Low Night Temperature Increases Ovary Size in Sweet Pepper Cultivars

Cool night temperatures have been reported to induce ovary swelling and consequent fruit deformation in bell pepper (Capsicum annuum L.), resulting in unmarketable fruit. This response is a serious limitation to the success of winter production systems for bell pepper. Limited work has been done with other types of sweet pepper, so it is unknown how universal this response is. Furthermore, most prior work has examined effects on ovary diameter only, and there is limited characterization of other ovary traits in response to cool night temperature. The objectives of the present study were to determine the effects of low night temperature on ovary characteristics in different sweet pepper cultivars and to determine the parts of the ovary that are most affected by these factors. Three types of sweet pepper (bell, long-fruited, and cherry) were exposed to 22/20 or 22/12 degrees C day: night temperatures and flowers at anthesis were continuously harvested throughout the experiments. Ovary fresh weight (FW), diameter, and length across all types (and cultivars within type) were greater under 22/12 degrees C compared with 22/20 degrees C. The increase in ovary FW was the result of increases in both ovary wall and placenta FW. In general, all cultivars exhibited increases in ovary size under 12 degrees C compared with 20 degrees C night temperature. Differences in ovary FW resulting from night temperature became more pronounced with time. These results indicate that low night temperature effects on ovary swelling may be a universal response among sweet pepper types. Three to 4 weeks are required for maximum swelling response, suggesting that flower buds must be exposed to low night temperatures within the first week after flower bud initiation, because previous work found that flower bud initiation in bell pepper takes 4 weeks. However, the duration of low night temperatures necessary for this response remains unknown.