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Effects of Plant Smoothness on Agronomic Traits of Upland Cotton—Fiber Properties¹

Glabrousness in upland cotton (Gossypium hirsutum L.) confers resistance to certain insects and decreases trash in ginned lint. Such plant smoothness has been associated with reductions in lint percentage and fiber yield, but there is little information on the effects of the phenotype on fiber properties. Two complete diallel sets involving various combinations of smoothness and pilosity alleles were grown in randomized, complete blocks in North Carolina in 1982 in four replications per location. The first set was generated by intercrossing the allelic pairs, Sm^s1₁ and sm₁, and Sm₂ and sm₂ in all possible combinations, and the second by intercrossing the allelic pairs Sm₂ and sm₂, and Sm, and sm⁴₁. Increasing the number of Sm alleles in a given cotton increases plant smoothness, whereas the completely recessive phenotype (all sm alleles), imparts normally pubescent, the phenotype of ‘Coker 310’, the cultivar used as background. Within the two diallels 2.5% fiber span length varied from 26.9 to 30.1 mm with the lowest values associated with the Sm₂ allele. Fifty percent span length varied from 13.0 to 14.3 mm but was significantly various only in the first diallel, and the variation for 50% span length in that particular set did not relate to degree of plant smoothness. The entries with the shortest 2.5% span length tended to have the highest fiber uniformity index. Micronaire values above 5 were associated with some of the entries homozygous for Sm₂ and fiber tenacity showed a deficiency where the Sm^s1₁ allele was homozygous. There were significant estimates for general and specific effects for some of the traits, particularly with entries harboring the Sm₂ x sm₂ contrasts, and evidence for maternal and reciprocal (maternal x embryonic) effects for some traits. There was no consistent evidence that degree of plant smoothness related to disturbances in any fiber trait, but evidence that specific smoothness alleles were accompanied by fiber quality deficits.

Key Words: Gossypium barbadense L. • Gossypium hirsutum L. • Gossypium tomentosum Nutt. ex. Seem. • General Effects • Specific Effects • Maternal Effects • Reciprocal Effects • Trichomes

² Geneticist, USDA-ARS and professor of crop science, North Carolina State Univ., Raleigh NC 27650.

Received for publication September 22, 1983.