Department of Plant Breeding, Punjab Agricultural University, Ludhiana
*A part of the work submitted by S. S. Saini for the Ph.D. Degree (Plant Breeding) of the Punjab Agricultural University; the abstract of the present paper was presented to Indian Science Congress at its 56th Session held in January, 1969 at Bombay.
Dry seeds of two rice varieties viz., Jhona-349 of Punjab and Taichung (Native)-1 of Taiwan, and F2 of crosses between them were treated with 20 kr, 30 kr, 40 kr and 50 kr of gamma rays from a Co60 source. To study the variability in R2 generation, space plant rows from 40 randomly selected R1 panicles of each treatment and the respective controls, were grown in a split plot design with three replications. Data were recorded for earing date, plant height, tillers and yield per plant on five randomly selected plants in each row.
The mean value of a character in 38 out of 48 treated populations remained unchanged inspite of increase in the variance while in the remaining 10 cases it recorded significant and unidirectional shift from that of the control. The genetic variance in the hybrid material was greater in magnitude than that obtained in the pure types for all the characters; and except for tillers per plant it further increased after irradiation, showing a supplementary effect to the variance normally released by hybridization. The heritability estimates and genetic gains also followed the same trends. The maximum expected genetic gain was 74.17% for yield in the hybrid material treated with 20 kr.
The range of individual plant values expanded after irradiation with one or more d.oses and for maximum increase different dose was required for different characters in different genotypes. Thirty mutants with extreme values, not available in the original populations, were isolated and some of them had good combination of useful characters and plant type for growing under condition of high fertility. The frequency of such variants was higher in the treated than in the untreated hybrid material and the treated pure types.
It was concluded that for effecting improvement in various economic characters of rice plant, hybridization followed by irradiation may be better than hybridization alone.
