Studies on the utility of artificial mutations in plant breeding. : IV. Aberrations in the progeny of rice plants exposed to X-rays at several developmental stages.

Abstract

In thc previous paper of this series (Yamagata and Syakudo 1963b), it was reported that radiation injuries observed on the X-irradiated plants varied with the dose of X-rays and the developmental stage of plants at the irradiation. In the present study, the progeny (X2) of the irradiated plants was examined to obtain information on effective incduction of mutations. The seeds obtained from the long-day treatment section in 1961 were mainly used. The X1 panicles of each irradiated group ( I to V) were further classifred into "developmental-stage groups" based on the nunrber of days required for heading after irradiation. ( 1 ) The decrease of sprouting ability of X2 seeds obtained from X1 panicles irradiated with high doses (more than 10kr) of X-rays at postmeiotic stages was gleatel than at premeiotic stages. Almost no sprouting was observed in the seeds from X1 panicles irradiated with 20kr after meiosis. It was revealed however, that low-dose (1kr) irradiation at some stages before meiosis caused remarkabiy low sprouting abilities. ( 2 ) In the X2 generation, there were observed chlorophyll mutant seedlings such as albina, xan-tha, and viridis ; partially or complctely sterile plants ; early or late maturing plants ; tall or dwarf plants ; and plants with slender or round glumes, etc. i ) The frecluencies of the above mentioned aberrants tended to increase linearly with the dose of X-rays irrespective of irradiated stages. ii ) The frequencies of sterile X2 plants were ten times higher in the X1 panicles irradiated after meiosis than in those irradiated before meiosis. Unexpectedly, the frequencies of chlorophyll mutants and other aberrants did not vary with the developmental stages of X1 panicles at the irradiation. iii) No specific relations were found between the aberration spectrum in X2 and the developmental stage of X1 panicle at the irradiation or the kind of X1 injury. The possible cause of anomalous sprouting due to low-dose irradiation has been discussed, and the frequency and spectrum of induced aberrations examined from the viewpoint of plant breeding.