Genotypic variation for phosphorus uptake from hardly soluble iron- phosphate in groundnut (Arachis hypogaea L.)

Abstract

This study was aimed at assessing genotypic variation for phosphorus (P) uptake from Fe–P in groundnut (Arachis hypogaea L.). Of twenty genotypes evaluated in an initial screening experiment, three were chosen for further studies to investigate potential mechanisms responsible for the observed differences in P uptake. Wasedairyu (high uptake) and Kintoki and ICGV 87358 (low uptake) were grown in 2-1 pots on Vermiculite–Fe–P and sampled after 50, 85 and 115 days. Wasedairyu was superior in P uptake and had an 8 fold higher number of pods. Genotypic variation in pod number was apparent before genotypic variation for P uptake was detected, which showed that pod number and P uptake are independent aspects of tolerance to P- deficiency. Wasedairyu was either able to efficiently translocate P to flowers and developing fruits or tolerated low P concentrations better than other genotypes. After day 85 daily uptake rates increased 4-fold in Kintoki and 12-fold in Wasedairyu but remained low in ICGV 87358. Because P uptake increased only after pod setting and because differences in root development failed to explain the observed changes in P uptake, we concluded that genotypic differences in P uptake were due to direct P uptake of fruiting organs. By having 16 pods, Wasedairyu was able to obtain a greater amount of P directly through fruiting organs than genotypes with only one or two pods. Gynophores (pegs) of Wasedairyu were furthermore characterized by being densely covered with root hair like outgrows that could have increased P uptake by increasing the surface area in contact with the soil. Hairs were detected in lesser number on pegs of Kintoki but ICGV 87358, as the genotype without an increase in P uptake rates during pod filling, completely lacked any hair development. These results suggest that genotypic variation for uptake of Fe–P exists and that direct P uptake through fruiting organs, as facilitated by the presence of root hair like outgrows on the pegs of some genotypes, contributes to this variation.