Abstract
Effects of thermal conditions during seed ripening on bolting of Eustoma grandiflorum (Raf.) Shinn. seedlings grown at high temperatures were studied by preliminarily applying thermal treatments to immature capsules. A high temperature of 38/28°C (day/night) during ripening reduced the bolting rate compared to that under a cool temperature of 23/18°C. Bolting rates of seedlings subjected to 23/18°C treatment were almost equal to those of seedlings from ambient temperature in a rain-protection house from summer to autumn in a warm region of Japan. Immature ‘Aya-no-sakura’ capsules with peduncles were harvested three weeks after pollination, inserted into a preservative solution containing sugar, and incubated at temperatures of 10, 15, 20, and 25°C for three to eleven weeks. Three- to nine-week incubation at 10°C and three- to seven-week incubation at 15°C effectively increased the bolting rates of seedlings. Immature ‘Aya-no-sakura’ capsules gathered seven or nine weeks after pollination were held at 5.5, 9.5, 13.5, 17.5, or 21.5°C until dry. Seedlings dried at 5.5 to 17.5°C exhibited high bolting rates. These findings demonstrated that seeds could memorize thermal conditions applied during ripening and that chilling applied during seed ripening could promote bolting of seedlings. Cut immature capsules could respond to chilling, and consequently the seeds exhibited increased bolting rates, although cutting immature capsules from plants slightly reduced rosetting of seedlings.
