Photosynthesis, Dark Respiration and Bud Sugar Concentrations in Pepper Cultivars Differing in Susceptibility to Stress-induced Bud Abscission

Abstract

Pepper (Capsicum annuum L.) cultivars differ in susceptibility to stress-induced abscission. Previous research indicates that the stress susceptible cultivar 'Shamrock' undergoes a larger reduction in net assimilation rate (NAR) under low light stress, and partitions less dry matter (DM) to reproductive structures and more to leaves than the more tolerant cultivar 'Ace'. To determine if photosynthetic rates under low light stress could explain NAR differences, photosynthesis was measured on 'Ace' and 'Shamrock'. Assimilate partitioning was compared through measurement of leaf and bud respiration rates and analysis of bud sugar concentrations. Photosynthetic rates per unit leaf area of leaves fully exposed to incident light revealed no cultivar differences under low light conditions. Bud respiration rates fell to a lower level in 'Shamrock' than 'Ace' in low light-stressed plants, while expanded leaves respired at higher rates in 'Shamrock' than 'Ace' under both full and low light. Bud sugar concentrations were significantly lower in 'Shamrock' than 'Ace' after 3 d of low light stress. Susceptibility to low light stress-induced abscission in 'Shamrock' appears to be associated with reduced assimilate partitioning to flower buds, which may be related to high assimilate consumption in maintenance of expanded leaves.