Variation and covariation of seed weight and its components in wheat following irradiation, EMS, and hybridization

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Abstract
Seeds from two hexaploid wheat varieties, ‘Giza 150’ and ‘Sonora 64’, and the F2 seeds of their hybrid were given two mutagenic treatments, gamma irradiation and ethyl methanesulfonate (EMS), to study the type of variation and covariation in seed weight, width, and length induced by irradiation, EMS, and hybridization. Measurements of seed weight and its components were taken on 30 replicated lines derived from each treated and non-treated material. Both irradiation and EMS produced significant variability in seed weight and its components in the pure genetic background. The hybrid genetic background somewhat depressed the expression of irradiation-induced variability. The variations resulting from EMS and hybridization were to a great extent independent and cumulative. Neither EMS nor irradiation caused any significant shift in the means of seed weight, width, and length. The positive association between inheritance of width and length in irradiation-derived materials did not increase the mean seed weight compared with the control. The magnitude of the genetic correlations in irradiation varieties was double that obtained from hybrid-or EMS-derived materials. It is suggested that EMS mainly produced mutations of genes and/or minute chromosomal aberrations, whereas the genetic variation produced by gamma irradiation was accompanied by the loss and/or gain of large segments of the chromosomes.