MORPHO-PHYSIOLOGICAL DROUGHT TOLERANCE RESPONSE OF UPLAND RICE VARIETIES (Oryza sativa L.) TO ARBUSCULAR MYCORRHIZAL FUNGI INOCULATION UNDER MOISTURE STRESS AT DIFFERENT GROWTH STAGES

Abstract

Drought stress is a major constraint on upland rice production in sub-Saharan Africa. Arbuscular mycorrhizal fungi (AMF) are a natural and sustainable means of enhancing drought tolerance. This study investigated morphological and physiological drought tolerance responses of three upland rice varieties (NERICA-1, NERICA-4, and Ofada) inoculated with three AMF species (Funneliformis mosseae (Fm), Rhizophagus irregularis (Ri), Glomus etunicatum (Ge), and no AMF under moisture stress imposed at three growth stages (vegetative, reproductive, grain filling and no moisture stress) in a screenhouse. A 3×4×4 factorial completely randomized design with three replications was used. Inoculation with Glomus etunicatum under reproductive-stage stress produced the largest leaf area at 8 WAT. Funneliformis mosseae significantly enhanced N, P, and K uptake in Ofada and increased the grain yield of NERICA-1. AMF root colonization (arbuscules, vesicles, hyphae) was significantly higher in Glomus etunicatum-inoculated plants across all moisture regimes. Moisture stress at the reproductive stage produced the greatest yield reductions, whereas Ge and Fm inoculation significantly mitigated stress effects.  There were strong positive associations among AMF colonization percentage, root volume, shoot biomass, and grain yield. There are differential roles of AMF species in modulating drought tolerance at specific growth stages. Glomus etunicatum and Funneliformis mosseae are identified as superior inoculants for improving drought resilience in upland rice in southwestern Nigeria.