Indian Journal of Plant Physiology

Plants of snap bean cultivar Haibushi (heat-tolerant) and Kentucky Wonder (heat-sensitive) were subjected to 24/20, 27/23 (normal), 30/26 and 33/29°C (day/night) temperatures after flowering (40 DAS). The number of leaves and leaf area per plant, dry matter accumulation and partitioning in different plant parts were measured. Dry matter partitioning contributed to differential heat tolerance of the two cultivars rather than leaf area and total biomass. The major differences between the two cultivars in 24/20 to 30/26°C were that dry matter accumulation and partition was higher to pods in heat-tolerant cv. Haibushi, while to the vegetative parts in heat-sensitive cv. Kentucky Wonder. The dry matter partition to vegetative parts displayed decreasing trend towards maturity in the former while no such trend was found in the latter indicating that the photo-assimilates from the vegetative parts were mobilized to pods in Haibushi while no such translocation occurred in Kentucky Wonder resulting in lower pods dry weight and harvest index. Dry matter partitioning was independent of temperature in heat-tolerant and temperature-dependent in heat-sensitive cultivar. Within temperature regimes, there was no difference in growth rates in Haibushi while in Kentucky Wonder the growth rates in pods dry weight and harvest index differed, significantly higher in 27/23 than 24/20°C. The differences in growth rates contributed to similar variations in pods dry weight and harvest index, which were temperature-dependent in Kentucky Wonder and independent of temperature in Haibushi. The better harvest index achieved in heat-tolerant cultivar was due to a greater mobilization of assimilates to pods as well as decrease in partitioning of dry matter to the vegetative parts towards maturity. Within temperature regimes from 24/20 to 30/26°C, Haibushi showed reduction in dry matter partitioning to leaves, stems and roots, while no such trend was found in Kentucky Wonder indicating wider temperature adaptability to elevated temperature in the former than the latter.