English

Abstract

Heat stress is the most important abiotic factor affecting cotton crop. Exposure of cotton crop to different thermal regimes at different growth stages influences growth and seed cotton yield. The foliar spray of growth regulators at these stages improves yield and growth of cotton crop by mitigating the adverse effects of heat stress. Therefore, a field study was conducted to evaluate the potential role of different growth regulators on thermo-tolerance in cotton during two consecutive years (2012 and 2013). Different thermal regimes were provided at three reproductive stages by overwhelming different temperatures under field conditions (April 2, May 3 and June 17 during 2012 and April 4, May 2 and June 19 during 2013). Foliar spray of water spray (control), hydrogen peroxide (30 ppm), salicylic acid (50 ppm), Moringa leaf extract (30 times diluted) and ascorbic acid (70 ppm) were studied at squaring, flowering and boll formation stages. April sown crop produced highest seed cotton yield, plant height, more number of nodes for the first fruiting branch and monopodial branches followed by May and June thermal regimes. June sown crop showed higher unopened bolls than others. Hydrogen peroxide (H2O2) produced higher seed cotton yield per plant and monopodial branches in high temperature sowing dates (April and May) than optimal thermal regime (June sown crop). Moringa leaf extract (MLE) and ascorbic acid (ASA) also produced similar results under high temperature sowing dates. The H2O2 and SA reduced unopened bolls in all thermal regimes over the control while MLE and ASA showed similar results like water spray. All the growth regulators showed non-significant effect on node number for first fruiting branch in all thermal regimes except in April sown crop where H2O2 and SA reduced node numbers over the water spray.