Influence of Plant Growth Regulators on Fruit Quality Attributes of Zucchini (Cucurbita pepo L.)

Abstract

Plant growth regulators (PGRs) are known to exert diverse and often dose-dependent effects on the biochemical composition and quality of cucurbit fruits. Ethephon, an ethylene-releasing compound, has been widely investigated for its capacity to modify sex expression, accelerate fruit development and alter the biochemical composition of fruits in cucurbitaceous crops. A field investigation was conducted at the experimental field of the Department of Agriculture, Khalsa College, Amritsar, during the Rabi season of 2018–2019 (more precisely 'late Rabi–Zaid transition season) to study the influence of ethephon and maleic hydrazide on the fruit quality attributes of zucchini (Cucurbita pepo L.) cv. Dark Green. The experiment comprised nine treatments — ethephon at 50, 100, 150 and 200 ppm; maleic hydrazide at 50, 100, 150 and 200 ppm; and an untreated control — laid out in a Randomized Complete Block Design (RCBD) with three replications. Both regulators were applied as foliar sprays at the two- and four-leaf stages. Three quality parameters were assessed: ascorbic acid content (mg per 100 g), total soluble solids (TSS, °Brix), and flesh thickness (mm). Ethephon at 200 ppm (T4) recorded the highest values for all three quality parameters — ascorbic acid of 16.93 mg per 100 g, TSS of 6.33 °Brix, and flesh thickness of 30.66 mm — whilst the untreated control (T9) recorded the minimum values of 11.90 mg per 100 g, 4.73 °Brix and 22.15 mm, respectively. Statistical analysis revealed that TSS was significantly influenced by the treatments (CD at 5% = 0.18), whilst ascorbic acid and flesh thickness showed consistent numerical trends though were not statistically significant. The enhancement of TSS under ethephon application was attributed to the influence of ethylene-related physiological processes on nutrient absorption and accumulation in fruit pulp. These findings indicate that foliar application of ethephon at 200 ppm at the two- and four-leaf stages represents an effective strategy for improving the biochemical quality of zucchini fruits under subtropical conditions.