Gene action and selection indices in two cotton (Gossypium barbadense L.) crosses

摘要

The main objectives of this study were to estimate the type of gene action, genotypic correlation, path coefficient analysis and classical selection index for yield, yield components and earliness characters in two intraspecific cotton crosses (Family 8/87 X Soviet variety S-6037 and Giza 80 X S-6037). P1, P2, F2 plants and F3 families for the two crosses were cultivated in an experiment with three replications. Data were recorded on cottonseed yield/plant, bolls/plant, boll weight, lint percentage, seed index, earliness index and position of the first fruiting node. Additive variance was the main component of the genetic variance for cottonseed yield/plant, bolls/plant, seed index in the first cross and position of the first fruiting node in twocrosses. Both additive and dominant genetic variance were controlling boll weight, lint percentage and earliness index in the two crosses, and seed index and earliness index in the second cross. Dominance variance was controlling cottonseed yield/plant and bolls/plant in the second cross. High narrow sense heritability estimates in F2 populations were detected for bolls/plant and seed index in cross 1. High narrow sense heritability estimates for F3 family means were detected for cottonseed yield/plant,and boll weight in the first cross, and seed index and position of the first fruiting node in the two crosses. A high percentage of response to selection was detected in the F2 population for bolls/plant, boll weight and seed index in the first cross. Ahigh percentage of response to selection was detected in F3 family means for cottonseed yield/plant, boll weight and the earliness index in the first cross, lint percentage in the second cross, and seed index and position of the first fruiting node in two crosses. In cross 1, there was a highly significant positive genotypic correlation between cottonseed yield/plant and each of bolls/plant and boll weight, while the earliness index was negative and highly significant. The genotypic correlation betweenearliness index and bolls/plant was negative and highly significant, while the correlation between the earliness index and each of boll weight and lint percentage was positive and significant. In cross 2, there was a highly significant positive genotypic correlation between cottonseed yield/plant and bolls/plant. Path coefficient analysis showed that bolls/plant had the highest direct effect on cottonseed yield/plant in the two crosses. Minor values for indirect effects through the other characters inthe two crosses were detected. The best five families determined by the classical selection index were retained for culture in the next generation.