Dry Matter Production and Fruit Sink Strength Affect Fruit Set Ratio of Greenhouse Sweet Pepper

We investigated the relationships among the fruit set, dry matter production, and source-to-sink ratio of sweet pepper (Capsicum annuum) plants grown in a greenhouse. We quantified daily fruit sink strength per stem (st) at m days after transplanting (SSTm_st) by modeling the fruit growth curve. The daily total dry matter production (TDMm_st) was calculated and defined as the source strength. During an experiment lasting ≈250 days, the fruit set ratio [number of fruit harvested/number of flowers (FSRm)] decreased significantly with increases in both the weekly average SSTm_st from 9 days before anthesis (DBA) to 13 days after anthesis (DAA) and the weekly average fruit number (FRNm_st) from 9 to 1 DBA. FSRm increased significantly with increases in both the weekly average TDMm_st from 1 to 13 DAA and the weekly average source-to-sink ratio [source strength/fruit sink strength (SSRm_st)] from 5 DBA to 13 DAA. During the whole experimental period, significant positive correlations with FSRm were observed for TDMm_st and SSRm_st, and significant negative correlations with FSRm were observed for SSTm_st and FRNm_st. FSRm increased until approximately the time when the weekly average SSRm_st at 1 to 7 DAA (anthesis to 156°C⋅d−1) ranged from 1.0 to 4.0; then, it showed a saturation curve at SSRm_st values more than 4.0 (R2 = 0.81). These results suggest that it is possible to moderate the fluctuations in sweet pepper yield by monitoring the SSRm_st and the number of fruit set.