POD CHARACTERISTICS INFLUENCING CALCIUM CONCENTRATIONS IN THE SEED AND HULL OF PEANUT

Calcium is often a limiting factor in peanut (Arachis hypogaea L.) production. Since the peanut fruit develops underground, it will not transpire root absorbed water. Therefore, the developing fruit must absorb phloem-immobile ions such as Ca directly from the soil solution. This experiment''s objective was to determine the influence of several pod characeristics on Ca accumulation and Ca concentration in peanut fruit. Eight genotypes with diverse fruit characteristics were grown for two seasons under five water stress treatments [drought 20 to 50 d after planting (DAP), 50 to 80 DAP, 80 to 110 DAP, 110 to 140 DAP, and a well-watered control]. The 80- to 110-DAP drought period had the greatest negative impact on seed Ca concentrations. Total Ca accumulation in the pod (hull + seed) was positively correlated (0.97) to pod surface area. However, five pod characteristics (days required to mature a pod, specific hull weight, pod surface area, hull thickness, and pod volume) significantly influenced seed and hull Ca concentrations. These characteristics were under genetic control, but their absolute value was modified by water stress. Supply of Ca to the seed may be analogous to a filter system. Thin, light hulls and long pod maturity periods promote high Ca concentrations in the seed. Thick, dense hulls, short maturity periods, and small pod volumes promote high Ca concentrations in the hull.