Pierce’s Disease is caused by the bacterium Xylella fastidiosa (Xf), which targets the xylem of grapevines, impeding the flow of nutrients and water throughout the plant, and ultimately leading to its death. The observation that certain vines escaped infection, despite being genetically identical to nearby dying vines, led us to hypothesize that natural products produced by endophytic fungi were protecting these ‘disease-escaped’ vines from Xf. With this hypothesis, we isolated fungi from both sick and disease-escaped grapevines and identified the natural product radicinin from Cochliobolus sp. as an inhibitor of Xf. In an effort to optimize production of radicinin for greenhouse studies, we obtained four commercially available radicinin-producing strains of fungi: Alternaria helianthi, A. radicina 58405, A. radicina 96831, and Curvularia lunata. These radicinin-producing strains were grown in several different media over 42 days, and radicinin was quantified in the culture broth using HPLC to determine the optimal fermentation conditions. Shaken cultures of A. radicina 96831and C. lunata in potato dextrose broth produced the most radicinin, at concentrations of 570 mg/mL and 360 mg/mL, respectively. We also prepared whole culture broth of these high radicinin-producing strains for testing in planta. Given that these strains are plant pathogenic, we developed a protocol to heat-kill the fungi – while still retaining radicinin – for testing the whole culture broth as a microbial biopesticide against Xf; a classification regulated by the Environmental Protection Agency (EPA).

Isolation and formulation of radicinin as a microbial biopesticide against Pierce’s Disease

2019 Spring National Meeting

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