Mutagenic Effects of Gamma Radiation on Rice

Abstract

1. Dry grains of rice (variety Tjeremas of the indica type of Oryza sativa L., n = 12) were exposed to gamma radiation at dosages of 20, 25, 30, 40 and 50 Kr. Progenies of selfed normal and aberrant plants were grown for several generations to detect variations. 2. Dosages of 20, 25 and 30 Kr did not greatly reduce the percentage of germination while 40 and 50 Kr killed most of the seeds. Seedling survival was markedly reduced following 30 and 40 Kr, while no seedlings survived following 50 Kr. 3. Seedling height was reduced following dosages of 30 and 40 Kr, the plants having only 40% and 20%, respectively, of the height of the controls, while following 20 and 25 Kr, reduction in height was not great. 4. Of twenty-three R1 variations, seven mutations were isolated and established in R4 and R5 generations, namely, albina, xantha, striped, bushy, spreading, slow-grower, and long awn. The chlorophyll-deficiency mutations and long awn have occurred spontaneously as gene mutations in other varieties but spreading and slow-grower have not been reported. The latter mutants and bushy are promising stocks for rice improvement. 5. The only chromosomal aberration found in progenies of treated plants was heterozygous reciprocal translocation, recognizable by rings or chains of four chromosomes at metaphase I. A maximum of three interchange configurations per cell was observed in highly sterile lines, indicating the possible breakage of up to 50.0% of the bivalents of the complement.