Grain Sorghum Resistance to Midge by Yield Loss vs. Visual Scores

Abstract

Biology of the sorghum midge, Contarinia sorghicolà (Coquillett), necessitates testing of sorghum, Sorghum bicolor (L.) Moench, cultivars in field plots in multiple locations and/or years to identify resistant genotypes. Using converted exotic sorghum cultivars, this study was conducted to compare visual damage scores across locations and years vs. indirect resistance measurements (percentage yield loss and number of midge per panicle) in a single location and year with two planting dates. Visual damage ratings were made at physiological maturity on the percentage of blasted kernels per panicle in replicated, randomized‐complete‐block field experiments at three locations in 1983 through 1985. In 1985, indirect measurements and visual damage ratings were made at one location. A significant positive relationship was found between visual midge damage rating and percentage yield loss (r = 0.347), and between visual midge damage rating and midge number (r = 0.220). Percentage yield loss did not increase the reliability of identification of resistant cultivars. Cultivars identified with resistance by both methods were IS8232C, IS8237C, IS8112C, IS2740C, IS3390C, IS7132C, IS2685C, IS957C, IS7193C, IS2144C, and IS12572C. The correlation between percentage yield loss and midge number (r = 0.090) was nonsignificant. Both methods depend on high midge density to differentiate resistant and susceptible genotypes. When midge were not abundant good differentiation was not obtained. Indirect resistance measurements were more time consuming than a single visual rating at maturity, and when multiple years or locations were required, the visual damage rating was a more effective method of germplasm evaluation.