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.