Inheritance of High Glanding, an Insect Resistance Trait in Cotton
The high glanding (HG) trait [i.e., presence of gossypol glands the upper edge of the sepals of the upland cotton (Gossypium hirsutum L.) flower bud] confers a significant level of resistance to bollworm [Helicoverpa zea (Boddie)] and tobacco budworm [Heliothis virescens (F.)], but the inheritance of this trait is not well understood. The objective of this study was to determine the inheritance of the HG trait to aid breeders in developing improved HG cultivars. Crosses were made among HG, normal glanding (NG), and glandless genotypes, and with isolines of the HG breeding line, XG-15, which had genotypes 2(Gl2 gl3) and 2(gl2 Gl3). The isoline, XG-15 gl2Gl3, expressed the HG phenotype, leading to the hypothesis that HG is conferred by a special Gl3 allele derived from XG-15. Crosses of HG × NG parents resulted in HG F1, 3 HG/1 NG ratios in the F2, and ratios of 1 HG/2 segregating/1 NG among F2:3 progeny. Crosses of XG-15 gl2Gl3 × NG produced similar results. The cross, XG-15 gl2Gl3 × HG, did not segregate for calyx margin glanding type. The cross, XG-15 gl2Gl3 × glandless, resulted in glandless flower buds in the F1 and a ratio of 3 glandless (flower buds)/1 HGin the F2. The F1 HG × glandless had small sparse glands on the base of the sepals. Phenotypes of individual F2 plants did not appear to fit common segregation ratios, but data from F2:3 families supported the hypothesis that a special Gl3 allele confers the HG phenotype. This allele, derived originally from Socorro Island cotton, is tentatively designated GlS3.
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