Modification of Sex Expression and Floral Characteristics in Zucchini (Cucurbita pepo L.) through Foliar Application of Plant Growth Regulators

Abstract

Ethephon (2-chloroethylphosphonic acid) is one of the most widely utilised ethylene-releasing plant growth regulators in cucurbit production. When applied as a foliar spray at the two- to four-leaf stage, it decomposes within plant tissues to release Ethylene. This process suppresses the development of staminate (male) flowers while promoting the initiation of pistillate (female) flowers at lower nodal positions. A field experiment was conducted at the experimental field of the Department of Agriculture, Khalsa College, Amritsar, India, during the Rabi season of 2018–2019 (more precisely late Rabi–Zaid transition season) to evaluate the effect of foliar application of ethephon and maleic hydrazide at varying concentrations (50, 100, 150 and 200 mg L⁻¹) on sex expression, floral characteristics of zucchini (Cucurbita pepo L.) cv. Dark Green. The experiment was conducted in a Randomized Complete Block Design (RCBD) with nine treatments and three replications. Parameters assessed included sex ratio (male-to-female flower ratio), days to first flower opening, days to 50% flowering, number of fruits per plant. Results demonstrated that ethephon at 200 mg L⁻¹ (T4) produced the lowest male-to-female flower ratio (0.67), compared with 3.32 in the untreated control, indicating a pronounced shift in sex expression towards femaleness. T4 also recorded the minimum days to first flower opening (16.11 days) and to 50% flowering (20.15 days). Number of fruits per plant was significantly superior (4.09) under T4. Maleic hydrazide at lower concentrations (50–100 mg L⁻¹) showed moderate feminising effects on sex ratio, whilst higher concentrations (150–200 mg L⁻¹) had limited positive influence on yield. These findings suggest that ethephon at 200 mg L⁻¹ is the most effective treatment for modifying sex expression towards femaleness and improving fruit yield in zucchini under sub-tropical Punjab conditions.