Water stress reduces cellulose deposition in the cell wall and increases wax content, resulting in decreased fiber quality.

Introduction: Water deficiency reduces cotton fiber quality, but the underlying mechanisms behind this decline remain poorly understood. Although the cuticle is critical for plant water homeostasis under drought, few studies have addressed the relationship between water stress, fiber epidermal wax, and fiber quality. Thus, studying the interaction between fiber cuticular wax and quality is crucial for understanding plant drought tolerance and breeding superior drought-resistant cotton varieties. Methods: This experiment was designed as a randomized block design. Two cotton cultivars, Xincaimian7 (XC7, with high cuticular wax) and Shidamian217 (SD217, with low cuticular wax), were selected as materials. Two irrigation regimes were applied: well-watered (WW) and water-deficit (WD), each with three independent biological replicates. Results: Results showed WD irrigation significantly reduced the cotton fiber accumulation rate, particularly between 25-30 days post-anthesis (DPA). Compared with WW irrigation, the rate decreased by 23.62% and 30.82% respectively. WD treatment significantly inhibited the expression of the genes encoding sucrose synthase Discussion: In summary, WD reduces the sucrose content in cotton fibers and induces wax accumulation. Thinner cell walls combined with a thicker wax layer altered the mechanical properties of the fibers, thus leading to a decrease fiber quality. Therefore, when breeding drought-tolerant varieties, breeders need to balance the drought resistance with the sucrose and wax characteristics of the fibers.