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EXPRESSIVITY OF H₂ GENE OF HAIRINESS AND L_° GENE OF LEAF SHAPE OF COTTON UNDER DIFFERENT GENETIC BACKGROUNDS

HAFEEZ-UR-RAHMAN AND WAHEED SULTAN KHAN

Abstract: The expressivity of H₂ gene of hairiness (pilose) and L_° gene of leaf shape in cotton (Gossypium hirsutum L) was studied in F₁ and F₂ generations of four crosses involving a female Okra Pilose strain (HR-Velvet Okra) and four broad leafed and semi/sparsely hairy varieties/strains of cotton. Both pilose and okra leaf shape of cotton plant were partially dominant in F_l generation. The F₂ generations of all the four crosses segregated into four classes of hairiness as well as that of leaf shape. The summation of the two intermediate classes of leaf hairiness and shape helped to fit the segregating classes of three crosses to the theoretical 1 :2: 1 ratio of partial dominance. The two homozygous extreme classes of both the characters were easily distinguishable however, the heterozygous condition for hairiness was highly influenced by the genetic background i.e., modifying gene effect. It was perceptible from the study that hairiness and leaf shape in cotton though monogenically inherited, their phenotypic expressions especially in heterozygous conditions were affected by a complex.of modifier genes (genetic background) especially that for pubescence. Hairiness, as compared to leaf shape was more influenced by the minor (modifier) gene effect. Homozygous condition for both H₂ and L_° genes, however, imparts pilose hairiness and narrow okra leaf shape, respectively, without the aid of modifier genes. A significant level of genetic association (linkage) existed between H₂ and L_° genes in two crosses; HRVO x S-12 and HRVO x S-14, which was indicative of the higher number of velvet okra combi lation in the advance segregating generations of these crosses.

Cotton Research Institute, Faisalabad, Pakistan.