Influence of temperature on growth and nitrogen fixation in cultivars of Phaseolus vulgaris L., inoculated with Rhizobium
SUMMARYGrowth and nitrogen fixation of three cultivars of Phaseolus vulgaris L., inoculated with strain CIAT 161 of R. phaseoli, were compared at day-night temperatures of 36–25, 30–20 and 26–15 °C.Temperature affected the duration and magnitude of N2 (C2H2) fixation. Maximum fixation increased from 33·8 μmol C2H4 produced/plant/h at 35–25 °C to 73·0 μmol C2H4 produced/plant/h at 25–15 °C, but the peak in fixation was increasingly delayed as growth temperature was reduced. In the 25–15 °C treatment this delay in the onset of fixation led to decreasing leaf nitrogen concentrations and visible N-deficiency symptoms at the 28 day harvest.Varietal differences in response to temperature were not marked, though one cultivar achieved greater nodule development at 35–25 °C than the others. This earlyflowering cultivar again appeared weak in N2 (C2H2) fixation with low specific nodule activity at all temperatures studied.Results are related to bean production in Latin America, and to the possible need for ‘starter’ nitrogen in the cooler bean-producing regions.