In Madagascar, upland rice cropping is constrained by soil acidity and low phosphorus (P) bioavailability. Given their role in plant P nutrition, arbuscular mycorrhizal fungi (AMF) may improve crop yield in nutrient-poor tropical soils. In the Vakinankaratra region, a field experiment was conducted at 908 m asl on an acidic Ferralsol during the 2019–2020 growing season. The aim was to test the ability of four promoted rice varieties to respond to AMF seed-coating inoculation with a commercial strain of Rhizophagus irregularis in the absence or presence of P fertilizer (20 kg ha-1 of P2O5) under no expected nitrogen (N) limitation. In absence of P fertilization, both at tillering and at maturity and irrespective of the rice varieties, AMF inoculation significantly improved plant performance and finally grain yield, grain N, and grain P amounts by an average of 28%, 30%, and 39%, respectively. In contrast, when P fertilizer was supplied, no significant effect of AMF inoculation was observed. Rice growth variables were significantly higher with the application of P fertilizer than with AMF inoculation both at tillering and at maturity. P fertilizer without inoculation provided an average grain yield improvement of 85%. At tillering, mycorrhizal parameters for root colonization assessment were not positively linked with rice growth variables suggesting an early effect of AMF inoculation. We concluded that, with no P fertilization, AMF seed coating inoculation at the field scale significantly improved upland rice plant performance in a limited soil P environment. Our rice genetic variability did not interfere significantly both with mycorrhizal parameters and crop AMF inoculation benefits.