Seeds of five rice bean varieties viz. RBL-1, BRB-4, PRR-9302, PRR-2 and RBL-50 were
treated with 40 kr. dose of Gamma-rays. Distribution parameters like mean, range, variance,
skewness and kurtosis were estimated in the parental and M2 populations for six traits – plant height,
clusters/plant, pods/plant, seeds/pod, 100-seed wt. and yield/plant. The M2 populations showed
considerable increase in variance in all traits due to induction of micromutations. M2s of varieties
having higher expression of traits mostly showed negative skewness and reduction in mean due to
induction of more micromutations with negative effect on the trait. Conversely, M2s of varieties
having low values for traits showed positive skewness and increase in mean due induction of more
micromutations with positive effect. However M2s of varieties with moderate values did not show
skewness and were platykurtic (flatter) with out much change of mean from controls. This can be
attributed to almost equal frequent induction of micromutations with positive and negative effects.
Transgressive variation parameters indicated that selection for improvement of trait would be more
effective in M2s of RBL-50, BRB-4 and PRR-9302 for cluster/plant and pods/plant, of RBL-50 and
RBL-1 for seeds/pod, of BRB-4, RBL-1 and PRR-9302 for 100-seed wt. and of PRR-9302, RBL-50
and BRB-4 for yield.