Promoting Growth Performances and Phytochemicals of Black Upland Rice Through the Co-Inoculation of Arbuscular Mycorrhizal Fungi and Endophytic Fungi Under Drought Conditions

Drought is a major problem affecting upland rice growth worldwide, including in northeast Thailand, with insufficient irrigation, where drought stress leads to reduced yields and may affect the functional compound content of rice grains. This research aimed to study the efficacy of arbuscular mycorrhizal fungi (AMF) <i>Rhizophagus variabilis</i> KS-02 and endophytic fungi (EPF) <i>Trichoderma zelobreve</i> PBMP16 on promoting the growth and accumulation of functional substances in upland black rice under drought conditions. Factorial experiments in a randomized complete block design (RCBD) were conducted by cultivating rice inoculated with AMF and EPF as well as co-inoculated with AMF+EPF under three watering conditions: 100% field capacity (FC), 66% FC, and 33% FC. The results show that both AMF, EPF improved some plant growth parameters and physiological performance under both well-watered and water-limited conditions. Inoculating plants with fungi increased the production of enzymes APX, CAT, and GR, as well as proline, which helps plants tolerate water deficit stress. Functional grain quality, including phenolic compounds, anthocyanins, and antioxidant activity, was also increased by fungal inoculation. While co-inoculation provided advantages for certain parameters, particularly antioxidant activity and biomass, single inoculation with AMF or EPF was equally effective or superior for specific traits depending on the level of water stress. Overall, this report shows that both AMF and EPF contribute to improving the productivity and functional quality of upland black rice under drought conditions, with treatment effects varying according to fungal type and water availability.