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New Evidence Relating the Pilose Allele and Micronaire Reading in Cotton

USDA-ARS, Cotton Physiology and Genetics Research Unit, P.O. Box 345, Stoneville, MS 38776

^* Corresponding author.

Experiments were undertaken to determine whether close linkage between the pilose allele and a locus influencing cotton (Gossypium hirsutum L.) fiber fineness had been misinterpreted as pleiotropy. Pilose (T₁), the dominant allele to the t₁ locus, is phenotypically described by a high density of trichomes on the leaf surface, the presence of trichomes on the carpel wall, and increased micronaire. Two lines, 239-17/6 and 250-14/2, were derived from single plant selections of pilose plants in an ‘Empire’ genetic background. 239-17/6 has atypically low micronaire readings. The 239-17/6 line was crossed to 250- 14/2, a pilose, high-micronaire line, and to lines carrying t₁ (normally pubescent) and T^sm₁ (glabrous). The F₁ plants were selfed for F₂ and backcrossefl to t₁ and T^sm₁ parents. Similar hybrids and backcrosses were made between 250-14/2 and t₁ locus recessives. The agronomic performance and fiber traits of 239-17/6, 250-14/2, Empire, and FTA (low micronaire check) were measured for 2 yr in replicated experiments. Lint yield, lint percent, and the fiber traits of elongation, maturity, micronaire, perimeter, span length, strength, and wall thickness were measured. 239-17/6 expressed a T₁ pilose phenotype. All 465 F₂ seedlings from 239-17/6 x 250-14/2 and reciprocal cross had tomentose leaves. The combined results from crosses of 239-17/ 6 and 250-14/2 with t₁ and T^sm₁, and backcrosses of F₁ to t₁ and T^sm₁ demonstrated that 239-17/6 and 250-14/2 both carry T₁. The fiber of 239-17/6 was not distinguishable from the fiber of either Empire or FTA for the wall traits of maturity, micronaire, and wall thickness. 239-17/6 was shown to have the T₁ phenotype and behave genetically like T₁. Since T₁ was associated with both high and low micronaire readings, the pleiotropic effect of T₁ on micronaire appears unlikely. A more likely explanation is the T₁ is linked to a gene or block of genes that influence micronaire.

Received for publication July 6, 1992.