Effect of wheat cultivar mixtures on spot blotch (Bipolaris sorokiniana) and grain yield.
Two experiments were conducted at Rampur, Nepal, in the 1990/91, 1991/92, and 1992/93 growing seasons (November to April) to study the effect of mixtures of wheat cultivars on the severity of spot blotch caused by Bipolaris sorokiniana [Cochliobolus sativus]. The first experiment involved using a mixture of equal weights of seed of cv. RR 21, UP 262, and Nepal 251, while the second experiment involved using equal weights of seed of RR 21, UP 262, and Nepal 297. RR 21 is highly susceptible to spot blotch, whereas the other cultivars are somewhat less so. Data were recorded for area under the disease progress curve (AUDPC), grain yield, number of spikes per unit area, kernels per spike, and hundred kernel weight. AUDPC in the six trials was significantly (p<0.05) reduced by 9 to 57% in the mixtures compared to the average of the component cultivars. Mixtures increased yields 5.1-8.6% (p<0.05) over the average of the component cultivars in five of the eight trials. There was no change in grain yield components in the mixtures versus those in component cultivars. It is suggested that mixtures of wheat cultivars with different levels of resistance to spot blotch offer an alternative strategy of managing spot blotch at the farm level.