Mutagenesis Mechanism Of Space Mutation And Its Breeding Application In Rice

Space mutation breeding provides a new and effective way for deveopling new crop varieties and elite germplasms. In this study, the radiosensitivity and mutagenic effects were studied using24rice cultivars differing in eco-types by treatments of space mutation and Co y-irradiation. The breeding process of a late Japonica rice variety Hangtian36with early-maturing and high grain quality was used as an example to illustrate the successful application of space mutation in rice breeding. The main results are as follow:1. There is an obvious difference in the sensitivity and effect of space mutagenesis among the examined rice cultivars. Radiosensitivity was expressed based on the total physiological damage or stimulus of seedling height and seed setting rate in M1generation, and mutations of plant height and heading date in M2were observed. The results indicated that japonica rice had stronger radiosensitivity of space environment mutation and y-irradiation than indica rice, bred cultivars stronger than landraces, medium-late indica and late indica stronger than early indica whereas no significant differences among different japonica climate ecotypes.2. The difference exists in mutagenesis effect of rice between space mutation and y-irradiation. Most rice cultivars with non-sensitive to y-irradiation were also non-sensitive to space mutation and only the one-fourth of cultivars sensitive to y-irradiation showed radiosensitivity to space mutation. Space flight had obvious stimulus effects on seedling growth for54.2%cultivars. In M2generation, mutations of plant height and heading date could be induced by both space environment and y-irradiation, but the mutation frequencies differed between these two mutagenesis treatments. There were significant correlations between the total physiological damage in Ml and the mutation frequencies of dwarfing, high plant and early maturity in M2after space flight. The results suggest that mutagenic mechanisms may be different between space environment and y-irradiation.3. A new rice variety Hangtian36developed from space mutagenesis showed multi-traits being improved. An early-maturing late Japonica rice variety, with high grain quality and disease resistance, was developed from the mutated progeny of Bing1067treated by carrying its seeds with a recoverable satellite. Hangtian36has advantages over the original variety Bing1067in mature duration, grain quality and blast resistance. It has strong tolerant ability to late sowing. So it is an ideal variety suitable for the use of emergency situation, such as in the natural disaster years resulting from typhoon. The successful breeding of Hangtian36showed that space mutation is an effective method of simuhaneous improvement for multiple traits of rice.