Organic farming sharpens plant defenses in the field

Authors: Krey, Karol; NABITY, PAUL - University Of California; BLUBAUGH, CARMEN - Clemson University; FU, ZHEN - Texas A&M University; VAN LEUVEN, JAMES - University Of Idaho; REGANOLD, JOHN - Washington State University; BERIM, ANNA - Washington State University; GANG, DAVID - Washington State University; JENSEN, ANDY - Washington State Potato Foundation; SNYDER, WILLIAM - University Of Georgia

Submitted to: Molecular Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2020
Publication Date: 7/17/2020
Citation: Krey, K.L., Nabity, P.D., Blubaugh, C.K., Fu, Z., Van Leuven, J.T., Reganold, J.P., Berim, A., Gang, D.R., Jensen, A.S., Snyder, W.E. 2020. Organic farming sharpens plant defenses in the field. Molecular Ecology. 97(4). https://doi.org/10.3389/fsufs.2020.00097.
DOI: https://doi.org/10.3389/fsufs.2020.00097

Interpretive Summary: Plants deploy a variety of defenses to protect themselves against herbivores and pathogens. Inputs (i.e. fertilizers, insecticides) often vary between organic versus conventional farms, reflecting the many differences in management practices between these farming systems. A researcher at USDA-ARS Wapato in Washington, in collaboration with scientists from Washington State University, University of Idaho, University of California, Clemson University, and University of Georgia, looked at plant gene expression in potato leaves in relation to insect damaged versus undamaged leaves and farm management. In one variety of potato, we found significantly heightened initiation of genes associated with plant-defense pathways in plants grown in organic versus conventional fields. Our results suggest that organic farming has the potential to increase plants’ resistance to herbivores. This adds information on the importance of farming management and crop variety and that some strategies have the potential to possibly facilitated a reduced need for insecticide applications.

Technical Abstract: Plants deploy a variety of chemical and physical defenses to protect themselves against herbivores and pathogens. Organic farming seeks to enhance these responses by improving soil quality, ultimately altering bottom up regulation of plant defenses. While laboratory studies suggest this approach is effective, it remains unclear whether organic agriculture encourages more-active plant defenses under real-world conditions. Working on the farms of cooperating growers, we examined gene expression in the leaves of two potato (Solanum tuberosum) varieties, grown on organic versus conventional farms. For one variety, Norkotah, we found significantly heightened initiation of genes associated with plant-defense pathways in plants grown in organic versus conventional fields. Organic Norkotah fields exhibited lower levels of nitrate in soil and of nitrogen in plant foliage, alongside differences in communities of soil bacteria, suggesting possible links between soil management and observed differences in plant defenses. Additionally, numbers of predatory and phloem-feeding insects were higher in organic than conventional fields. A second potato variety, Alturas, which is generally grown using fewer inputs and in poorer-quality soils, exhibited lower overall herbivore and predator numbers, few differences in soil ecology, and no differences in gene-activity in organic and conventional farming systems. Altogether, our results suggest that organic farming has the potential to increase plants’ resistance to herbivores, possibly facilitating reduced need for insecticide applications. These benefits appear to be mediated by plant variety and/or farming context.