Effects of Photoperiod on Flower Bud Initiation of Some Okra (Abelmoschus esculentus) Cultivars in Spring and Autumn

Abstract

Effects of photoperiod on flower bud initiation of eight okra (Abelmoschus esculentus) cultivars were investigated in spring and autumn. The plants received 10 hr of natural day-length in short-day (SD) or natural day-lengths (ND) ranging from 14.16 to 14.29 in the spring and 11.07 to 12.17 in the autumn. To adjust for a 16-hr photoperiod (LD), the ND was extended with fluorescent lights (3μmol·m-2·s-1). Flower buds of 'Clemson Spineless' and 'Emerald' were initiated at the lower node, and they occurred earlier under SD than did those under LD or ND in the spring. Promotive effects of the short-day response in 'Clemson Spineless' and 'Emerald' were not clear in autumn; photoperiodic responses of both cultivars may have been modified by low air temperatures. On the other hand, flower buds of 'Benny', 'Gulliver', 'Natsu no Megumi', 'Star Debut', 'Star Light' and 'Suisei Gokaku' which were initiated at the similar node, occurred simultaneously, regardless of day-length and season. Flower bud initiation of all cultivars continued under short-day in spring and all day-length treatments in autumn. In contrast, a reversion to the vegetative phase occurred not only in 'Clemson Spineless' and 'Emerald' but also in 'Benny', 'Star Debut' and 'Suisei Gokaku' under LD and ND in the spring. Based on these results, 'Clemson Spineless', 'Emerald', 'Benny', 'Star Debut' and 'Suisei Gokaku' are believed to be quantitative short-day plants for flower bud initiation, whereas 'Gulliver', 'Natsu no Megumi' and 'Star Light' are day-neutral.