Genetic Variation in Carbon Isotope Discrimination and Its Relation to Stomatal Conductance in Pima Cotton (Gossypium barbadense)

Abstract

Stable carbon isotope discrimination (Δ) was evaluated in primitive and cultivated Gossypium barbadense L. Significant differences among cultivated Pima lines were positively associated with the degree of selection for lint yield and heat resistance. A population mean study of a cross between B368, a primitive, uncultivated G. barbadense, and Pima S-6, an advanced line, showed that Δ is probably under genetic control, and could be a suitable selection trait in breeding programs. Eleven uncultivated accessions of primitive G. barbadense of varying origins grown in one environment showed a broad range of Δ values (18.8-20.50), pointing to substantial genetic variation of Δ in the G. barbadense germplasm. A was strongly correlated with stomatal conductance (g_s) in the commercial lines, a segregating F₂ population of the B368 × Pima S-6 cross, and the collection of uncultivated G. barbadense. This relationship indicates that variation in gs is the main source of variation for Δ in both uncultivated and commercial G. barbadense. The positive correlation between Δ, g_s and yield in the commercial Pima lines provides further evidence for selection pressures on higher g_s ensuing from selection for higher yield and heat resistance. Selection for higher Δ could increase yield in crops grown in hot, high irradiance, and well-irrigated environments.