Too cold or too warm? Modelling seed set and fruit mass based on the effect of temperature on pollen quality.

Seed and fruit set are processes determining yield in many crops. However, many growth models for horticultural crops do not explicitly incorporate these processes. The aim of this study was to develop a quantitative model to predict seed set, fruit set, and fruit mass based on the effects of temperature and duration of a period with high or low temperature on pollen number and pollen quality (viability and germination fraction). To develop the model, we conducted an experiment where fruiting dwarf tomato plants were grown at 18°C and exposed to 14°C for 4, 6, or 8 days, 30°C and 34°C for 1, 3, or 4 days, and a control treatment at 18°C continuously. Temperatures of 30°C and 34°C reduced pollen viability and germination, resulting in lower seed set and fruit mass. While fruit set remained unaffected at 30°C, both 14°C and 34°C led to reduced fruit set. At lower temperatures (14°C), our model predicted decreased yields due to a lower number of fruits in the truss, resulting from reduced fruit set and smaller fruit size compared to the reference temperature (18°C). At higher temperatures (30°C), our model predicted reduced fruit yield due to smaller individual fruit size, resulting from low seed set. Our research introduces a modelling framework that accounts for the influence of periods with high or low temperature on seed set, a process that is almost never considered in growth models for horticultural crops. This framework is crucial for developing strategies to optimize crop yield in response to temperature fluctuations.