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Quantitative Genetics of Agronomic and Nutritional Traits in Related Grain Sorghum Random-mating Populations as Affected by Selection¹

Two related populations (NP20BR-ME and NP20BR-MEYD) of sorghum [Sorghum bicolor (L.) Moench] that were developed by one cycle of mass selection with the objectives of increasing metabolizable energy (ME) and metabolizable energy yield (MEYD), respectively, were evaluated for the effect of selection on and the relationships between agronomic and nutritional traits. Estimates were obtained from random S₁ families from each population in a replications-in-blocks design. The means of the two populations did not differ statistically for any agronomic or nutritional trait and had similar estimates of genetic variances that revealed large genetic variation for agronomic traits but relatively little for nutritional traits. Mostraits had significant genotype x year interaction variances. Broad-sense heritabilities for all traits were relatively high (0.44 to 0.92), had low standard errors (0.10 to 0.12), and were similar in both populations. Predicted gains from 20% selection intensity were 18.2 and 15.9% of the population means for grain yield in NP20BRME and NP20BR-MEYD, respectively. Expected gains for ME were small, and sometimes negative, whether selection was for yield, ME, or MEYD. Directional selection for grain yield alone or for ME alone would not be expected to result in simultaneous improvement of grain yield and ME, but selection for high MEYD should result in yield improvement equivalent to selection for grain yield alone with similar reductions in most nutritional traits negatively correlated with grain yield.

Key Words: Genetic parameters • Grain quality • Mass selection • Metabolizable energy • Metabolizable energy yield • S₁ families • Sorghum bicolor (L.) Moench

² Former graduate research assistant (now assistant agronomist, Dep. of Agronomy, Mississippi State Univ., Mississippi State, MS 39762 assigned to CIAT, Apdo. Aereo 6713, Cali, Colombia); research geneticist, USDA/ARS; and professor, Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583.

Received for publication November 13, 1984.