EVALUATION OF SORGHUM HYBRID MIXTURES FOR CONTROLLING SORGHUM LEAF-BLIGHT

This is the first report on the use of mixtures of sorghum genotypes to control a major pathogen. The effect of mixtures of sorghum hybrids on development of sorghum leaf blight caused by Exserohilum turcicum was studied in three locations in central Mexico. Seed of resistant and susceptible sorghum hybrids were mixed in resistant:susceptible ratios of 1:0, 3:1, 1:1, 1:3, and 0:1. Some disease developed on the resistant hybrid, but disease severity varied little on the resistant component of mixtures in any location. Only in one location was disease severity on the resistant hybrid observed to significantly increase with increasing proportion in the mixture (P < 0.05). This increase, however, was more than compensated for by reduction in disease severity in the susceptible hybrid. In contrast, there were significant differences in the amount of diseased tissue on the susceptible hybrid (P < 0.05) as the percentage of the resistant component was increased in all locations. Although disease amelioration was more noticeable in locations with higher disease pressure, it was significantly greater under conditions of low disease incidence. Every addition of 1% of resistant plants to the susceptible plant population significantly reduced disease development by up to 0.4% on the susceptible hybrid (P < 0.05). Furthermore, mixtures had a significant effect on yield of the susceptible hybrid but not on yield of the resistant hybrid. Adding 1% of resistant plants to the mixture increased yield of the susceptible plant by up to 0.55%.