Physiological and biochemical aspects of pre-sowing heat stress on cottonseed

An upland cotton (Gossypium hirsutum L.) cv. NIAB-78 was exposed to heat temperatures (40, 50, 60, 70 and 80°C) for eight hours. The stressed seeds were compared with untreated seeds for vigour evaluation using the standard procedures under laboratory and growth chamber conditions. Cottonseed oil analysis was carried out to evaluate the biochemical aspects of changes by pre-sowing seed treatments. Heat stress up to 70°C did not affect the final germination percentage, mean emergence time (MGT) and time taken for 50% germination (T₅₀), while no normal germination was recorded at 80°C. Heat stress upto 60°C significantly increased the seedling length and fresh and dry weights, cotyledon area and fresh and dry weights and hypocotyl length under laboratory and growth chamber conditions. Temperature stress beyond 60°C caused a decline in seedling vigour. Electrical conductivity of leachate from seeds stressed at 50 or 60°C was less than that of control seeds. The oil from all the stressed seeds except those exposed to 80°C had less free fatty acid percentage and peroxide value than the oil from untreated seed. Pre-sowing seed heat stress at 60°C for 8 h successfully enhanced the seed vigour thereby increasing the seedling vigour, while final germination percentage and time required to complete germination remained unchanged. Temperature stress of 80°C caused thermal injury to seeds and resulted in seed deterioration.