Exogenous application of 4-chlorophenoxyacetic acid on morphological and yield traits of tomato (Solanum lycopersicum L.) during summer cultivation

Abstract

Tomato (Solanum lycopersicum L.) is one of the most economically important vegetable crops in Pakistan. However, its productivity is severely limited during the summer season due to high temperature and humidity, which adversely affects reproductive processes such as pollination, fruit setting, and flower retention. This study was conducted to evaluate the effect of exogenous application of 4-chlorophenoxyacetic acid (4-CPA), a synthetic auxin, on the growth and reproductive traits of two tomato cultivars, Roma and VCT-1, under summer climatic conditions in Islamabad. A field experiment was laid out in a Randomized Complete Block Design (RCBD) with three replications, using foliar sprays of 4-CPA at concentrations of 0 (control), 15, 30, and 75 ppm. Using a Randomized Complete Block Design (RCBD), four doses of 4-CPA (0, 15, 30, and 75 ppm) were sprayed on leaves at the research farm, National Agricultural Research Centre (NARC), Islamabad. Results revealed that 4-CPA application significantly enhanced plant height (59 %), leaf number (52 %) and fruit set (3.75 times) with the 75 ppm concentration showing the most promising effects on Roma and VCT-1. However, high humidity and temperature fluctuations remained major constraints, impacting anther dehiscence, stigma receptivity, and pollination efficiency. These findings suggest that 4-CPA can mitigate the adverse effects of summer stress by promoting vegetative growth, accelerating reproductive development, and enhancing fruit set. The 75-ppm concentration was the most effective across both cultivars. However, optimization of application timing and concentration, along with integrated stress and pest management, is recommended for sustainable improvement in tomato productivity under heat-stressed conditions. © 2025 The Author(s)