The effect of mycorrhizal seed treatments on rice growth, yield, and tolerance to insect herbivores

Abstract

AbstractAssociations with arbuscular mycorrhizal (AM) fungi can increase or decrease plant resistance to herbivory in different crop systems, but the effects of AM fungi on plant tolerance to pests remain largely unknown. We investigated whether inoculation of rice (Oryza sativa) with AM fungi stimulates plant growth, yield, and/or tolerance to rice water weevil (Lissorhoptrus oryzophilus) injury. Rice plants were exposed to natural infestations of herbivores during early and mid-to-late season over four field experiments. The experiments followed a 2 × 2 factorial design consisting of two AM fungi seed treatments (inoculated or non-inoculated with AM fungi) and two insecticide seed treatments (treated or untreated). Inoculation with AM fungi increased root colonization in all four field experiments in rice. Inoculation with AM fungi increased densities of weevil larvae and whiteheads resulting from stemborer infestations, while insecticidal seed treatments significantly reduced densities of weevils and marginally reduced whiteheads. Inoculation with AM fungi increased rice biomass before and after flooding, and a clear but not always significant increase in yield was observed in plants inoculated with AM fungi. However, inoculation with AM fungi did not reduce percent yield losses after herbivory injury. Analyses of nutrient contents in roots and shoots revealed inconsistent effects of inoculation with AM fungi. This study highlights for the first time the potential for AM fungi seed treatments to increase rice tolerance to insect pests by influencing plant biomass and yields.