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Reduced insect pest populations found on long-term organic farms have mostly been attributed to increased biodiversity and abundance of beneficial predators, as well as to changes in plant nutrient content. However, the role of plant resistance has largely been ignored. Here, we determine whether host plant resistance mediates decreased pest populations in organic systems and identify potential underpinning mechanisms. We demonstrate that fewer numbers of leafhoppers (Circulifer tenellus) settle on tomatoes (Solanum lycopersicum) grown using organic management as compared to conventional. We present multiple lines of evidence, including rhizosphere soil microbiome sequencing, chemical analysis and transgenic approaches, to demonstrate that changes in leafhopper settling between organically and conventionally grown tomatoes are dependent on salicylic acid accumulation in plants and mediated by rhizosphere microbial communities. These results suggest that organically managed soils and microbial communities may play an unappreciated role in reducing plant attractiveness to pests by increasing plant resistance.

Heightened interest in biologically-based methods of raising crop yields has driven research into beneficial microorganisms that can be used to improve crop growth and productivity. This review addresses the potential of rhizobia, vesicular-arbuscular mycorrhizae (VAM), and plant-growth-promoting rhizobacteria to improve growth of soybean (Glycine max (L.) Merr) under temperate conditions. Mechanisms of action of beneficial microorganisms and considerations for utilization at all root-zone temperatures (RZTs) are reviewed. Subsequent sections address current knowledge on the inhibition of soybean growth at low RZTs and the potential of beneficial microorganisms to alleviate low temperature stress. The three categories of beneficial microorganisms discussed differ in their modes of action and have shown potential for additive or synergistic growth promotion of soybean at all RZTs. At low RZT, pot and field studies have identified strains of rhizobia and PGPR, as well as certain phytohormones, that ameliorate the inhibitory effects of cold stress on soybean growth through a variety of mechanisms. Wider use of these treatments could aid the expansion of soybean cultivation in cold climates.