Gene Action in the Inheritance of Fiber Properties in Intervarietal Diallel Crosses of Upland Cotton, <i>Gossypium hirsutum</i> L.¹

Abstract

We grew nine selected cotton varieties, all possible F 1 hybrid combinations among these varieties, and their corresponding F 2 's in a split‐plot design with four replications. Heterosis, when measured as the departure from the average midparent value, was manifested at a low level for 50% span length (4.0%), 2.5% span length (2.8%), fiber strength (5.6%) and fiber elongation (8.5%). Heterosis was not observed for fiber fineness. Inbreeding depression, measured as a reduction in F 2 below F 1 performance, was not significant for any of the fiber properties measured. General and specific combining ability were both highly significant for all fiber properties. Jinks‐Hayman's method of diallel cross analysis showed that all fiber properties were within the range of partial dominance (except fiber fineness, which showed overdominance, possibly caused by repulsion linkage) and that all are polygenically inherited characters. Heritability, as the ratio of the additive, or additive ✕ additive epistatic variance, or both, to the total phenotypic variance, was relatively high for all fiber properties measured, except fiber fineness. This result suggested that a major part of the total phenotypic variance was additive.