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

Lina Bernaola,Michael J Stout

doi:10.1007/s10340-020-01279-7

Lina Bernaola, Michael J Stout

Open Access

https://doi.org/10.1007/s10340-020-01279-7

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Abstract

Associations 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.

Highlights

The below-ground herbivores, pathogens, and microbial symbionts associated with the roots of a plant can affect organisms inhabiting above-ground portions of the plant and vice versa (Soler et al 2012), and these interactions may affect the yield or fitness of plants
In Exp-1, -2, and -4, arbuscular mycorrhizal (AM) fungi root colonization was significantly lower in the +AMF + NsI treatment than in the AMF-only (+AMF −NsI) treatment; this was reflected by a significant effect of NipsIt seed treatment in Exp-1, a marginally significant effect in Exp-4, and a significant AM fungi x NipsIt interaction in Exp-1, -2, and -4 (Table 1; Fig. 1B)
Inoculation of soil with AM fungi has been suggested as a sustainable approach to overcome reductions in crop yields caused by insect pests by altering the physiological and biochemical properties of the crop plant (Bennett et al 2006; Wang et al 2015)

Summary

Introduction

The below-ground herbivores, pathogens, and microbial symbionts associated with the roots of a plant can affect organisms inhabiting above-ground portions of the plant and vice versa (Soler et al 2012), and these interactions may affect the yield or fitness of plants. Associations with soil microorganisms may affect the ability of a plant to recover from herbivore injury. The ability of crop plants to sustain yields under herbivore attack is critical for sustainable crop production. 2001) and form obligate mutualistic associations with the roots of many plants, including many crops (Smith and Read 2008). Herbivores affect plants by removing biomass and reducing photosynthetic area (Agrawal et al 2012). Both AM fungi and insect herbivores interact in complex and multifaceted ways with their host plants and can interact with each other via changes they induce in their shared host plant (Gehring and Bennett 2009)

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