Enhancing heat tolerance in Bt cotton (Gossypium hirsutum L.) through different management practices

Abstract

High temperature stress is the problem in many parts of the world, especially under semi-arid regions of world affecting vegetative and reproductive stages of cotton crop. The experiments were conducted in field (2012 and 2013) of Department of Agronomy, University of Agriculture Faisalabad as well as in glasshouse (2012) of Department of Plant Breeding and Genetics, University of Agriculture Faisalabad, Pakistan to check the effects of foliar spray of growth regulators (hydrogen peroxide-H2O2, salicylic acid-SA, moringa leaf extract-MLE and ascorbic acid-ASA) and nutrients (potassium-K, zinc-Zn and boron-B) at three reproductive stages (squaring, flowering and boll formation) of cotton crop. Each reproductive stage under field conditions faced optimal, sub and supra-optimal temperatures while under glass house conditions optimal, sub and supra-optimal thermal regimes were provided (32/20°C ± 2°C, 38/24°C ± 2°C and 45/30°C ± 2°C). The effects of growth regulators and nutrients spray were seen for different antioxidants, ROS, MDA contents; gas exchange components; water relations, chlorophyll contents, membrane leakage, phenogical components, yield and quality attributes of cotton crop under all thermal regimes. Under both, field and glass house conditions, and for all reproductive stages (squaring, flowering and boll formation), hydrogen peroxide (H2O2 30 ppm) produced higher antioxidants, lower ROS and MDA contents under all thermal regimes followed by MLE and ASA. Hydrogen peroxide also induced higher water relation and gas exchange components; lower membrane leakage and higher chlorophyll contents under all thermal regimes while both MLE (30 times diluted) and ASA (70 ppm) showed comparable results only under high temperature regimes after H2O2 over the control (water spray). Salicylic acid (50 ppm) increased antioxidants only under high temperature regimes after MLE and ASA than the control. Both salicylic acid and hydrogen peroxide reduced different phenological components only under sowing dates that took higher days to accumulate the required growing degree days (GDD) while both reduced insect infected and unopened bolls than control and other regulators. Seed cotton yield, the related components and the quality attributes were increased by H2O2 while MLE and ASA stood at par with it only under high temperature sowing dates. Foliar spray of potassium (1.5%) or zinc (0.2%) stimulated higher antioxidants and lower ROS under all thermal regimes at all three reproductive stages in both field of studies followed by boron (0.1%) over the water spray (control). Foliar spray of either K or Zn showed higher water relations, lower membrane leakage, higher chlorophyll contents and gas exchange components only under high temperature regimes followed by B over the control. Both K and Zn induced earliness only in sowing dates which took more days for different phenological stages than B and control. Foliar spray of K or Zn showed higher yield related components and fiber quality attributes only under high temperature sowing dates. The results concluded that foliar spray of growth regulators (H2O2 followed by ASA and MLE) and nutrients (K and Zn) under heat stress conditions at any reproductive stage of cotton crop are helpful for mitigating the adverse effects and might have great importance under severe heat spells like those occurring in Pakistan.