected on diverse genotypes from different locations. Twenty-five monoconidial isolates were obtained and maintained in agar slants during 2000 following the procedures of Bonman et al (1986). Isolates were multiplied on prune agar plates and inoculated at 105 mL-1 on 3-5-leaf stage seedlings of 10 differential varieties in a greenhouse in 2001 (Table 1). The 10 seed- lings of each differential, replicated thrice, were raised in aluminum trays, filled with farmyard manure, and fertilized with 150-22-0 kg NPK ha-1.