| In bell peppers (Capsicum annuum L.), low night temperature and high source:sink ratios during the preanthesis stage cause swollen ovaries, i.e., abnormally enlarged ovaries, resulting in low quality fruits. The physiological reasons for this ovary response are still unclear, but excess carbohydrate accumulation in ovaries has been implicated. In this research, it was found that low night temperature (LNT, 12°C) induced ovary swelling in three types of sweet peppers (cherry, elongated, and blocky bell), with the greatest response occurring in bell peppers. Three to four weeks of continuous LNT were required for maximum response, which coincides with the timing required for flower bud initiation in pepper. This suggests that flowers must be exposed to LNT soon after initiation in order for this response to occur. A second set of experiments showed that both LNT and fruit removal (i.e. increasing the source:sink ratio) increased the incidence of swollen ovaries in sweet pepper. Fruiting plants under LNT and non-fruiting plants under optimum night temperature (20°C) produced an intermediate-sized ovary, suggesting that night temperature of 20°C combined with high source:sink ratio or night temperature of 12°C combined with low source:sink ratio can partially overcome the detrimental effects of low night temperature or high source:sink ratio on ovary swelling in pepper. Both LNT and fruit removal decreased net carbon exchange rate without affecting total plant dry weight. This suggests that excess availability of current photosynthate (via maintaining similar carbon exchange rates and reducing plant growth) is not the mechanism that results in the increase in swollen ovaries observed under both LNT and high source:sink conditions. Ovary carbohydrate analysis and anatomical analysis revealed marked differences between swollen ovaries produced under LNT vs swollen ovaries produced under high source:sink ratios. Low night temperature increased floral ovary reducing sugar and starch concentration, while high source:sink ratios had no effect on ovary carbohydrate concentrations. Ovaries developed under LNT had thicker ovary walls and greater transverse area, with only slight increases in cell size and number. In contrast, ovaries developed under high source:sink ratios increased floral ovary size mainly through increased cell size. Finally, both LNT and high source:sink ratio increased ovary size through mechanisms that appear to be different. |
