Genetical Studies Concerning The Distribution Of Trichomes On The Leaves Of Gossypium hirsutum.

The species, Gossypium hirsutum L., displays a variety of phenotypes with regard to the distribution of trichomes on the leaves and stems of mature plants. The fully pubescent, or normal, phenotype is determined by the concerted action of alleles from at least three loci. These loci also bear alleles that remove trichomes from leaves and stems. Each smooth-leaf allele, when homozygous and acting free of other smooth-leaf alleles, removes a portion of the trichomes from a leaf, leaving the remaining trichomes distributed in a characteristic pattern. Various combinations of smooth-leaf alleles at different loci act cumulatively to remove more trichomes, and certain combinations remove all trichomes from foliage and stems. An unknown number of alleles of small effect, at other loci, alter the density of pubescence on normal cottons. Apparently these same alleles alter the phenotypes of some of the smooth-leaf alleles but not others. The genetic variability isolated and described was sufficient to generate most of the spectrum of phenotypic variability for the character, degree of pubescence density, that has been observed in G. hirsutum.