Consumers seek locally grown tomatoes for their superior flavor, making them a valuable crop for local vegetable growers. Tomato production can be difficult with the temperature requirements for fruit set, development, and ripening. Optimum growing conditions are available for a short period in Oklahoma, causing a distinct decline in production during late July and August. A field experiment was designed to investigate the success of late planted, heat tolerant tomatoes in Oklahoma field conditions, as well as explore the relationship between physiological responses and season-long temperatures. The experiment utilized a split plot design with three transplanting dates as whole plot and five cultivars as subplot. ‘Red Snapper’ and ‘Laguna Red’ were selected as potential heat sensitive cultivars. ‘Bella Rosa’, ‘Volante’, and ‘Florida 91’ were selected as heat tolerant cultivars, based on previous trial information. Planting occurred on April 23, May 9, and May 23 to represent early, mid, and late plantings dates, respectively. Physiological measurements were collected every two weeks and included electrolyte leakage, net photosynthetic rate, stomatal conductance, leaf temperature, and chlorophyll fluorescence. Plants were harvested routinely from June to the end of August. Cultivars were not found to be significantly different in the trial for yield or physiological responses. The early planting date was the most productive, compared to mid and late. Yield dropped dramatically for all planting dates in August. There was a strong positive correlation between electrolyte leakage and temperature and a moderate negative correlation between photosynthetic rate and average daily temperature. These correlations indicate that physiological parameters may be able to provide insight into late season thermotolerance. Future research will involve cultivar screenings in controlled environments to promote a wider range of responses to temperature.
