Use of .gamma irradiation to inuuce varlability in desirable agronomic characteristic common bean (Phaseolus vulgaris L (var. GLP-2).

Abstract

The common bean (Phaseolus vulgaris L) is the leading pulse crop in Kenya but the yields are low as a result of several biotic and abiotic constraints. Wortman and Allen (1994) indicated that angular leaf spot, anthracnose, bean stem maggot, bruchids, low soil nitrogen and low soil phosphorus are the most important constraints to greater productivity. c, Infestation by bean bruchids (Acanthoscelides obtectus Say)" during storage is one of the major biotic constraints leading to heavy losses in quality and quantity. Control measures currently used by the. farmers are ineffective o~·too expensive and beyond the reach of the majority of farmers. Breeders have been unable to select for desirable traits due to limitation by variability. This study was designed to induce variability to desirable characters in common bean through mutation breeding .. Seeds of a commercial bean variety (GLP 2) were soaked in distilled water for 4 hours and irradiated by exposure to gamma rays from a T780 cobolt-GO unit. Three doses of gamma . " c, irradiation (150. 200 and 250 Gy) and a control were used. It was designed that 1200 seeds be irradiated in 3 lots of 400 seeds per dose but subsequent problem with the equipment during .irradiation reduced this to 1113 seeds. Irradiated and 'control (the same GLP-2 but . . not irradiated) seeds were grown in the field and the types and frequencies of easily identifiable morphological mutants recorded in the generations I, 2 and 3 (M I. M2 and M3) populations during crop growth. In addition. the M3 lines were evaluated for agronomic performance and. resistance to bruchids. In the M I and M2 generations, reduction in germination % was the most notable effect for all the irradiated materials. One . . . (~ . partially yellow mutant plant was identified in the M2 population irradiated with 150 Gy. "~ Gy. In the M3 generation, there were major differences among mutant lines, both within and between the lines. A spectrum of mutations that included variants in chlorophyll pigmentation, flower colour, growth hab. it, seed . colour, maturity date, ancl yield and yield components were observed. Lilies with significant increases in desirable characteristics such as early maturity, seeds per pod, and yield were identified. These lines are available for further evaluation in M4 and later generations. Induction of resistance to bean bruchids was IIOt rcalised. It WIIS suggested that more dosage levels be tried in future work.