Increased percentage of fruit set of F1 hybrid of Capsicum chinense during high-temperature period

Low percentage of fruit set in fruit vegetables cultivated in greenhouses, such as tomato (Solanum lycopersicum), eggplant (S. melongena), and capsicum (Capsicum), in high-temperature seasons has been reported as one of the biggest problems in commercial vegetable production. In this study, C. chinense 'Sy-2' and 'No. 3686' were cultivated in greenhouses for a year. Remarkably low percentages of fruit set (3.2% and 0%, respectively) were obtained in the high-temperature season (40 °C/25 °C: day/night). However, the percentage of fruit set was recovered with the decrease in temperature in autumn and winter (30 °C/20 °C). On the other hand, in F1 ('Sy-2' × 'No. 3686'), the percentage of fruit set was 40.8% even in the high-temperature season. On in vitro pollen germination test, the pollen of F1 was found to have a higher germination rate than that of 'Sy-2' or 'No. 3686' during the high-temperature season. After 'Sy-2' was cross-pollinated with 'Sy-2' and 'No. 3686' pollen, percentages of fruit set were 23.3% and 0%, respectively. It is noteworthy that the cross-pollination of 'Sy-2' with F1 pollen resulted in a considerably higher percentage of fruit set (73.3%). When F1 was self-pollinated, the percentage of fruit set (56.7%) was higher than that after when cross-pollinated with 'Sy-2' or 'No. 3686' pollen. Interestingly, no fruit set was obtained when 'No. 3686' was cross-pollinated with 'Sy-2', 'No. 3686', or F1 pollen. The results for 'No. 3686' indicated that not only does the male factor affect pollen germination ability but also unknown female factors are involved in reducing the percentage of fruit set of C. chinense under the high-temperature season. A significant increase in the percentage of fruit set in the high-temperature season was also observed in the reciprocal cross of F1, 'No. 3686' × 'Sy-2'. Furthermore, 10 plants of ('No. 3686' × 'Sy-2') × 'Sy-2' and 31 plants of 'Sy-2' × ('No. 3686' × 'Sy-2') were cultivated in a greenhouse, but no difference was found in the percentage of fruit set between these two combinations. Therefore, our findings suggest that cytoplasmic factor(s) does not influence the percentage of fruit set.