Heat Tolerance Screening Studies and Evaluating Salicylic Acid Efficacy against High Temperature in Rice (Oryza sativa L.) Genotypes

High temperature retards plant growth and development. Major objective of this study was to assess heat tolerant potencies of forty rice cultivars at seedling stage and check the effectiveness of salicylic acid (SA) in improving thermo-tolerance. Rice seeds were sown in plastic bowls containing sand and heat stress (45°C) was applied on 15- days old seedlings for 12 and 24 h in growth incubators. Growth related stress tolerance indices were used as screening tools. Among all, two heat sensitive (Rambir and DM 15-1) and heat tolerant (RP2 and DM1-30-15-04) cultivars were selected for SA studies. SA spray (100 mg L-1) was used on 15-days old seedlings and heat stress (45°C) was imposed on 19-days old seedlings for 12 h and 24 h. Growth (root and shoot lengths and fresh and dry biomasses) and biochemical attributes (nitrate and nitrite reductase, total soluble sugars, proteins, nitrogen, potassium, phosphorous and magnesium) were measured. Heat shock reduced seedling growth, enzymatic activities and mineral contents. However, SA enhanced fresh and dry biomass, concentration of organic and inorganic solutes in all genotypes under heat stress. SA improved thermo-tolerance in RP2 and DM1-30-15-04 genotypes. These heat tolerant genotypes have capability to give better seedling growth and stand establishment.