Temperature constraints on tomato production challenge local production in warm climates. In Oklahoma, there is a narrow optimum temperature window required for fruit set, which ultimately results in a decline during late July and August. Growers are motivated to select heat tolerant tomato genotypes for better results. Previous research shows that there is a range of physiological responses when considering heat tolerant and heat sensitive cultivars. To investigate further, a controlled environment trial will be designed to evaluate eight different tomato cultivars at two different temperature regimes, optimum (26°C / 20°C) and elevated (36°C/26°C). Morphological measurements will be collected daily and are to include days to first truss, days to first open flower, days to first fruit set, and flower-fruit set ratio. Non-destructive physiological measurements will be collected weekly, including net photosynthetic rate, stomatal conductance, leaf temperature, and chlorophyll fluorescence. Electrolyte leakage will be measured once upon the completion of the trial. Differences in net photosynthetic rate and stomatal conductance were found to be significant between the two temperature regimes (p > 0.001) at 28 days after transplanting. Net photosynthetic rate averages were 4.358 µmol m-2 s-1 for the elevated temperature and 7.815 µmol m-2 s-1 for the optimum temperature. Stomatal conductance averages were 0.081 mol m-2 s-1and 0.150 mol m-2 s-1 for elevated and optimum regimes respectively. A Euclidean Distance will be calculated between the responses to the two temperatures upon completion, creating a heat tolerant index. The results will assist with the development of a screening tool for heat tolerant cultivars.
