The Tripartite Interaction Between Arbuscular Mycorrhizal Fungi, Rice, and Insects

Losses caused by pests remain an important limitation to achieving high rice yields in the United States. Arbuscular mycorrhizal fungi (AM fungi) are able to modify plant physiology by increasing plant growth or inducing defense responses against insect herbivores. However, studies of the role of AM fungi in agroecological factors, including natural occurrence, plant resistance, soil dependency, and plant tolerance, with specific regards to pests that feed on rice plants have not been conducted before. A three-year study revealed natural occurring colonization by AM fungi on rice roots sampled in four rice-producing areas in the southern United States. Overall, rice-AM fungi associations were greatest in Arkansas followed by Mississippi, Texas, and then Louisiana. In the plant resistance study, larval performance and pathogen infection of different pests on rice cultivars inoculated with AM fungi in Louisiana were investigated. Results from this study revealed that densities of rice water weevil (RWW) larvae, weight gains of fall armyworm (FAW) larvae, and susceptibility to sheath blight infection were higher on rice plants treated with AM fungi inoculum. In the soil-dependent study, the susceptibility to RWW and FAW was increased in AM fungi-treated rice plants, but this effect was soil dependent. The enhanced effect on plant biomass was also soil dependent, but the inoculation of AM fungi had no effect on N or P concentrations nor on rice yields in both soil types. In the tolerance study, AM fungi seed treatment did not reduce RWW densities, but NipsIt INSIDE seed treatments reduced RWW densities. In addition, plant biomass and yields were higher in AM fungi-treated plants compared to untreated plants. This study provided strong support that the effects of AM fungi seed treatments can be more effective to increase rice biomass and yields. Taken together, findings from this work reveal that rice plants inoculated with AM fungi may provide an effective method for herbivore control (especially for the RWW) for increasing plant biomass and yields, but also highlight the complicated nature of the various factors governing rice-AM fungi-pest interactions. The broader implications of this study are important due to the potential impact that AM fungi may have on IPM and future research. Thus, gaining a better understanding of the underlying mechanisms of AM fungi on rice-pest interactions will contribute to the development of more effective and sustainable strategies to control or reduce pest damage in rice.