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The distributions of breaking force and elongation of single fibers from five cultivated cotton varieties, African-51 ( G. herbaceum), Asian-163 ( G. arboreum), Maxxa and Texas Marker-1 ( G. hirsutum), and Pima-S7 ( G. barbadense), are studied. The range and distribution patterns of single fiber breaking force and elongation are significantly different for these cultivars and appear to be highly dependent on genotypes. Single fiber breaking force ranges from 16, 17, 20, 24, and 28 g for Pima-S7, TM-1, Maxxa, African-51, and Asian-163, respectively, and single fiber breaking elongation ranges from 16, 17, 18, 18, and 24% for these varieties. The single fiber breaking forces of Pima-S7 and TM-1 are symmetrically distributed, whereas those of the other three are asymmetrically distributed. African-51 and Maxxa have longer right tails, whereas Asian-163 has a longer left tail. Distributions of single fiber breaking elongation for all five varieties are asymmetrical and positively skewed, with the African and Asian cultivars having longer right tails. Within each cultivar, fibers of varying lengths have similar distributions in their breaking forces and elongation. This lack of relationship with fiber length suggests that these fibers’ tensile properties may be independent of length development, i.e., during elongation of the primary cell wall through the early stage of secondary cell wall synthesis. Single fiber breaking force and elongation are positively correlated ( r = 0.259 to 0.443) for all five varieties, with Pima having the highest correlation coefficient.

Variations in single fiber tensile properties of mature cotton fibers are investigated with respect to their association with seed positions and fiber-length groups within individual locules. Fibers from five varieties representing four cultivated cotton species (G. herbeceiitii, G. arboreion, G. hirsirtirnz, and G. barbadense) are included in this study. With the exception of G. arboreiittz, breaking forces, toughness, and linear density are highly dependent on the seed position in the locule, and the dependence is especially high for G. herbeceririz and G. barbadense. Fibers from seeds located closer to the main stem have higher breaking forces and linear densities, indicating their association with the distribution of nutrition resources. The relationships between single fiber tensile properties and fiber lengths vary among these cotton species. Breaking force and tenacity are independent of fiber length for G. barbadense, whereas fiber-length dependence is positive for G. herbeceiuii and G. arborewn, and there is a negative trend for the Maxxa variety of G. hirsirtirnz. For G. herbeceirm and G. arboreum, longer fibers have higher breaking forces, whereas the opposite is true for Maxxa. Single fiber breaking elongation decreases with increasing fiber length for all except G. barbadense. Overall variations of single fiber tensile properties are associated more strongly with the seed position in the locule than with the fiber length.Fiber length, strength, and fineness are commonly recognized as the most essential cotton fiber qualities by which mechanical processing (yam spinning, weaving, and knitting), product quality, and market value are determined. These cotton fiber qualities depend on a complex combination of factors associated with genotype and growth environment [l-3, 9-1 1, 141.Cotton fiber properties have been extensively studied, mostly by fiber bundle measurements because of the time-consuming nature of single fiber measurements [3]. Many have attempted to find the relationship between the mean values of single fiber properties and those of fibrous assemblies [3,5,[15][16][17]. The comprehensive fiber quality index (FQI) was introduced for this purpose [4, 12, 13, 151. Of all the qualities, fiber tenacity has been determined to be the chief fiber trait associated with yarn quality [3, 4, 151. Fiber bundle tenacity depends on individual single fiber ienacity as well as the uniformity of single fiber breaking elongation. If all fibers within a bundle have equal breaking elongation and no slack, the fiber bundle tenacity will be equal to the mean single ' Corresponding author: r w i l ylhsieh@ucdavis.edu, telephone (530) 752-0543. fiber breaking tenacity. In reality, bundle tenacity is lower because of the non-uniformity of fiber breaking elongation. The loss in bundle efficiency of tensile properties has been shown to range from 46% to 53%, depending on the uniformity of the fiber breaking elongation in the fiber bundles [17].To project product qualities, therefore, it is essential to have a better...

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