Abstract
Thermal stress is a main limitation to achieve good and stable cotton yield in Pakistan. Cultivars differ in their adaptation to heat
stress. Therefore, the screening of advanced strains is carried out by planting cotton in the month of April to coincide their fruiting
phase with the hottest period of season (June-July). Fourteen genotypes were selected for screening against heat stress. Seed sowing
was done during mid-April and the leaves were collected after 90 days of sowing while seed cotton yield was taken 125 days after
sowing. Results revealed that genotypes CIM-496, Cyto-87, NIAB-V3, CIM-554, NIAB-V1 and CIM-541 resulted in higher seed
cotton yield while Gomal 93 and Shahbaz, CRIS-342 and Cyto-89 exhibited lowest seed cotton yield. It was also observed that heat
induced-stress caused certain quantitative and qualitative changes in phenolic, sugar and protein contents. The quantitative changes in
the amounts of crude protein were also observed and such changes varied variety to variety but not in a regular fashion. Different
types of sugar compounds were observed in all cultivars with no distinct relation with seed cotton yield. It was found that higher
yielding cultivars maintain relatively higher nitrogen and protein contents and less sugar contents as compared to low yielding
cultivars under high temperature environments. In qualitative analysis of phenolic contents, six standards phenolic compounds namely
gallic acid, pyragallol, hydroquinone, phenol, 2-naphthol and o-nitro phenol were detected in different cultivars of cotton, indicating
that high day temperature cause various changes in the metabolism of the plant helpful for their adaptation under arid climate
