Salt sensitivity of cowpea at various growth stages

Summary

The relative salt tolerance of cowpea (Vigna unguiculata (L.) Walp. cv. California Buckeye No. 5) at different stages of growth was determined in a greenhouse. Plants were grown in sand cultures that were irrigated four times daily with modified half-strength Hoagland's solution. Salination with NaCl and CaCl₂ (2:1 molar ratio) provided seven treatment solutions with osmotic potentials (Ψ_s) ranging from −0.05 to −1.05 MPa (electrical conductivities of 1.4 to 28 dS/m). Salt stress was imposed for 20 days beginning at either 7, 27, or 52 days after planting. The three 20-day stages are referred to here as vegetative, flowering, and pod filling stages. Pod and seed yields from plants stressed during either the vegetative, flowering, or pod-filling stages indicated that cowpea was the most sensitive to salinity during the vegetative stage and became less sensitive the later plants were stressed. Seed yield was reduced 50% at Ψ _s =−0.45, −0.76, and −0.88 MPa for plants salinized during the vegetative, flowering, and pod-filling stages, respectively. Salinity reduced seed yield by reducing seed number; it had little, if any, effect on the weight of individual seeds. Vegetative growth was significantly reduced by salt stress during all three stages but the effect was much less when stress was imposed during the last two stages than during the first stage.