Role of Photosynthetic Rate and Transpiration Efficiency in Fibre and Lint Yield Improvement of Upland Cotton Genotypes in Clay-Loamy Soils

Abstract

Upland cotton (Gossypium hirsutum L.) is a critical economic and most valued crop in Pakistan, yet its lint yield remains below global benchmarks, particularly in challenging environmental stresses. This study evaluated the role of key physiological and agronomic traits in improving lint yield and fiber quality among ten genotypes (BH-249, BH-299, BH-226, BH-254, BH-306, BH-224, BH-188, BH-345, BH-184, and CIM-600) at the Cotton Research Station, Bahawalpur, using a Randomized Complete Block Design with three replications. Significant genotypic variation (p ≤ 0.01) was observed for physiological traits, with photosynthetic rate (24.64–30.33 µmol m⁻² s⁻¹) and stomatal conductance (257.6–340.3 mmol m⁻² s⁻¹) strongly correlated with lint yield (r = 0.50* and 0.95**, respectively). BH-226 achieved the highest yield at 4.56 ± 0.24 t/ha, driven by superior sympodial branching (21.66 ± 2.02) and opened bolls (55.3 ± 6.06), while BH-249 and BH-299 excelled in physiological efficiency. Principal Component Analysis revealed that PC1 and PC2 explained 59% of the variance, with yield aligning closely with sympodial branches and photosynthetic traits, indicating a strong correlation between them. Fiber quality traits like length (28.53–29.16 mm) and strength (29.5–32.5 g/tex) showed moderate associations with physiological parameters, but a trade-off was noted between fiber fineness and ginning out-turn (r = -0.66*). These findings highlight the potential of selecting genotypes with enhanced photosynthetic and transpirational efficiencies to boost lint yield in Pakistan’s clay-loamy soils, offering a pathway to bridge the yield gap with global leaders like China (1,992 kg/ha) while maintaining fiber quality.