INTEGRATION OF PHYSIO-BIOCHEMICAL PROCESSES AT DIFFERENT PHENOLOGICAL STAGES OF WHEAT (TRITICUM AESTIVUM L.) PLANTS IN RESPONSE TO HEAT STRESS

A study was conducted to assess the influence of heat stress imposed at different growth stages of wheat (Triticum aestivum L.) plants. Four wheat cultivars namely S-24, Saher-2006, Lasani and AARI-10 were subjected to high temperature (HT) stress at tillering and booting phenological phases. Under stress conditions, root and shoot fresh weights, membrane thermostability (MTS) and non-photochemical quenching (NPQ) were significantly perturbed in all four wheat cultivars at both developmental stages. However, HT stress did not influence all the other attributes significantly including shoot fresh weight, chlorophyll a and b pigments, photosynthetic rate (A), leaf water (Psi(w)), internal CO2 (C-i), osmotic (Psi(s)) and turgor (Psi(p)) potentials, transpiration rate (E), water-use-efficiency (A/E), stomatal conductance (g(s)) as well as F-v/F-m ratio. Among all wheat cultivars, cv. Lasani performed better in shoot and root fresh weight, and chlorophyll a contents at the tillering stage, while in MTS at the booting phase, cv. S-24 in shoot fresh weight, E, and g(s) at the boot stage and highest MTS and WUE at the tillering stage. However, cv. AARI-10 performed well in root fresh weight, Psi(w), Psi(s), Psi(p),, WUE and NPQ when stress was applied at the boot stage, while E and F-v/F-m in this cultivar on exposure to stress at the tillering stage. Cultivar Saher-2006 performed better in g(s), leaf Psi(s) and Psi(p) at the tillering stage, while F-v/F-m was recorded better at the boot stage and A in the same cultivar at all growth stages. Overall, HT stress applied at different growth stages was only effective in altering root fresh weight, MTS and NPQ in all four wheat cultivars. Of all wheat cultivars, cv. AARI-10 performed better in growth and physiological attributes examined in the present study under HT stress applied at different phenological stages.