Legume-derived phenolic acids influence Fusarium oxysporum f.sp. strigae compatibility and biocontrol potential in a Striga push–pull system

Abstract

Biological control of Striga hermonthica (Del.) Benth. includes push–pull, intercropping using legumes, and soil-borne fungi such as Fusarium oxysporum f.sp. strigae (FOS). Efficacy of both technologies is compromised by various environmental factors. Combining them could potentially overcome their limitations and enhance control of S. hermonthica. It was hypothesized that FOS inoculation is compatible with push–pull intercropping, allowing consistent S. hermonthica suppression. Effects of selected phenolic acids and crude root exudates from three legume species (Mucuna pruriens, Desmodium uncinatum, Crotalaria juncea) on FOS mycelial growth and spore germination were studied. Bioassays showed that most phenolic acids (e.g., caffeic, p-hydroxybenzoic, syringic) had no effect on FOS development, except for piperonylic (80 %, 38 %) and t-cinnamic (53 %, 33 %) acids, which strongly inhibited growth at concentrations of 1 and 0.5 mM, respectively. Crude root exudates from Crotalaria inhibited FOS mycelial growth at 1 (44 %) and 0.5 (32 %) mg ml^-1. Desmodium and Mucuna exudates showed no inhibition. Greenhouse results showed that legume intercropping and FOS inoculation reduced S. hermonthica emergence, with their integration achieving over 95 % suppression and boosting maize biomass. Legume presence enhanced FOS proliferation, with Mucuna and Desmodium increasing FOS gene copy numbers by over 44 %. LC-MS analysis identified nine phenolic acids, with p-coumaric (85–128 µg g⁻¹) and p-hydroxybenzoic (50–97 µg g⁻¹) acid being most abundant; the latter positively correlated with FOS abundance. In this setting, legume intercropping with maize did not impair FOS proliferation in rhizosphere soil and effectively suppressed S. hermonthica, demonstrating compatibility of FOS inoculation with push–pull for effective S. hermonthica management.