The search for traits related to drought resistance is a main step in the selection of cotton with improved performance under limited water supply. The effect of cultivar and drought conditions on the physiological traits, such as carbon isotope discrimination (Δ), photosynthesis (A), transpiration (E), stomatal conductance (gs), leaf osmotic potential (ψo) and leaf-water content (LWC), were studied in Andalucia, Spain. The morphological traits, such as leaf area and specific leaf weight (SLW), were also evaluated. In the initial study performed with three cottoncultivars, positive associations between Δ and A, E and gs were observed under increasing water stress. The A/gs ratio was negatively associated with Δ, and a strong negative correlation was observed between SLW and Δ. In a further experiment, using a wider group of cultivars, an apparent genotypic variation in Δ was observed in plants after withholding irrigation. Genotypic variation was found for gas exchange (A, E, gs) and leaf variables (LWC, SLW, ψo). No relationship was found between Δ and gas exchange or leaf-related traits. Considering both samplings as situations of different water availability, and plotting the data together, a low but positive correlation was observed between Δ and gs or LWC, and negative between Δ and A/gs. A remarkable correlation between LWC and gas exchange traits was found, whereas SLW was negatively correlated with A, A/E, and LWC. In dryland trials (1996 and 1997), the genotypic variation in LWC was positively associated with Δ. Under these conditions, an association between genotypic variation in Δ and A or A/E was observed. A positive correlation between yield and Δ was detected in 1996. Carbon isotope discrimination might be a useful tool for selecting drought-tolerant cotton genotypes but more studies are required to define more precisely the sampling conditions and the influence of factors affecting Δ and its relationship to crop yield.
Leidi, E.O.; Lopez, M.; Gorham, J.; Gutierrez, J.C. Variation in carbon isotope discrimination and other traits related to drought tolerance in upland cotton cultivars under dryland conditions. Field Crops Research (1999) 61 (2) 109-123. [DOI: 10.1016/S0378-4290(98)00151-8]