study on the effects of blast disease (pyricularia oryzae) on yield of rice under field condition

blast disease of rice caused by pyricularia oryzae is a potentially damaging disease in northern due to planting of susceptible local cultivars and favorable conditions. to assess the effects of blast on rice yield components and yield loss, one field experiment was conducted at the lowland culture conditions. analysis of blast effects on rice indicated that the maximum yield losses due to unprotected treatments at vegetative, reproductive and both stages were 4.72, 6.39 and 14.41% respectively. node blast had more influence than neck blast in decreasing the 1000-grain weight and number of filed grains and in increasing the number of unfiled grains per panicle. yield losses due to blast were correlated either to percentage of leaf blast (lb) or percentage of neck, node and panicle blast (nnpb) in unprotected treatments at vegetative stage in each two years of 2009 (for lb, r= 0.868, p. value= 0.00517; for nnpb, r= 0.848, p. value= 0.00775) and 2011(for lb, r= 0.785, p. value= 0.0211; for nnpb, r= 0.801, p. value= 0.0169). also two positive significant correlations were observed between lb % and nnpb% in 2009 (r= 0.882, p. value= 0.00376) and 2011 (r= 0.812, p. value= 0.0143) in this treatment. whereas, in unprotected treatment at reproductive stage yield loss was correlated only to percentage of nnpb (r= 0.918, p. value= 0.0013).