Key Factor and Period Affecting Sweet Pepper Fruit Size: Air Temperature during Anthesis

The fruit size of sweet pepper ( Capsicum annuum ) fluctuates during production. Fruit size may be influenced by air temperature during anthesis and by competition for assimilates between vegetative and reproductive organs during fruit growth; however, its precise effects remain unclear. This study aimed to determine the key factors affecting fruit size of sweet pepper cv. Artega plants that grown in a greenhouse. Fruits were grown with and without fruit load under optimal to high air temperature; then, the effect of air temperature during anthesis on fruit fresh weight (i.e., fruit size) was analyzed. Daily assimilate competition was estimated by dividing the daily produced total dry matter by the daily increase in fruit dry weight. The results showed that the daily average air temperature for 1 to 7 days after anthesis was negatively correlated with fruit fresh weight within the temperature range 18 to 30 °C and that even fruits grown without fruit load showed low fresh weight at high air temperatures during anthesis. Significant flower abortion characterized at sweet pepper reduced fruit dry weight accumulation without affecting total dry matter produce. This abortion weakened assimilate competition, implying that fruits could have sufficient dry matter for their growth. Therefore, assimilate competition during fruit growth may have affected fruit size to a lesser extent than air temperature for 1 to 7 days after anthesis. In conclusion, the key factor affecting sweet pepper fruit size is air temperature during anthesis; high air temperature during this period leads to small fruit size.