Chemical variation for fiber cuticular wax levels in upland cotton (Gossypium hirsutum L.) evaluated under contrasting irrigation regimes

The fiber from upland cotton (Gossypium hirsutum L.) makes up approximately 90% of the global cotton produced each year. Fiber quality is important to textile mills for processing and factors into bulk cotton sales. Fiber quality can be affected by many environmental factors, including water deficit, which makes identifying major fiber characteristics an important focus for breeding programs. Cotton fibers are specialized trichomes that are primarily composed of cellulose but have a cuticle composed of free waxes and cutin. Total cuticular wax of cotton fiber has been shown to act as a lubricant during textile processing, but has also been negatively correlated with important quality traits. The objectives of this study were to identify and quantify the cuticular wax compounds of cotton fiber under water-limited (WL) and well-watered (WW) irrigation treatments and assess their relationship with fiber quality from seven upland cotton lines. Through the most detailed characterization of cotton fiber cuticular wax to date, 41 quantifiable compounds were identified including free fatty acids, primary alcohols, aldehydes, alkanes, and tentatively identified alkanediols. Of these 41 compounds and their sum (total waxes), the abundance for nine were significantly different (α = 0.05) between WL and WW conditions. Total wax and 36 compounds were highly repeatable (r ≥ 0.60), indicating they will respond positively to selection in cotton breeding programs. Irrespective of irrigation regime, strong positive correlations (rp 0.64-0.80) were found for fiber length and uniformity with primary alcohols, fatty acids, and aldehydes. These findings suggest that the biosynthetic pathways associated with these compounds are contributing to the phenotypic variability of these two important fiber quality traits and thus the biochemical pathways associated with cuticular fiber wax are candidates for metabolic engineering via molecular breeding approaches.