Effects of Plant Smoothness on Agronomic Traits of Upland Cotton—Lint Percentage1

Abstract

In attempts to document agronomic deficits associated with plant smoothness in cotton (Gossypium hirsutum L.), two complete diallel sets involving various combinations of smoothness and pilosity alleles were grown in randomized, complete blocks at two locations in North Carolina in 1982. There were four replications per location. The first diallel was generated by intercrossing stocks homozygous for the allelic pairs Sms11 and sml, and Sm2 and sm2, and the second from intercrossing Sm2 and sm2, and Sm, and smh3. Increasing the number of Sm alleles increases plant smoothness, whereas the completely recessive genotype (all sm alleles) determines normally pubescent, the phenotype of ‘Coker 310’, the cultivar used as background. Within the two diallels, lint percentage varied from 38.1 to 43.3 with the lowest values associated with the Sm2 allele, and the highest involving a hybrid of Sms11 and sm1. Although the Sms11 allele was associated with a small deficit in lint percentage when homozygous, only the Sm2 allele was accompanied by significant deficits, and that related to relatively low lint index. Number of seeds per boll, seed index (weight of 100 seeds, g), lint index (lint per 100 seeds, g), and grams of seed cotton per boll varied significantly among some entries. There was no evidence that values for any of these traits tracked degree of plant smoothness. Mostly additive effects were associated with significant contrasts for most of the traits, although there were some significant interaction effects, particularly with the Sm2 and sm2 pairs of alleles. There was no evidence that increasing plant smoothness to the point of eliminating trichomes reduced lint percentage any lower than that associated with the Sm2 monomeric genotype.