Quantitative Trait Loci Affecting Cotton Fiber Are Linked to the T1 Locus in Upland Cotton

Pilose (T 1), a dominant marker in upland cotton, has been associated with coarse, short fibers. Pilose was, thereby, considered to be pleiotropic on fiber fineness and length. However, a pilose-expressing line with a fiber of average fineness was recently identified. This finding does not support pleiotropy between T 1 and fiber traits, but is indicative of linkage between pilose and loci influencing fiber characteristics. To understand the relationship between T 1 and fiber traits, a pilose line with short, coarse fiber was crossed to two t 1 lines with standard fiber characteristics. One hundred and forty-nine F2-derived F3 lines were developed from one cross, and 60 F2-derived F3 lines from the other. Seven fiber traits (elongation, maturity, micronaire reading, perimeter, 2.5% span length, strength, and wall thickness) were measured. Segregation was normal, as indicated by allelic frequencies of 0.5 for T 1 and t 1, and segregation ratios of 1∶2∶1 for marker genotypes. The association of homozygous T 1 lines with fibers of average fineness was again observed. Linkage between T 1 and loci affecting micronaire, perimeter, 2.5% span length, strength, and wall thickness was found in both populations. Significant additive and non-additive gene effects for each of these traits at the marker locus were found as well. The pilose marker accounted for 10-75% of the phenotypic variation associated with each trait. In conclusion, the t 1 locus is linked to numerous loci that influence fiber traits, and this linkage has previously been misinterpreted as pleiotropy.