Does the Cotton Cultivars' Water Use Vary Based on the Stomatal Conductance Response to High Vapor Pressure Deficit Under Rainfed Conditions?

In West Tennessee, approximately 92% of cotton production is dryland. Producers have few options to mitigate drought stress on dryland acres; most must cope with drought stress by either adopting cultural practices which increase water use efficiency or by selecting drought tolerant cultivars. During 2017, a study was conducted at the West Tennessee Research and Education Center (WTREC) in Jackson, TN to identify drought tolerant cultivars based on the presence of a limited transpiration trait (TR_lim), and to monitor other physiological parameters including: leaf water potential (LWP), relative water content (RWC), stomatal conductance (gs), water use efficiency coefficient (WUE_k) and wilting score (WS) under rainfed conditions. Therefore, six cultivars of varying maturities were grown under rainfed conditions with for replications. Differences were observed among cultivars in their expression of the TR_lim trait with increasing vapor pressure deficit (VPD) in the field environment (max VPD: ~ 5 kPa). Only PHY 490 W3FE (Dow AgroSciences, Indianapolis, IN) expressed the TR_lim trait but interestingly, this cultivar closed stomata partially under 2.2 kPa-VPD and high temperature (>90⁰ f). Furthermore, this cultivar showed significantly lower WS (0.3), reduced g_s (0.54 mol H₂O m^–2s^–1), and higher WUE_k (6.3 Pa) compared to the other cultivars. Although, PHY 490 W3FE was also characterized by numerically higher LWP and RWC, differences were not statistically significant. Cultivars PHY 330 W3FE (Dow AgroSciences) and ST 6182 GLT (Bayer CropScience; Leverkusen, Germany) showed the highest WS and lowest LWP. Additional research should be conducted to investigate these cultivars in controlled environment under different levels of VPD to understand if high temperatures in the field trial prevented other cultivars from expressing the TR_lim/water saving potential.

Keywords; cotton, rainfed, limited transpiration trait (TR_lim), leaf water potential (LWP), relative water content (RWC), stomatal conductance (gs), water use efficiency coefficient (WUE_k), wilting score (WS)