Ethylene Control of Flowering and Sex Differentiation in Three Sex Types of Inbred Melon Lines

Flower types and sex expression are important traits for melon (Cucumis melo L.) and hybrid seed production. Here, we studied the effects of ethrel, aminoethoxyvinylglycine (AVG) and silver nitrate (AgNO3) on floral development and sex expression in andromonoecious, monoecious, and hermaphroditic inbred melon lines in an experimental field at Zhejiang University, Hangzhou China during the autumn of 2017. The application of 100, 200, and 400 mu L.L-1 of 40% ethrel delayed the initiation of male/bisexual flowers on the main stem and inhibited the formation of lateral branches bearing female/bisexual flowers. Ethrel exposure changed the flower sex type on the main stem of the three inbred melon lines. Melon sexual types could be converted from andromonoecious to hermaphroditic, from monoecious to gynoecious, and from hermaphroditic to gynomonoecious/gynoecious and be devoid of buds destined to be male flowers. The three inbred melon lines responded differently to ethrel during floral development and sex transition, with the monoecious line being the most sensitive and the hermaphroditic line being the most insensitive. The inhibitor of ethylene biosynthesis, AVG (100 mg.L-1), and the inhibitor of ethylene action, AgNO3 (300 mg.L-1), were ineffective in altering sex expression. However, the male/bisexual flowers on the main stem formed at lower nodes in AVG- or AgNO3-treated plants, resulting in earlier flower initiation for the hermaphroditic line. Thus, the application of AVG or AgNO3 promoted earlier fruit setting in hermaphroditic melon. In addition, the use of ethrel to induce male sterility in melon could replace the expensive labor necessary for the mechanical emasculation of hybrids and ensure hybrid seed purity.