Response of rice (Oryza sativa L. ) under elevated temperature at early growth stage: physiological markers

A reliable and rapid assessment technique, for evaluation of cultivars having potential to combat harsh environmental conditions is imperative. This experiment was carried out to screen 8 local (Pakistan) accessions of rice at early growth stage (germination and seedling) at control and heat shock for different time periods (24, 48, 72 h). Heat stress indices, including promptness index (P.I.) and germination stress index (G.S.I.), were used to explore thermotolerance at germination stage. At seedling stage, relative membrane permeability (RMP) were assessed through measurement of electrolyte leakage (EC), melondialdehyde (MDA) and production of hydrogen peroxide. It is observed that heat stress delayed germination and decreased germination percentage at germination stage. However cultivars showed significantly different response. Among all, "Kanwal-95" showed more thermotolerance in terms of maximum number of germination as well as in speediness to germination. Physiological indicators manifested, increased electrolyte leakage is associated with increased level of lipid peroxidation and hydrogen peroxide. It can be concluded that antioxidants enzymes could play major role in thermotolerance by scavenging free radicals to protect lipid peroxidation consequently improve cell membrane thermostability. Results analysis revealed that these indicators were simple and accurate selection criteria to assess heat stress effect and can be adopted to save resources and time of formers.