Control of Sex Expression in Cucumber by Photoperiod, Defoliation, and Plant Growth Regulators

Abstract

Influences of photoperiod, defoliation, and growth regulators (AgNO₃, ethephon, gibberellic acid, and uniconzole) on sex expression were observed in three cultivars of cucumber, Cucumis sativus L. Eight photoperiod (SD) condition increased number of pistillate flowers and decreased number of staminate flowers in a monoecious cucumber, ‘Sagami-hanjiro’ Defoliation increased number of staminate flowers under SD. Ethephon decreased number of staminate flowers under SD, but had no effect under 24 h light photoperiod (LD) in defoliated plant. Gibberellic acid (GA) increased number of staminate flowers regardless of photoperiod and defoliation. LD slightly increased number of staminate flowers in a monoecious ‘Otone No.1’. Defoliation significantly decreased number of pistillate flowers under LD. Ethephon decreased number of staminate flowers and increased pistillate flowers under both photoperiodic conditions. The effect of ethephon was nullified by defoliation. Uniconazole markedly decreased number of staminate flowers and increased pistillate flowers regardless of photoperiod and defoliation. Uniconazole also induced bisexual flowers. Agynoecious cucumber, ‘Rensei’ produced almost only pistillate flowers under both SD and LD, and this tendency was not affected by defoliation. AgNO₃ induced staminate flowers and decreased number of pistillate flowers under LD and also under SD if defoliated. GA₃ decreased number of pistillate flowers in all treatments by causing blind nodes where neither floral nor vegetative buds developed.