Frequency and spectrum of chlorophyll mutations and induced variability in ricebean (Vigna umbellata Thunb, Ohwi and Ohashi)

A comparative study of frequency and spectrum of chlorophyll mutations induced by physical (gamma rays) and chemical mutagens (EMS) in relation to the effect of mutations in M₁ plant, induction of mutants in M₂ and variability studies in M₃ generation was made in two ricebean (Vigna umbellata Thunb, Ohwi and Ohashi) varieties; one local (Totru Local) and one widely cultivated one (BRS-1) during 2005–2008. The treatments included three doses each of gamma rays (30, 40 and 50 kR) and EMS (0.50, 0.60 and 0.70%). Both gamma rays and EMS proved to be hazardous for germination and plant survival at higher dose and the comparative reduction in these characters was higher under EMS treatments than gamma rays. The frequencies and spectrum of five different kind of induced chlorophyll mutations was in the order; viridis > xantha = albina > chlorina > albo-viridis in BRS-1 and viridis > xantha > albina > chlorina = albo-viridis in Totru Local. EMS was found to be more effective in inducing maximum frequencies of chlorophyll mutants than gamma rays. Highest frequency of chlorophyll mutants were found under O.50% EMS in BRS-1 and 0.70% EMS in Totru Local. Genotypic differences were seen as highest frequency of mutations was observed in Totru Local which was more sensitive to mutagenic treatments than BRS-1. The coefficients of variation for all quantitative characters studied in M₃ generation were of higher magnitude compared to control in both the cultivars. The lower doses (30kR in gamma rays and 0.50% in EMS) were found to be the most important doses for inducing desirable variability in ricebean and three traits i.e. pods per cluster, seeds per pod and pod length showed high heritability coupled with high genetic advance in both BRS-1 and Totru Local indicating that breeding for these traits can be achieved by phenotypic selection.