Drought and heat stress induce differential physiological and agronomic trait responses in cotton

Prolonged droughts and rising temperatures pose a significant threat to cotton yields, particularly during the crucial stages of flowering and boll development. Earlier studies have quantified the impact of individual effects of drought or heat. However, their interactive effects on the physiological and agronomic traits have been overlooked. In this study, twelve genetically diverse upland cotton cultivars were grown in four distinct growing environments: control (CNT), drought stress (DS), heat stress (HS), and the combined drought and heat stress (DHS) during the flowering and boll development stages. Findings reveal that the DHS has a more pronounced negative impact on plant health and yield-related traits than individual stresses. For instance, leaf temperature increased by 11 °C under DHS, 9 °C under HS, and 2 °C under DS compared with control-grown plants. Drought stress was more influential in reducing boll numbers with or without heat. Per °C increase in temperature decreased seed cotton yield by 12 % and 2 % with and without drought compared to CNT, respectively. Further, DS without heat reduced oil content by 10 %. Cultivars exhibited significant variations in physiology and agronomic traits under individual and combined stress. Most agronomic and physiological traits displayed a weaker association between control and combined stress. Moreover, the combined stress effects on most traits were not simply the sum of individual stress effects. This study highlights that single-stress tolerance alone may not be sufficient for optimal yields in hot and dry environments. Thus, breeding for improving cotton in hot and dry environments may need to prioritize combined stress tolerance as a distinct breeding objective. •The cotton reproductive stage is highly sensitive to hotter and drier conditions.•Cotton tolerates heat stress better than drought stress.•Tolerance to individual stress may not translate to combined stress tolerance.•Both heat and drought stress significantly impact cotton seed quality.•Cotton cultivars exhibited significant variation in combined stress tolerance.