Effects of common bean (Phaseolus vulgaris L.) cultivar and rhizobium strain on plant growth, seed yield and nitrogen content

The common bean is generally regarded as a relatively inefficient fixer of nitrogen. Information on the relative importance of host cultivar and rhizobium strain would be useful in guiding a breeding program to improve nitrogen fixation in common bean. Seventeen cultivars of common bean (15 of Meso-American and 2 of Andean origin, differing in nodulation potential, maturity, growth habit and market class) were investigated for symbiotic compatibility with 10 genetically diverse strains of bean rhizobia. In a greenhouse (27/22 °C), five sets of 170 pots were replicated over time: three sets were harvested after 30 d for determination of acetylene reduction activity, plant dry weights, and nitrogen content; two replications were grown to maturity for determination of seed dry weight and nitrogen content. There were highly significant effects of both strain and cultivar on most measured characteristics, but there was no interaction between cultivar and strain. Italian Barlotti produced the greatest plant weight after 30 d, but its final seed yield did not differ significantly from that of the highest yielding cv. BAT271. The strain TAL182 was associated with the greatest plant weight at 30 d, but the final seed yield associated with it was less than that of the most productive strain USDA9001. Strain USDA 2667 was characterized as type I by determination of its 16S rRNA gene nucleotide sequence. The nodules of plants in symbiosis with strains of type IIB had high levels (8.1%) of nitrogen and high levels (227 µmol g−1 h−1) of acetylene reduction activity (ARR). Nodules occupied by strains of type IIA and the type I USDA2667 had intermediate levels of nitrogen (6.9%) and ARR (166 µmol g−1 h−1), while nodules occupied by type 1 strains had low levels of nitrogen (5.2%) and ARR (144 µmol g−1 h−1). Screening of lines, parents and other breeding materials for improved N-fixation may be achieved with any effective strain since no host × strain interaction was detected. Key words: Common bean, Phaseolus vulgaris, nodulation, nitrogen fixation, rhizobium strains, cultivar × strain interaction