Pigment gland expression in Gossypium interspecific hybrids

The pigment glands in cotton impart a degree of insect resistance to the plant, however, the terpenes in the glands also make the seeds toxic to non-ruminant animals. An ideal cotton plant would have many large glands in the foliage, but would have no glands in the seeds. While both of these traits occur individually in different wild Gossypium species, they do not occur in upland cotton. Gossypium sturtianum has a nearly glandless embryo that forms glands upon germination. The foliage glands of Gossypium anomalum are both large and numerous with the boll glands being especially large. The objective of this study was to examine the expression of these traits when the wild species are hybridized with cultivated cottons. A second objective was to determine, if possible, what type of inheritance controls the trait expression.

To evaluate the gland seed trait, three generations of seeds of hexaploid hybrids involving cultivated cotton and G. sturtianum were examined. A wide and continuous range in gland expression among seeds was noted, and in order to group seeds of similar phenotypic expression, four categories were established: very few glands (vfg), few glands (fg), several glands (sg), and glanded (gld). Selected seeds from each category in the first and second generations examined were germinated and grown to maturity. The gland densities in leaf, bract, and stem samples were examined on individual plants. The density of glands in the vegetative portions of the plant was independent of the seed gland category from which it descended.

Under field conditions seed set of the hybrids was very low and segregation ratios could not be determined. However, sufficient seed were obtained to establish that the inheritance of seed gland density is quantitative.

To evaluate the large foliage gland trait of G. anomalum, leaf gland expression in F₁ and F₂ generations of an intergenomic cross between Gossypium arboreum and G. anomalum was studied. The mean leaf gland density of F₂ plant samples was larger than the mean leaf gland density of F₁ and G. arboreum leaf samples. The range in leaf gland density was greater for the F₂ plants than for F₁, G. arboreum, and G. anomalum leaf samples. The wide range observed among F2 plants indicates quantitative inheritance for the trait.

The results of this study indicate the possibility of intro-gressing the near glandless trait of G. sturtianum and the large vegetative gland trait of G. anomalum into commercial varieties of cotton. Both traits appear to be quantitatively inherited and selection pressure for these traits in hybrids of wild and commercial cotton may ultimately result in the ideal commercial and agronomic goals of glandless seeds and heavily glanded vegetative parts.