The inheritance of a basal branching type in guar

Abstract

Conflicting theories of inheritance of branching in guar [Cyamopsis tetragonoloba (L.) Taub.] have been reported. In this study, two lines differing in leaf surface and growth habit were used to make reciprocal crosses and form progeny populations in order to study how basal branching is inherited. Parents in the reciprocal crosses were PI 217923, which is an erect type with pubescent leaves that exhibits predominantly zero, but as many as four basal branches; and ‘Lewis’, which is a branching type with glabrous leaves that exhibits from two to ten branches at the base. Parental and progeny populations were evaluated for branching under field-grown conditions. Effect of plant spacing (seeding rate at 1 seed/cm vs. 1 seed/30 cm) on basal branching of PI 217923 and Lewis was studied. Hybrids were identified by erect branching and pubescent leaf surface. F₁ plants had erect branching type and pubescent leaves, indicating that erect branching is dominant to basal branching and there is no maternal effect. Chi-square goodness-of-fit analysis revealed that F₂ populations segregated in the expected 3:1 ratio (P<0.10–0.70), indicating that basal branching was controlled by one gene. We propose gene symbol Brh-1 for the gene that controls lack of branching as in segregating populations, Brh-1 is dominant to brh-1. Thus, the genotype of PI 217923 would be Brh-1/Brh-1 or Brh-1/brh-1 as it exhibits erect growth habit with little branching, while that of Lewis would be brh-1/brh-1. When grown at wider plant spacing (1 seed/30 cm), all branching increased, but 3 or 4 basal branches appeared in PI 217923, while the average number of basal branches in Lewis increased from 4.0 to 8.4.