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 vs. conventional farms. For one variety, Norkotah, we found significantly heightened initiation of genes associated with plant-defense pathways in plants grown in organic vs. 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.
Highlights
Conventional farming methods often largely rely on chemical insecticides for the control of herbivorous insects (e.g., Soffe, 2002; Stockdale et al, 2002; Klonsky, 2012)
For Norkotah, insect herbivory led to higher enrichment of defenserelated genes in transcripts of plants from organic systems compared to conventional, and had more upregulated genes related to plant stress (P = 0.01; Figure 1, stress perception; Table 1; Supplementary Table 6)
In Norkotah organic insect damaged leaves, genes associated with light harvesting and photosynthetic carbon assimilation strongly decreased (Figure 1, growth and development; Table 1; Supplementary Table 6), photosynthetic assimilation (PS) and nutrient transport related genes were more enriched in transcripts (PS, P < 0.001; Table 1; Supplementary Table 6, transport, P = 0.01; Table 1; Supplementary Table 6) and more PS genes were downregulated (P < 0.001; Table 1; Supplementary Table 6)
Summary
Conventional farming methods often largely rely on chemical insecticides for the control of herbivorous insects (e.g., Soffe, 2002; Stockdale et al, 2002; Klonsky, 2012). This approach can inadvertently disrupt biological control and worsen pest outbreaks when broad-acting chemicals kill natural enemies (Penman and Chapman, 1988; Prischmann et al, 2005; Woods et al, 2012). Neonicotinoid insecticides can suppress expression of important plant defense genes, alter levels of phytohormones involved in plant defense, and decrease plant resistance to herbivores such as spider mites (e.g., James and Price, 2002; Szczepaniec et al, 2013). Conventional modern agriculture can impact both top-down herbivore suppression, by harming natural enemies, and bottom-up herbivore suppression, by disrupting plant defenses
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call