Gamma Radio Sensitivity Determination for Lablab (Lablab purpureus) Bean

Mutagens like gamma rays are known to influence plant growth and development by inducing genetic, biochemical, and morpho-genetic changes in cells and tissues. The selection of efficient and effective mutagens and mutagenic doses is important for the success of a mutation breeding programme. While high doses are known to produce very drastic effects in the cell leading to death of the organism, effective mutagenic doses vary even among closely related plant species. In this study, the radio-sensitivity of a Lablab purpureus selection from Kenya, DL002, was assessed by exposing the dry seeds to 150, 200, 250, 300 and 350 Gy of gamma rays. Dose sensitivity was determined by measurements of physiological and morphological parameters on the M1 generation and on the basis of frequency of various types of chlorophyll mutations obtained in the M2 generation. With the increase in radiation dose a decrease in germination, seedling height, leaf size, number of leaves, emergence and survival rate under field conditions was observed in the M1 generation. Chlorotic spots increased with increase in doses at the M1 generation but no stimulatory effect in any of the traits studied was recorded. Seedling height decreased with increase in gamma radiation dose in an approximately linear fashion. The lethal dose 50 (LD50) value for seedling height was 231 Gy. The effectiveness of the dose in inducing genetic changes was estimated by counting the number of chlorophyll and morphological mutations in the M2 generation. The frequency of mutations increased with the radiation dosage upto 250 Gy and then sharply decreased thereafter. The chlorophyll mutants observed included xantha and albina where the xantha type was more frequent than albino. The morphological mutants observed included early maturity, wrinkled leaves and seed coat colour. Based on the findings, it is proposed that the optimum dose for irradiating lablab bean using gamma rays is 200 to 250 Gy. (author)