Improving thermotolerance in Gossypium hirsutum by using signalling and non-signalling molecules under glass house and field conditions

Abstract

The climate change and global warming driven rise in temperature and unpredictable occurrence of heat waves impede cotton plants growth and development. Therefore, environmental friendly thermotolerance strategies are required to sustain optimum crop yield under stressful conditions. Reports on heat stress impacts on plant water relations, gas exchange attributes and physiological parameters, at different reproductive stages of cotton, under controlled and natural conditions are lacking. To investigate the impact of temperature and exogenous application of elicitors, a medium heat tolerant cotton genotype was exposed to control/optimal (30/20 °C), medium (38/24 °C) and high (45/30 °C) temperature stress at squaring, flowering and boll formation stages. Plants were staggered to April (early), May (normal) and June (late) sowing dates under field conditions. Growth regulators, salicylic acid (SA-50 ppm), bio-stimulant moringa leaf extract (MLE-30 times diluted) and signaling molecules, i.e. hydrogen peroxide (H2O2 -30 ppm) and ascorbic acid (ASA-70 ppm), were applied foliarly one day prior to temperature stress treatments. Several physio-biochemical parameters, such as leaf non-enzymatic antioxidant, gas exchange attributes and water relations were measured seven-days after exposure to medium and high temperature regimes. Elevated temperature (45/30 °C) increased the content of total soluble proteins (TSP), activity of glutathione reductase (GR), radical scavenging capacity (DPPH%) and H2O2 generation by 64 %, 26 %, 39 % and 57 %, respectively, compared with optimal temperature plants (control). Similarly, the stomatal conductance (GS), seed index and ginning out turn (GOT%) were reduced by 49 %, 47 % and 44 %, respectively under the high temperature regime compared with control temperature regime. Gas exchange components, water relations, seed index and GOT were also reduced under medium and high temperature regimes. Among the exogenous applications, H2O2 showed profound alleviation of temperature stress, followed by ASA and MLE. Foliar application of H2O2 increased TSP, GR and DPPH% by 1.16 folds, 70 % and 82 % (averaged across during three reproductive stages); while, GS, seed index and GOT were increased by 45 %, 20 %, 22 % under high temperature stress over the control plants of the same thermal regime. In conclusion, oxidative burst and antioxidant activities were increased, whereas stomatal conductance, seed index and GOT were reduced with increasing temperature from 30/20 °C to 38/24 °C and from 38/24 °C to 45/30 °C. On the other hand, H2O2 improved thermotolerance of cotton plants via maintaining cellular redox balance, gas exchange attributes, and further enhanced seed weight and ginning out turn under medium and high temperature regimes.