EFFECT OF WHEAT CULTIVAR MIXTURES ON SPOT BLOTCH (BIPOLARIS-SOROKINIANA) AND GRAIN-YIELD

Two experiments were conducted at Rampur, Nepal, in the 1990-1991, 199 1-1992, and 1992-1993 growing seasons (November to April) to study the effect of mixtures of wheat (Triticum aestivum L.) cultivars on the s everity of spot blotch caused by Bipolaris sorokiniana (Sacc. in Sorok .) Shoem. The first experiment involved using a mixture of equal weigh ts of seed 'RR 21', 'UP 262', and 'Nepal 251', while the second experi ment involved using equal weights of seed of 'RR 21', 'UP 262', and 'N epal 297'. RR 21 is highly susceptible to spot blotch, whereas the oth er cultivars are somewhat less so. Data were recorded for area under t he disease progress curve (AUDPC), grain yield, number of spices per u nit area, kernels per spike, and hundred kernel weight. AUDPC in the s ix trials was significantly (p < 0.05) reduced by 9 to 57% in the mixt ures compared to the average of the component cultivars. Mixtures incr eased yields 5.1 to 8.6% (p < 0.05) over the average of the component cultivars in five of the eight trials. There was no change in grain yi eld components in the mixtures versus those in component cultivars. Th e results suggest that mixtures of wheat cultivars with different leve ls of resistance to spot blotch offer an alternative strategy of manag ing spot blotch at the farm level.