Genotypic variations in phosphorus accumulation in wild cowpea relatives ( Vigna vexillata ) grown under phosphorus deficiency

Vigna vexillata is a wild cowpea relative inhabiting tropical and subtropical regions. Because phosphorous (P) deficient soils are widely found in these regions, such wild relatives may have an ability to efficiently capture and utilize P in soils and thus can be potential materials of green manure to improve soil-plant nutrient cycles and subsequent crop production. Genotypic variations in shoot P content were evaluated in P-deficient (−P) and P-fertilized (+P) conditions of the pot experiment to clarify the ability of P accumulation in V. vexillata. Among the 14 accessions, five with a high shoot P content under P deficiency were identified. The high shoot P contents were attributed to large shoot biomass rather than high shoot P concentrations. The larger biomass of these accessions was consistent under the -P and +P conditions, indicating that potential growth characteristics without P restriction were a major driving factor of P accumulation even under P deficiency. In contrast, accessions with low shoot P content had small shoot biomass with high P concentrations. These accessions exhibited superior drought tolerance than those with large shoot biomass, presumably because of the small water consumption due to the small shoot biomass. The trade-offs between the shoot P accumulation and drought tolerance should be considered for genotype selection under the conditions where P deficiency and drought risks are often complex.