NEW EVIDENCE RELATING THE PILOSE ALLELE AND MICRONAIRE READING IN COTTON

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 T1sm (glabrous). The F1 plants were selfed for F2 and backcrossed to t1 and T1sm 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 T1sm, and backcrosses of F1 to t1 and T1sm 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.