Improvement of restorer and maintainer lines in rice (Oryza sativa L.) by gamma radiation

Abstract

Rice is a strictly self-pollinating crop. However, in hybrid rice seed production, an effective male sterility system is used to produce hybrid seed in bulk. In a hybrid rice system, the pollen grains of cytoplasmic male sterile (CMS) lines are sterile, and the female organ of the CMS depends on the fertile pollen released by the maintainer or restorer lines via out-crossing or cross-pollination to produce seeds. Floral traits and growth behavior of CMS and its corresponding maintainer and restorer lines are essential factors in hybrid rice seed production because they influence outcrossing or cross-pollination. Seeds of the 4 maintainer lines, or B lines, and the 5 restorer lines were treated with five gamma radiation doses: 0, 100, 200, 300, and 400 Gy, to study their mutagenic effect on the growth, yield, and floral traits of these rice genotypes, as well as to induce genetic variability for selecting plants with desirable characters. Results showed that all growth, yield, and floral traits studied in the M1 generation decreased steadily with increasing doses of gamma rays when compared to the control. The dose of 300 Gy recorded the highest mean values for some growth, yield, and floral traits studied in the M2 generation when compared to the control. The genotype-dose interaction was significant and highly significant for all growth, yield, and floral traits studied in M1 and M2 segregating generations except for anther width in the M1 generation, which indicated that the tested genotypes varied from treatment to treatment. The highest values for growth and yield traits were recorded when using Giza 178, Giza 182, and the IR 58025B mutant with 300 Gy of gamma rays in the M2 segregating generation. And the highest values for floral traits were recorded when using Giza 182 and the IR 70368B mutant with 300 Gy of gamma rays in the M2 segregating generation. The measurements of variation were, in general, higher in the treated plants at M2 generation. High heritability coupled with high genetic advance as percent of the mean was recorded for most studied traits, suggesting the improvement of these characters through simple phenotypic selection. Used irradiation by gamma-ray exhibited different genetic variability for the development of restorer and maintainer lines, such as desirable plant height, early heading, and high yield plants. Also, improving floral traits such as the length and width of anthers, percentage of pollen fertility, number of pollen grains per anther, total stigma length, and stigma width