The Effects of Temperature on Vegetative and Early Reproductive Growth of a Cold-Tolerant and, a Cold-Sensitive Line of Phaseolus vulgaris L. 1. Nodulation, Growth and Partitioning of Dry Matter, Carbon and Nitrogen

Nodulated plants of a cold-sensitive (Seafarer, SF) and tolerant (accession 194) line of Phaseolus vulgaris L. were grown under three temperature regimes, 15/10, 20/15 and 25/15 °C (light/dark). Dry matter, total C and N were measured in plant parts at three harvests. Both lines produced functional nodules at a mean growth temperature as low as 12-9 °C (15/10) but 194 produced more and larger nodules which fixed more N (total plant N) than SF. At the lowest temperature during early vegetative growth, 194 accumulated greater amounts of d. wt than SF but had similar RGR and NAR. RLGR and RGR expressed in terms of N on the other hand, were markedly greater in 194 than SF. 194 Partitioned more d. wt and N into shoots vs roots and had a lower leaf: stem d. wt ratio than SF. Both lines showed similar increases in leaf area, leaf area ratio and RGR with increasing temperature. The results suggest that the ability to nodulate well, increase nodule size in response to temperature stress and achieve maximum leaf expansion are important factors for the superior growth of 194 over SF. Key words: Phaseolus vulgaris, common bean, nodulation, growth, low temperature stress