23.Endosperm mutants of rice induced by N-methyl-N-nitrosourea treatment of fertilized egg cells

Plant Breeding Laboratory, Faculty of Agriculture, Kyushu University, Hakozaki, Fukuoka, 812 Japan

Several kinds of induced mutants for embryo or endosperm properties have been reported in rice recentry (Toda 1979; Amano 1981; Satoh and Omura 1981; Okuno et al. 1983; Yano et al. 1984). We maintain about 400 endosperm mutants of rice with several thousand morphological or physiological mutants, most of them induced by N-methyl-N-nitrosourea (MNU) treatment of fertilized egg cells. This method gives a high mutation frequency and little chimera formation (Satoh and Omura 1979). The spectrum of endosperm mutants made available in rice is now as rich as that in corn (Satoh and Omura 1981).

The frequency of various embryo and endosperm mutants induced by one-hour treatment with 0.75 mM MNU at different stages of fertilized eggs are given in Table 1. The frequency varied among types of mutation, being highest in the white core mutant, possibly reflecting the number of genes controlling each trait. The results of allelism tests supported this assumption. The mutation frequencies for certain types seemed to differ accordidng to the stages of treatment.

Table 1. The mutation frequency for embryo and endosperm properties induced by 0.75 mM MNU treatment for one hour at different hours after flowering

Gene analysis for these mutants indicated that most of them were controlled by a single recessive gene with the exception of two floury mutants, one controlled by a single dominant gene and the other by two recessive duplicate genes (Satoh and Omura 1981). All glutinous mutants examined were allelic to wx located on chromosome 6. All dull mutants except for one showing an intermediate glutinous-ordinary property, were controlled by genes independent of wx. There were at least four dull loci, and one of them, du-1, was located on chromosome 7. Genes for three high amylose mutants were at the same locus. Most of sugary mutants were controlled by the same gene, su, which was located on chromosome 12. There were at least two loci for shrunken mutants, one being located on chromosome 3 (Yano et al. 1984). Two loci were recognized for giant embryo mutants, one belonging to chromosome 10. There were many different loci for floury or white core mutants, one of which was located on chromosome 5.

Amano, E., 1981. Genetic and biochemical characterization of waxy mutants in cereals. Environmental Health Perspective, 37: 35-41.

Okuno, K., H. Fuwa and M. Yano, 1983. A new mutant gene lowering amylose content in endosperm starch of rice, Oryza sativa L. Jpn. J. Breed. 33: 387-394.

Satoh, H. and T. Omura, 1979. Induction of mutation by the fertilized egg cell with N-methyl-N-nitrosourea in rice. J. Fac. Agr. Kyushu Univ. 24: 165-174.

----- and ----- , 1981. New endosperm mutations induced by chemical mutagens in rice, Oryza sativa L. Jpn. J. Breed. 31: 316-326.

Toda, M., 1979. Breeding of new varieties by gamma-rays. Gamma Field Symp., 18: 73-82.

Yano, M., Y. Isono, H. Satoh and T. Omura, 1984. Gene analysis of sugary and shrunken mutants of rice, Oryza sativa L. Jpn. J. Breed. 34: 43-49.