Abstract

The objectives of the present investigation was to study: (i) the symbiotic nitrogen fixation by Rhizobium etliand Rhizobium tropici in non-senescing nodules of ten common bean cultivars growing in greenhouse, and (ii) determination at least one plant characteristic which could be used as a reliable estimator of grain yield during the early stages of the crop. Ten economically important common bean cultivars were inoculated with R. etlistrain CE-3 or with R. tropici strain CIAT899 and grown in greenhouse conditions during three months. The results showed that nitrogen fixation was significantly higher when common bean was inoculated with R. tropici strain CIAT899, while acetylene reduction assay, total nodules and nodule fresh weight shows a significant positive correlation (P≤0.0001) with the yield during four weeks after the inoculation but not thereafter. Additionally, yield per plant was significantly and positively correlated with dry weight stem, dry weight root and dry weight leaf (0.80, 0.80, and 0.81, respectively; P≤0.0001). This suggests that acetylene reduction assay, total nodules and nodule fresh weight are a reliable estimator of yield during the early stages. It could be a helpful tool in programs of plant breeding when a fast land plant test, that is, number of nodules or fresh weight of nodules are a reliable estimator of grain yield during the early stages.

Key words: Early stages, nitrogen fixation, nodulation, Phaseolus vulgaris L, plant breeding, reliable estimator of yield.