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Short-Branch and Cluster-Fruiting Habit Inheritance in Crosses of Eight Cotton Lines¹

The potential value of fruiting branches (sympodia) of intermediate length in an ideotype for a high-yielding line of F₁ hybrid cotton grown for stripper harvest led us to research for modifier genes that affect the expression of alleles at the two known major gene loci (cl₁ and cl₂ that exert primary control over sympodial length. Six stocks of Gossypium hirsutum L., and two G. barbadense L. stocks representing three basic branching habits, normal (Cl₁ Cl₁ Cl₂ Cl₂), cluster (cl₁ cl₁ cl₂ cl₁ Cl₂), and short branch (Cl₁ Cl₁ cl₂ cl₂), were crossed in all possible one-way combinations to assess the expression of the mutant alleles in the F₁ generation in various genetic backgrounds. Lateral internode distance to the first fruiting form (square) was measured at the ninth vertical node in the parental and F₁ field-grown populations. Twenty of the 25 crosses showed full dominance of the normal allele over the mutant allele. However, five of the crosses were bimodal with a progeny class of intermediate length occurring in addition to a dominant normal length class. This was interpreted to mean that one or both of the parental lines involved harbored a gene that modified the dominance relationships between the normal and mutant genes conditioning sympodial length. Modified activity in cluster (cl₁) expression was observed in four crosses, and modified short-branch (cl₂) expression was detected in one cross.

Key Words: Gossypium hirsutum L. • G. barbadense L. • Monogenic inheritance • Modifier genes

² Former graduate research assistant and professor, respectively, Dep. of Crop and Soil Sciences, New Mexico State Univ., Las Cruces, NM 88003.

Received for publication November 22, 1983.