SUPPRESSION OF RICE BLAST BY PREINOCULATION WITH AVIRULENT PYRICULARIA-ORYZAE AND THE NONRICE PATHOGEN BIPOLARIS-SOROKINIANA

Avirulent isolates of Pyricularia oryzae and isolates of Bipolaris sor okiniana, a nonrice pathogen, were used to suppress rice blast caused by P. oryzae. In greenhouse experiments, both fungi substantially redu ced leaf blast when applied 24 h or more before the pathogen. B. sorok iniana, but not avirulent isolates of P. oryzae, systemically reduced disease in leaf 5 when applied to whole plants at the four-leaf stage. In field experiments, both fungi were able to reduce neck blast signi ficantly. No increase in grain yield was obtained by using avirulent i solates of P. oryzae, whereas five sprays with B, sorokiniana from see dling to heading stages increased the grain yield in two of three expe riments conducted at two locations in Nepal. The significant increase in yield was observed under high inoculum pressure of P. oryzae. Induc ed resistance is suggested to be involved in the suppression of diseas e.