Polygenic Variation Following Irradiation in Interspecific Crosses of Cotton

Interspecific crosses in Gossypium both hattheiploid and detraploid level mostly fail to yield desirable recombinants owing to a rapid reversion of the hybrid population to one or the other of the parental genotypes. The present study as undertaken to assess the possibility of widening the spectrum of recombination through F₁ seed irradiation. F₁ seeds of the crosses between Gossypium arboreum and G. herbaceum and between G. hirsutum and G. barbadense were exposed to an acute dose of Co⁶⁰γ-rays. A comparative assessment was made of the variability occurring in the regular F₂ progenies and in the progenies derived from irradiated F₁ plants. The range of the distribution of plot means was invariably wider in the treated population for almost all the characters in comparison to their respective controls. The analysis of variance showed higher values for all the characters in the treated populations as compared to control. However the precise effect of radiation in inducing variability varied from character to character. Data on the coefficient of genetic variability showed in general increased values in the irradiated diploid and tetraploid crosses but the magnitude of variability was considerably higher in the former than in the latter. Scope for selection thus exists.

The increased variability has mainly been attributed to micro-mutations. However, the occurrence of rare types of segregants for several important characters supports the possible role played by recombinations at meiotic and somatic levels.