Effects of arbuscular mycorrhizal fungi inoculation on infection and growth of rice and pearl millet in upland fields with three water regimes

Inoculation with arbuscular mycorrhizal fungi (AMF) may enhance crop growth in upland fields, depending on the water regime. To quantify changes in AMF infection rate and subsequent effects on nutrient uptake and growth, we grew rice (wetland crop) and pearl millet (dryland crop) genotypes with or without the commercial inoculant Dr. Kinkon (Glomus sp. R10) in Andosol upland fields in 2020 and 2021. Root infection rates were measured in shallow (0–10 cm) and deep (20–30 cm) layers under three water regimes: well-irrigated, half-irrigated, and non-irrigated. Inoculation enhanced shoot dry weight (SDW), plant height, tiller number, phosphorus (P) uptake, leaf water potential, photosynthetic rate (measured only in 2021) and root transversal area. The increase in SDW with inoculation was higher under well-irrigated than under water-limited conditions. The increment in pearl millet SDW was related to higher P uptake associated with higher infection rates, whereas that in rice SDW was related to maintenance of leaf water potential, greater root transversal area and root length density, and higher P uptake but not to infection rate parameters. Inoculation increased mycorrhizal and vesicular infection rates with the similar tendency for arbuscular infection rate and qPCR. Infection rates were similar across water regimes in both years despite significant differences in plant growth parameters with higher rates in deep than shallow layers. AMF inoculation enhanced infection rates, mostly independent of water regime, but plant growth enhancement was greater under the well-irrigated treatment and was more directly linked with infection rates in pearl millet.