| dc.description.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
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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. | en |
