QUANTITATIVE TRAIT LOCI AFFECTING COTTON FIBER ARE LINKED TO THE T(1) 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)t(1) lines with standard fiber characteristics. One hundred and forty-nine F-2-derived F-3 lines were developed from one cross, and 60 F-2-derived F-3 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.