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Demystifying the endophytic and saprophytic ecology of Fusarium oxysporum f.sp lycopersci race 3 for improved Fusarium wilt management in tomato

Cassandra Swett: Department of Plant Pathology, University of California - Davis

<div>The life history strategies of pathogens in the <em>Fusarium oxysporum</em> species complex include abilities as non-pathogenic endophytes and saprophytes; these stages perpetuate persistence of soil-borne inoculum and enhance the risk of resistance-breaking race emergence. With recent geographic expansion of the Fusarium wilt pathogen of tomato, <em>Fusarium oxysporum </em>f. sp<em>. lycopersci</em> race 3 (Fol R3) within California, population management has become critical. We evaluated cryptic pathogen sources as contributors to Fol R3 population persistence and growth. Five Fol R3 isolates all systemically colonized a resistant tomato cultivar (20-80% incidence). Compared with susceptible cultivars, infection incidence in resistant cultivars was the same (100%), but extent of root and shoot colonization was 65% and 97% lower respectively. Fol R3 colonized diverse rotation crops; plant infection incidence in cantaloupe (Cucurbitaceae) and sunflower (Asteraceae) were the same as tomato but 20% lower in rice and corn (Poaceae). All rotation crops could be systemically colonized, but the extent of shoot colonization was 40-50% lower in Poaceae crops than tomato. Studies are underway to connect colonization extent with soil inoculum loads and wilt development. These studies reveal that resistant tomato cultivars, non-tomato rotation crops, and Fol R3 hosts may be high risk rotations, whereas certain grass crops may help manage soil inoculum loads.</div>