Screening cotton cultivars under induced water-deficit stress in controlled environments and field settings: expression of drought tolerance traits

Cotton (Gossypium hirsutum L.) is often grown in climates of intermittent drought conditions. Plants that limit transpiration rates (TRs) when initially exposed to water-deficit stress will preserve water for use later during critical growth stages. Two traits resulting in conservative TRs are TR limitations under soil drying and high vapor pressure deficit (VPD, >2.5 kPa). The objective of this study was to assess the performance of four contrasting cotton cultivars and their TRs under induced water stresses. Three studies were conducted to test (i) the early stomatal closure under soil drying in a greenhouse, (ii) the TR to varying VPD levels in a growth chamber, and (iii) the stomatal conductance (gs), wilting score, specific leaf area (SLA), relative water content (RWC), and yield in an extreme field environment. Significant differences in the fraction of transpirable soil water threshold (FTSW threshold) were detected among cultivars in the greenhouse. The FTSW threshold among cultivars ranged from 0.29 to 0.39. Under varying VPD levels, only PHY 400 W3FE expressed a limited TR (TRlim) with increasing VPD at 1.6 kPa. In the field study, differences in gs, wilting score, RWC, SLA, and lint yield were observed among cultivars within the water limited treatments (i.e. rainout and rainfed). PHY 400 W3FE had the lowest wilting score compared to other cultivars. Under the rainout treatment, PHY 400 W3FE yielded 37% higher than PHY 500 W3FE. Results indicate a trend in water saving potential among cotton cultivars, given the differences in their TR sensitivity to water-deficit stress conditions.