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.