Gene action in intervarietal diallel crosses of upland cotton Gossypium hirsutum L

Abstract

A complete diallel cross consisting of all possible F₁ hybrid combinations among 9 selected cotton varieties and their corresponding F₂'s were studied using a split-plot design with four replications. Data were taken on yield and its components, various fiber properties, and other agronomic characters. The objectives of this study were (i) To investigate the genetical bases of heterosis and inbreeding depression, (ii) To gain a better understanding of the nature of gene action involved in controlling quantitative characters, and (iii) to measure the phenotypic stability among the parents and their crosses. Heterosis, measured as deviation from the average mid-parent value, was consistently observed for most of the characters studied, but it was at low level. Inbreeding depression, calculated as F₂ reduction below F₁ performance, was significantly different from zero for all the characters except fiber properties. Griffing's combining ability analysis and Hayman's diallel cross techniques were used to obtain an estimate of the genetic parameters. General and specific combining ability effects were both highly significant for all the characters, however, the additive gene effects were more greater than nonadditive gene effects. The diallel analysis showed that all the characters were within the range of partial dominance and that all polygenetically inherited characters. The results showed that heterosis was due to dominant and/or epistatic gene action. Some of the characters met all the requirements for the diallel analysis. However, over-all epistasis was found in plant height, earliness, boll size, and no. of bolls/plant. Multiple allelism and possibly correlated gene distribution appeared to be present in the days to first flower, seed index, lint %, no. of seeds/boll, and yield. The study of phenotypic stability in cotton showed that there was no developmental homeostasis associated with F₁ hybrids and that stability was under genetic control, exhibited partial dominance and it was under the control of polygenic system.