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Variability for Yield and Yield Components in IAP1R Grain Sorghum Random-Mating Population. I. Means, Variance Components, and Heritabilities¹

Genetic variability of the random-mating sorghum [Sorghum bicolor (L.) Moench] population IAP1R was evaluated in seven environments. Three cycles of gridded mass selection for grain yield of individual plants had been completed in the population. One-hundred-twenty half-sib and 120 S₁ families chosen randomly from the C3 were included in Exp. I at Ames (central Iowa), and another sample of 120 S₁ families was grown in Exp. II at Ames and Castana (western Iowa). Estimates of inbreeding depression at 100% homozygosity were –13.6% for grain yield, –6.3% for seeds/panicle, and –4.9% for 100-seed weight; indicating that heterotic effects were relatively important in the expression of yield, of moderate impact on seed numbers, and small for seed size. Genotype-environment variances for yield were low for half-sib and S₁ families in the Ames 1978 through 1980 environments (Exp. I), and progeny mean estimates of broad-sense heritability were high (0.84, 0.85). Heritabilities these environments also were moderate to high for the components of yield; 0.76, 0.79 for seeds per panicle, 0.74, 0.82 for 100-seed weight, and 0.63, 0.66 for panicles per plant. S₁ families at Ames and Castana 1981-1982 (Exp. II) displayed large genotype- environment variance for yield, and its heritability was 0.74. Heritabilities in Exp. II were 0.80 for seeds per panicle, 0.78 for 100-seed weight, and 0.77 for panicles per plant. Individual plant estimates of heritability in the two experiments were low for grain yield (0.13, 0.06) and seeds per panicle (0.20, 0.23). Heritability estimates of 0.41 and 0.43 for 100-seed weight, however, suggested that improvements in seed size should be possible by using gridded mass selection.

Key Words: Sorghum bicolor L. Moench • Recurrent selection • Genetic male-sterility • Mass selection

² Former graduate assistant, now postdoctoral fellow, maize program, CIMMYT, El Batan, Mexico; professor of agronomy, Iowa State Univ., Ames, IA 5001I; and former research geneticist, USDA-ARs, AR, Ames, IA 50011, now statiscal geneticist, Pioneer Hi-Bred Int., Johnston, IA 50131.

Received for publication April 23, 1984.