Effects of heat stress on flowering, fruit set, and seed quality in pepper (Capsicum annuum L.)

Abstract

This study investigated the impact of heat stress on reproductive development in two pepper varieties, Cayenne and Yolo Wonder, by comparing two planting dates (March 20^th and May 1^st) in Iraq. The experimental design was a Randomized Complete Block Design in a 2×2 factorial arrangements. The later planting date exposed plants to severe heat stress, which significantly impaired all measured reproductive parameters. A dramatic increase in flower abscission was observed, particularly in Yolo Wonder (67.85%), along with a severe reduction in fruit set percentage (54.9% for Cayenne vs. 20.8% for Yolo Wonder). Heat stress also negatively affected fruit morphology, reducing average fruit weight to 51.8g for Cayenne and 74.8g for Yolo Wonder. Seed quality was considerably compromised, as an evident reduction in the number of seeds per fruit (95.0 for Cayenne vs. 62.4 for Yolo Wonder) and final germination percentage (88.36% for Cayenne vs. 65.05% for Yolo Wonder). Statistical analysis confirmed significant main effects of variety and planting date, as well as a significant interaction for most traits, underscoring the differential response of the two varieties. The Cayenne variety consistently exhibited superior thermotolerance across all parameters, highlighting its greater genetic resilience compared to the highly sensitive Yolo Wonder. Therefore, it is recommended to cultivate the heat-sensitive Yolo Wonder variety only during spring or autumn to avoid summer heat. In contrast, the heat-tolerant Cayenne variety can be successfully cultivated during summer months, maintaining acceptable productivity under heat stress conditions. These findings emphasize the critical importance of variety selection and planting schedule optimization for sustainable pepper production in heat-prone regions like Iraq.