Mutational analysis of embryo differentiation in rice

Abstract

Rice seeds were treated with two doses each of EMS and gamma rays. The tillers in the M: generation were classified according to their ontogenic relationship. The M2 generation was raised as M1 ear progenies. Seedlings were scored for chlorophyll and other seedling mutants. The cluster sharing frequencies for mutations i. e.x the frequency with which two M( ears segregated for identical mutations were determined by pair wise comparisons. The following conclusions were drawn. The frequencies of emergence of various categories of tillers are different. Tillers in the axils of the coleoptile and the first primary leaf do not normally develop. The frequencies for primary tillers increase upto the fourth and thereafter gradually decrease. Analysis of the frequencies of cluster sharing reveals that the primary tiller prirnordia upto the fifth have already differentiated from the main shoot primordium in the rice embryo. Thus there are at least six mutally exclusive mutant sectors which do not share a mutation in common. Independent mutant sectors are not detected within primary groups. A diagramatic representation of the tillering system in rice indicating mutant clusters is presented. The diagram provides information on cluster sharing frequencies of mutations and gives an idea of the degree of differentiation in the dormant rice embryo. The present study indicates that from the point of view of recovery of mutations, it is necessary to provide optimum conditions to facilitate the development of the lower primary ears in the M, plants. It is also important to collect all the primary ears upto the fifth besides the main ear from the M1 plants for raising the M2 generation in order to recover all the mutations induced.