Variable Expressivity and Gene Action of Gland-Determining Alleles in Gossypium hirsutum L.1
- F. D. Wilson and
- J. N. Smith2
We studied the variable expressivity of gland-determining alleles at three loci in stigmas and bolls of cotton (Gossypium hirsutum L.) and their effects on the amounts of flower-bud (square) gossypol that occur those glands. High levels of square gossypol provide resistance in the plant to certain insect pests. The alleles gl1 and gl1y reduced stigma-gland density and square gossypol content slightly but rendered bolls glandless, or nearly glandless. The Gl2 allele was more expressive than Gl3 for boll gland density and seed-gossypol content, but less expressive for stigma-gland density and square gossypol content. The relative potency of three alleles at the gl3 locus was Gl3'>Gl3ru1>Gl3. Judicious combinations of alleles should maximize gossypol content in the squares without changing it as much in the seeds. The alleles Gl2, Gl3, and Gl3rui repressed the gland-determining action of the high-potency Gl3' because F1 means were below the midparental value (MP) when any one of these alleles was present, but above MP when they were absent in combinations carrying Gl3'. All F1 combinations carrying Gl3 had lower amounts of square gossypol than MP. Additive genetic effects were similar and predominant in a halfdiallel set that included four parents and their hybrids carrying all combinations of Gl2, gl2, Gl3, and gl3, and in a diallel set to which had been added a fifth parent and hybrids carrying Gl3'. Nonadditive effects, however, differed for gland density, emphasizing the variable action of these alleles in different parts of the plant. The halfdiallel analysis showed only additive effects for square gossypol content, but the F1. —MP relationship indicated that nonadditive effects were also present. Thus, direct selection for high gossypol content, even though much more efficient than selecting for high gland density, could still present some breeding problems.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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