Test of plant defense elicitors for arthropod pest suppression and PR-1 gene induction in pear orchards

Authors: ORPET, ROBERT J - Washington State University; Cooper, William - Rodney; BEERS, ELIZABETH - Washington State University; NOTTINGHAM, LOUIS - Washington State University

Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2021
Publication Date: 9/30/2021
Citation: Orpet, R., Cooper, W.R., Beers, E.H., Nottingham, L.B. 2021. Test of plant defense elicitors for arthropod pest suppression and PR-1 gene induction in pear orchards. Entomologia Experimentalis et Applicata. 169(12):1137-1146. https://doi.org/10.1111/eea.13110.
DOI: https://doi.org/10.1111/eea.13110

Interpretive Summary: Plant defense elicitors are treatments that activate plant defenses providing the plants with protection against plant pathogens and insect pests. Treatment of pear trees with the defense elicitors ASM and harpin protein was previously shown to suppress populations of pear psylla under experimental conditions, but it was not yet clear whether these defense elicitors are effective against pear psylla in orchards that are commercially managed. Researchers at the Washington State University in Wenatchee, WA and USDA-ARS in Wapato, WA found that single applications of defense elicitors in commercially managed orchards did not induce strong enough defense responses to suppress pear psylla populations beyond the control provided by other insecticide applications and pest management practices. By comparing the expression of defense-related genes in treated and untreated pear trees, they confirmed that application of defense elicitors activates plant defenses under experimental conditions but had little effect on trees in commercially-managed orchards. These results show that defense elicitors may provide inconsistent control of pear psylla in commercial orchards

Technical Abstract: Plant defense elicitors (PDEs) are chemicals that stimulate plant defenses against pathogens and herbivores. Previous work shows that PDEs acibenzolar-S-methyl (ASM) and harpinaß protein (harpin) can induce the pathogenesis gene PR-1 in plants and suppress herbivorous arthropods. In this study, we tested the potential for these PDEs to induce PR-1 in pear (Pyrus communis L; Roscaceae) orchards and suppress pear psylla (Cacopsylla pyricola [Förster]; Hemiptera:Psyllidae) and spider mites (Tetranychus; Acari: Tetranychidae). In 2017 and 2018, we compared densities of each pest on mature pear trees following a single application of either an ASM product (Actigard), a harpin product (Employ), or no PDE treatment in four commercial and two research orchards. In 2018, we collected pear leaf samples from field plots before and after PDE treatments for qPCR to assess PR-1 induction. Neither PDE treatment showed evidence of pest suppression in either year, and no differences in PR-1 expression were detected. Potted greenhouse trees treated with ASM in 2019 showed higher PR-1 expression relative to untreated trees, verifying the ability of our procedures to detect induction and suggesting that a single PDE application was sufficient to induce PR-1 in potted but not mature pear trees. Taken together with findings of previous studies, we conclude that plant defense elicitors may contribute to pear pest suppression in some contexts, but effects are unlikely to be strong or consistent. Overall, our results highlight the need for field experiments to advance plant defense elicitor knowledge towards effective field applications