Aerial dispersal of Fusarium oxysporum f.sp. fragariae: A missing link in the disease cycle?

Fusarium oxysporum (Fo) is a major soilborne pathogen across many cropping systems. Our recent work in the Fusarium wilt of strawberry pathosystem suggests that aerial dispersal of spores from above-ground plant parts is epidemiologically important and an underappreciated aspect of Fo biology. Using cyclonic spore traps placed an infested strawberry field, we detected Fusarium oxysporum f.sp. fragariae (Fof) in aerial samples from strawberry fields in the Salinas Valley of California across three months. In laboratory tests, spores dislodged by simulated wind from sporulating plant material were observed to infest soils with no history of wilt. Soil that had been recently autoclaved or fumigated developed much greater levels of inoculum than non-sanitized soils. When foliar tissue of strawberries was inoculated with a spore suspension of Fof, wounded, but otherwise healthy, leaves were observed to develop lesions over several weeks, eventually becoming completely necrotic. Fusarium wilt symptoms were observed on several inoculated strawberry plants, and Fof was later recovered from the plant crown tissue using selective culturing protocols, seemly indicating a systemic infection. Our results will be broadly useful to researchers and pathology practitioners across cropping systems that struggle with this difficult to manage disease. Our results represent an advance in the understanding of Fo biology and the Fusarium wilt disease cycle, helping to explain previous management failures and providing new opportunities for disease management.