Symbiotic interactions of <i>Phaseolus acutifolius</i> and <i>P</i>. <i>acutifolius</i> × <i>P</i>. <i>vulgaris</i> hybrid progeny in symbiosis with <i>Bradyrhizobium</i> spp. And <i>Rhizobium leguminosarum</i> bv. <i>phaseoli</i>

Abstract

The rhizobial requirements and the N 2 -fixing potential of Phaseolus acutifolius and P. acutifolius × P. vulgaris hybrid progeny were investigated in glasshouse experiments. Although P. acutifolius was promiscuous, effective nodulation and N 2 fixation occurred only with a few Bradyrhizobium isolates, especially those that were isolated from P. acutifolius, P. limensis, P. penduratus, P. lunatus, Canavalia ensiformis, Calopogonium mucunoides, and Psophocarpus tetragonolobus. Strong host × Bradyrhizobium interactions were detected in four genotypes of P. acutifolius tested against eight isolates of bradyrhizobia and a commercial mixed inoculant. All seven progeny tested nodulated with Bradyrhizobium isolates and Rhizobium leguminosarum bv. phaseoli, but there was a highly specific rhizobial requirement for effective nodulation and N 2 fixation. The progeny × rhizobial interaction accounted for 83% of the total phenotypic variation. Two (P-6 and P-7) and five (P-1, P-2, P-3, P-4, and P-5) progeny nodulated and fixed N 2 effectively with R. l. bv. phaseoli and Bradyrhizobium spp., respectively. The R. l. bv. phaseoli – progeny symbiosis had a greater N 2 -fixing potential than the Bradyrhizobium isolate – progeny symbiosis. In a soil (oxisol) test, progeny P-6 and P-7 showed significant response to inoculation with R. l. bv. phaseoli. Strain R. l. bv. phaseoli TAL 182 was the most competitive strain, occupying 84% of the nodules in both the progeny. Key words: rhizobial requirements, Phaseolus acutifolius × Phaseolus vulgaris hybrids.