Quantification of Leaf Wax and Cutin Compounds for Improved Drought Tolerance in Upland and Pima Cotton

Climatological drought is a historic problem that limits agricultural production worldwide. Reducing transpirational water loss can conserve soil moisture and confer drought tolerance to crops by delaying dehydration during periods of drought stress. Transpiration can be regulated by the hydrophobic plant cuticle, which coats the aerial surfaces of plants and limits water loss through nonstomatal transpiration. The cuticle is composed primarily of two lipid classes, the nonpolymerized cuticular wax components and the cutin polyester. Many studies suggest that both waxes and cutin are important in maintaining plant water potential during periods of drought. Five pima and six upland cotton lines were grown in a controlled environment to determine if leaf wax and/or cutin differs among cotton germplasm and species. Three leaf disc samples were collected from each line for wax and cutin extraction. Wax was extracted with chloroform and analyzed with an Agilent 7890A gas chromatograph mass spectrometer (GC-MS). Cutin was extracted following a standard soxhlets method before analysis on the GC-MS. Results show that upland cotton develops more total wax while pima cotton develops more total cutin. This shows an interesting deviation in nonstomatal water loss prevention mechanisms between the cotton species. In both species, alcohols were the most abundant wax compounds and dihydroxy monobasic acids were the most abundant cutin compounds. Analysis with canopy temperatures from field grown plants shows Pearson correlation coefficients ranging from -0.41 - -0.80 with total wax while total cutin ranged from -0.05 – 0.35. This indicates leaf cuticular wax would be a good breeding target for reducing water loss through nonstomatal transpiration in cotton.