Impact of heat stress responsive factors on growth and physiology of cotton (Gossypium hirsutum L.).

Pakistan ranked highest with reference to average temperatures in cotton growing areas of the world. The heat waves are becoming more intense and unpredictable due to climate change. Identification of heat tolerant genotypes requires comprehensive screening using molecular, physiological and morphological analysis. Heat shock proteins play an important role in tolerance against heat stress. In the current study, eight heat stress responsive factors, proteins and genes (HSFA2, GHSP26, GHPP2A, HSP101, HSC70-1, HSP3, APX1 and ANNAT8) were evaluated morphologically and physiologically for their role in heat stress tolerance. For this purpose, cotton crop was grown at two temperature conditions i.e. normal weather and heat stress at 45 °C. For molecular analysis, genotypes were screened for the presence or absence of heat shock protein genes. Physiological analysis of genotypes was conducted to assess net photosynthesis, stomatal conductance, transpiration rate, leaf-air temperature and cell membrane stability under control as well as high temperature. The traits photosynthesis, cell membrane stability, leaf-air temperature and number of heat stress responsive factors in each genotypes showed a strong correlation with boll retention percentage under heat stress. The genotypes with maximum heat shock protein genes such as Cyto-177, MNH-886, VH-305 and Cyto-515 showed increased photosynthesis, stomatal conductance, negative leaf-air temperature and high boll retention percentage under heat stress condition. These varieties may be used as heat tolerant breeding material.