The influence of fiber molecular composition and structure on fiber strength is being evaluated. Immature cotton fiber samples from 1991 and 1992 from Mississippi Delta 51 ne (MD51ne) were compared with two commercial varieties, Deltapine 90 (DPL90) and DES 119. Three replicates for each variety were grown at Stoneville, MS, in a randomized complete block design. Bolls were harvested at 10 and 18 days post anthesis (DPA) and hand-ginned. Agronomic traits including locule weight, lint fresh weight, seed number, and seed weight, were measured at time of harvest. Ginned fiber from immature bolls (10 and 18 DPA) was stored in ethanol until dried for analysis. Mature fiber was obtained upon boll opening, and standard fiber properties were ascertained. Analysis of inorganic elements was carried out on the dry fiber by X-ray fluorescence. High performance liquid chromatography (HPLC) analyses were carried out on ethanol extracts of the fiber samples to identify carbohydrates and organic acids. Inductively Coupled Plasma (ICP) analysis was conducted on the same ethanol extracts for potassium, calcium, magnesium, and phosphorus concentrations.

Results from analysis of immature fiber (10 and 18 DPA) showed that varietal differences on selected traits are detectable at the earlier stage of development. Analysis of variance (ANOVA) was done on the three varieties (MD51ne, DPL90, and DES 119) using four variables (agronomic traits, X-ray fluorescence, HPLC, and ICP), and three stages of development (10 DPA, 18 DPA and mature cotton). Correlation analyses of the four variables were also made.

Dry fiber weight, percent dry weight, and dry weight/seed were significantly different for varieties at 10 DPA, but not at 18 DPA. In X-ray fluorescence analysis of fiber, Mg and K were significant on a per boll basis, while Mg, P, and K were significant on a per seed basis for different varieties. Ca was not significant among varieties in either case (boll or seed). At 18 DPA, no elements were significantly different among varieties. From ethanol extracts of fiber, the concentration of all sugars (sucrose, glucose, and fructose) were significant for varieties at 10 DPA expressed either on a per boll or per seed basis. Only sucrose and glucose (per seed) were significant according to variety at 18 DPA. From ethanol extracts of fiber, ICP results showed that all elements (Mg, P, K, and Ca) were significantly different among varieties at 10 DPA, but not at 18 DPA. Replication effects were not significant.

Results also showed that the elements Mg, P, and K are correlated to mature fiber elongation (E(1)) while sugar contents are correlated to mature fiber tenacity (T(1)). Therefore, the chemical composition/ properties of cotton fiber at an early stage of development can be a useful predictor of genotypes with high fiber strength at maturity.

Acknowledgements

The contributions of Andre Striegel, Linda Wartelle, and Elaine Champagne are gratefully appreciated.