Phenotypic stability in Cultivated Gossypium

Abstract

Results are reported from experiments designed to test the effects of ploidy and level of heterozygosity on the phenotypic stability of certain relatively inbred lines of cotton (Gossypium) and F� hybrids derived from all possible combinations among these lines. The mode of gene action and the role of heterosis in relation to phenotypic stability also were studied and the results made a part of this dissertation. The experimental materials consisted of four reasonably productive and near-inbred lines from each of three cultivated species: an Old World diploid (G. arboretum L.), and two New World allotetraploids (G. hirsutum L. and G. barbadense L.). Fifteen phenotypic characters or traits were measured in five different environments. In each environment, the inbreds and their F� hybrids were grown in two randomized-blocks, divided into split-plots. Since inbreds and their F� hybrids were used, genetic variance was minimized and only environmental variances were analyzed. Phenotypic stability was estimated by using both macro-and microenvironmental variances. Macroenvironmental variances were calculated as the deviation of species and line means from the overall environmental mean. Microenvironmental variances were the within-plot variances associated with the deviations of individual plant measurements from the plot mean. Analysis of the data showed that the level of ploidy had little, if any, effect on phenotypic stability; the diploid species buffered environmental fluctuations as well as did the allotetraploid species. Furthermore, when analyzed in like manner, the inbred lines proved to be as stable phenotypically as the F� hybrids. The variability observed among the different environments showed no definite trend or set pattern in either the inbred or the F� hybrids, which suggested that the stability measured was random in expression..