Evaluation of Upland Cotton (Gossypium hirsutum L.) Genotypes for Heat Stress Tolerance Based on Physiological and Agronomic Parameters in Multan, Punjab

Abstract

Heat stress poses a significant threat to cotton production in Pakistan, particularly in the southern Punjab region where temperatures frequently exceed 45°C during the reproductive phase. The present study was conducted at Multan, Punjab, Pakistan to evaluate fifteen upland cotton genotypes for heat tolerance during 2025-2026 growing season. A comprehensive screening protocol involving cell membrane thermo stability (CMT), germination percentage under heat stress (45°C), in vitro pollen viability, chlorophyll content (SPAD), relative water content (RWC), proline accumulation, shoot and root length, boll retention percentage, and seed cotton yield was employed. Based on heat susceptibility index (HSI), genotypes were categorized into tolerant (HSI ≤ 1.00) and moderately tolerant (1.00 < HSI ≤ 1.50) groups. The analysis of variance revealed significant differences (P < 0.01) among genotypes for all studied traits. Results indicated that Gossypium hirsutum genotypes FH-Noor, FH-Lalazar, NIAB-878, MNH-886, NIAB-545, BH-167, and IUB-13 exhibited superior heat tolerance with HSI values ranging from 0.627 to 0.923. These genotypes maintained lower cell membrane injury (33.25-38.77%), higher germination percentage (73.17-79.33%), enhanced pollen viability (62.60-69.83%), and superior chlorophyll content (39.02-41.69 SPAD) under heat stress conditions. Conversely, genotypes IR-6, CIM-632, CIM-602, CIM-496, VH-363, FH-142, FH-152, and MNH-992 were classified as moderately tolerant with HSI values between 1.043 and 1.488. Correlation analysis revealed significant positive associations of seed cotton yield with germination (r = 0.973), boll retention (r = 0.952), relative water content (r = 0.952), and chlorophyll content (r = 0.952), while significant negative correlations were observed with cell membrane injury (r = -0.963) and proline content (r = -0.943). Principal component analysis demonstrated that the first two components explained 96.2% of total variation, with seed cotton yield, germination percentage, and boll retention contributing most to PC1. These findings provide valuable insights for developing heat-tolerant cotton varieties suitable for cultivation in the arid and semi-arid regions of southern Punjab, Pakistan.