Seeds from two varielies of common bean (Phaseo/us vulgaris) were irradiated
with four doses of gamma rays to induce mutations affecting Rhizobium symbiosis. as
the development of N2"fixing nodules requires a coordinated expression of genes of
both symbiotic partners. Symbiotic response to irradiation affecting leguminous host
was measured in two generations using wild type strain oi rhizobia. Both doses of 20
and 40 Krad revealed higher symbiotic efficiency in M. and M~ populations.
respectively. Inoculation with rhizobia was shown to decrease the deleterious effect of
radiation below that of un inoculated ones. Gamma irradiation disrupted the normal
ontogeny leading to reduction the development of new tissues in some vegetative
traits. leaf area was markedly reduced by gamma irradiation, and was suitable for
radiosensitivity assay depending on the growth of genotypes. Leaf area was
significantly affected by both doses of gamma irradiation and biofertilization among M,
and ~ populations. Protein content and chlorophyll concentrations in most of \he
inoculated plants was higher than uninoculated ones. Plants inoculated with rhizobia
produced higher seed protein content than uninoculated ones. The interaC\!on
between varieties by biofertilization significantly affected shoot nitrogen content
among M, and M2 populations. Pod productivity in both generations was markedly
affected by ptant genotypes, doses of gamma rays and biofertilization. Reductions in
seed and pod yields I plant were observed in M, and M2 populations as dosages of
gamma rays progressed. The results indicated that plant is most sensitive to gamma
irradiation from the time it begins to develop its reproductive capability until after
fertilizaUon when embryo development begins. Irradiation was used in this study to
induce genetic variatioo in common bean to enhance the response of rhizobia and
the legume host to increase N, fixation.