Arbuscular Mycorrhizal Fungi Inoculation and Water Regime Effects on Seedling P Uptake by Rice and Pearl Millet

Abstract

Mycorrhizal-mediated seedling establishment may reduce dependency on chemical fertilizers, but the effectiveness of infection for growth may differ depending on species with different eco-physiological adaptations. The infection of arbuscular mycorrhizal fungi (AMF) and P uptake were compared between rice (Oryza sativa L.) (Koshihikari (ricek), Togo4 (ricet)), and pearl millet (Pennisetum glaucum (L.) R. Br.) (ICMB89111 (millet891), ICMB95444 (millet954)) seedlings (i) in response to three different commercial AMF inoculants of Rhizoglomus irregulare (popular inoculant Dr. Kinkon (I1); two new inoculants Rootella P (I2) and Rootella F (I3)) in comparison with indigenous AMF from Andosol upland and paddy topsoils (Exp. 1–2 as the inoculant experiments) and (ii) across different water regimes from upland to flooded lowland conditions for I1 inoculant (Exp. 3–4 as the water regime experiments). The new inoculants I2 and I3 with higher propagule numbers showed a higher infection rate than the control seedlings in both rice and pearl millet, with a tendency for slower leaf development and no seedling growth enhancement. I1 inoculant had more significant positive effects on the root transversal area and shoot growth parameters than the control. The infection rates of all three inoculants were lower than the indigenous AMF from upland Andosol in rice and pearl millet, in which a higher infection rate led to higher P uptake found in millet954. I1 inoculant increased the infection rate in pearl millet and rice but had no clear indication of interaction with water regimes. A higher infection rate led to higher P uptake and shoot dry weight in pearl millet but not in rice with higher root length density. This study provided the significance of inoculants for seedling establishment and highlighted more mycorrhizal-mediated P uptake in pearl millet than in rice.