Interactions of Bambara groundnut ( <i>Vigna subterranean</i> (L) Verdc) genotypes and phosphorus fertilizer rates in controlling <i>Alectra vogelii</i>

Bambara groundnuts (Vigna subterranea (L.) Verdc) provide essential proteins for African farmers, but the yield is largely affected by Alectra vogelii infestation, particularly on nutrient-depleted soils. Laboratory and field investigations were conducted to assess the influence of phosphorus rates and Bambara groundnut genotypes on Alectra vogelii infestation. In the laboratory, a 4 × 26 factorial experiment, varying phosphorus rates (0, 20, 30 and 40 kg ha−1) across 26 genotypes, revealed a significant (p < 0.001) interaction affecting Alectra germination and furthest germination distance. Notably, at 40 kg P ha−1, Alectra seed germination and furthest distance were significantly reduced. In field studies, increasing phosphorus rates decreased Alectra shoot biomass and haustorial root attachments, except for a few resistant genotypes. Alectra counts at 109 days and grain yield demonstrated a significant (p < 0.001) interaction between Bambara genotypes and Alectra. Genotypes G15, G18, G20, and G25 exhibited no haustorial root attachments, with G18 achieving the highest grain yield per plant (23.41 g) under 0 kg P ha−1 on Alectra-infested soil. The synergy of Alectra-resistant genotypes with 40 kg P ha−1 proved to enhance the establishment and grain yield of Bambara groundnut.