Efficiency and effectiveness of physical and chemical mutagens and their combination in inducing chlorophyll mutations in M₂ generation of Lablab [Lablab purpureus (l.) Sweet var. Typicus]

A comparative study of the frequency and spectrum of chlorophyll mutations induced by gamma rays (150, 200, 250, 300 and 350 Gy), sodium azide (0.5, 1.0, 1.5 and 2.0 mM) and combination treatments of gamma rays and sodium azide (100 Gy + 1.5 mM, 150 Gy + 1.5 mM, 200 Gy + 1.0 mM, 250 Gy + 1.0 mM and 300 Gy + 0.5 mM) in M₂ generation A was made in the lablab var. CO 9. Four different types of chlorophyll mutants viz., albina, viridis, chlorina and xantha were identified in the treated population and mutation frequency was calculated on plant population basis. Frequency of chlorina mutants was highest followed by albina, xantha and viridis. Combination treatments in general proved to be very effective followed by sodium azide and gamma rays in inducing maximum frequency of chlorophyll mutations. Although the chlorophyll mutations do not have any economic value due to their lethal nature, such a study could be useful in identifying the threshold dose of a mutagen that would increase the genetic variability and number of economically useful mutants in the segregating generations.