Climate change is a source of severe stress for crops and reduces agricultural yields worldwide, with the Mediterranean region experiencing some of the most intense impacts. With a growing global population, agriculture faces the dual challenge of mitigatinge the adverse effects of climate change while meeting increasing food demands. One important challenge in eggplant (Solanum melongena) cultivation is the disruption of the plant's reproductive development under high temperatures. Eggplant exhibits andromonoecy, a sexual system where hermaphrodite and male flowers coexist on the same plant. Specifically, eggplant displays functional andromonoecy, where male flowers retain a non-functional pistil. Different eggplant varieties display different proportions of hermaphrodite and male flowers, but it has been shown that the proportion of male flowers always increases under heat stress conditions—a response aimed at conserving plant resources but resulting in yield reduction for farmers. It has been suggested that the balance between male and hermaphrodite flowers is linked to stress and resource allocation. Therefore, under stressful conditions, eggplants are thought to produce more male flowers, because they require fewer resources and avoid the metabolic cost of fruit development. Nevertheless, this hypothesis has not been systematically tested so far.
In this study, we investigated the impact of heat stress on the production of hermaphrodite and male flowers in the experimental eggplant variety “Micromel”, developed in our laboratory, and commercial varieties from Valencia, Spain, that were grown in the field. Furthermore, we assessed whether biostimulants derived from plant organic matter and enriched with aminoacids, applied during the vegetative phase, could improve plant resilience, thus maintaining fruit set under heat stress conditions
This study also explored the above hypothesis by testing the effect of the application of a biostimulant on flower sex and fruit set. For this, we used the dwarf eggplant variety (“Micromel”), developed in our laboratory. Micromel plants treated with the biostimulant during the vegetative phase produced significantly more hermaphrodite flowers and higher fruit yields than control plants, supporting the idea that the andromonoecy strength is controlled by resource availability.
To assess the impact of heat stress on andromonoecy, a subset of plants were exposed to heat stress (35ºC day/30ºC night). While the control plants under heat stress ceased producing hermaphrodite flowers, the biostimulant-treated plants continued to produce them. Although the fruit set was limited in the biostimulant-treated plants due to reduced pollen viability at high temperatures, these plants showed greater resilience to stress, suggesting a faster recovery post-stress. Additionally, when subjected to secondary stresses like drought, the biostimulant-treated plants exhibited enhanced tolerance.
Overall, these results support the idea that the strength of andromonoecy is linked to resource allocation in eggplant and that biostimulant application may support eggplant yield by promoting flower fertility and fruit set and improving stress tolerance. This approach offers a promising strategy for crop management in the face of climate change.
