Genetic Control for Percentage Grain Protein and Grain Yield in Grain Sorghum

Inheritance of grain protein and yield was investigated in grain sorghum [Sorghum bicolor (L.) Moench]. Divergent selection was applied to a series of individual plants from the breeding nursery for high and low protein content. Protein percentage was determined from a random sample of finely ground grain by the Udy dye-binding method. The selected lines were crossed onto A-lines ‘Martin’ (high protein) and ‘Wheatland’ (low protein). Test crosses, parents, and checks were planted in replicated lattice-designed tests at Clovis, N.M., for 3 years. Highly significant differences were detected between the lines selected for high and low protein content for both percentage of grain protein and grain yield. Significant differences also were found between the two female lines. Genetic analyses of the test crosses and their parents indicated that low protein content was partially conditioned by dominant genes. Of 155 test crosses, 3% produced grain protein content significantly below the lower parent, indicating negative heterosis; 35% of the test crosses were signifidcantly below their mid-parent mean, indicating dominant genes for low protein. Grain yield was determined by dominant or overdominant gene action as 43% of the test crosses yielded significantly above their midparent mean, and 35% of the crosses yielded significantly more than the highest yielding parent. Protein percentage had a highly significant negative correlation with yield (r = -0.53, significant at the 0.01 level). Partitioning of the genetic variance indicated that additive gene action was more important than nonadditive gene action for both attributes studied. The genetic variances for males were greater than for females for both attributes; however, many more males were tested than females. Narrow-sense heritability values of 35 and 44% were computed for grain protein percentage and yield, respectively.