Associate Professor Washington State University Pullman, Washington
Several insect species transmit pathogens to plants through feeding. Bacteria, viruses, and phytoplasmas can have significant consequences in both agricultural and conservation contexts, reducing yields and threatening native species. Today, insecticides are the dominant solution to address these problems, but carry environmental costs and strong public scrutiny. With that in mind, it is prudent to identify potential alternatives to foliar insecticide use. This review examines how two common soil amendments – arbuscular mycorrhizal fungi (AMF) and brassicaceous biofumigants – alter plant immunity to insect-vectored pathogens. Many farmers rent land and may not have access to the fields in the off years to be able to make long-term adjustments, such as multi-year crop rotations. These amendments were selected because they can be implemented in a single year, within the confines of a conventional farming system. Various AMF species exist naturally in the soil and form relationships with 80% of terrestrial plants. While AMF has been studied widely as a method to increase crop yields and reduce soil-borne pathogens less is known about their role in aboveground disease susceptibility. Similarly, brassicaceous biofumigants are applied as a seed meal or grown as a cover crop the fall before the cash crop. Biofumigants are presented as an opportunity to eliminate traditional soil fumigants; however, it is unclear how these products ultimately affect plant disease. Better understanding the role of soil in plant-pathogen interactions could have immediate implications for farmers and conservationists, potentially reducing the need for unpopular and sometimes unsafe insecticides.
