Inhibitory effects of (S)-(+)-abscisic acid on bolting in Japanese radish [Raphanus sativus]

Three experiments were conducted on the effect of abscisic acid (S-ABA, the natural form) on bolting of Japanese radish (Raphanus sativus L.). Exp. 1. Dry or pre-imbibed seeds of Japanese radish (cv. Taibyousoubutori) were soaked in water (control), 100 or 1, 000 ppm S-ABA for 24 or 48 hr at 15 °C and sown immediately into small planter (6 x 6 x 6 cm3) filled with soil. The planters were kept at 8 °C for 10 or 20 days and then transferred to a growth chamber kept at 22 °C (day) and 18 °C (night). Treatment with 1, 000 ppm S-ABA significantly inhibited bolting of the seedlings. Exp. 2. Four lots of seeds was soaked in water, 250, 500 or 1, 000 ppm S-ABA at 15°C for 24 hr, allowed to dry completely, stored at 4 °C for 5 months and then sown in planters as above. The inhibitory effect of S-ABA on bolting of seedling persisted throughout the drying and storage periods. Exp. 3. Pre-germinated seeds of eight Japanese radish cultivars were dipped in water or 50 ppm S-ABA at 5 °C for 20 days and then sown. In another test, young seedlings of eight radish cultivars were sprayed with water or 250 ppm S-ABA during vernalization for 14 days at 8 °C. Thereafter, they were grown in the greenhouse. Seed-dipping or foliar spray applications of S-ABA inhibited bolting. The efficiency of S-ABA, however, was cultivar-dependent ; seeds and seedlings of 'Taibyousoubutori' and 'Natsuminowase No. 3' were most sensitive to S-ABA, whereas those of "Wakayama" and 'Kaiwaredaikon' were less sensitive. The treatment with 50 ppm S-ABA on pre-germinated seeds was more inhibitory than was the foliar application at 250 ppm. These results show that S-ABA is useful in preventing bolting of Japanese radish.