Pathogenicity of Fusarium Xylarioides, the Causal Pathogen of Coffee Wilt Disease, in Coffee Seedlings and an Alternate Host, Tomato Fruit

Widespread crop cultivation has offered more opportunity for pathogens to evolve resulting in the emergence of new virulence and lifestyle patterns. Alternate hosts surrounding a crop field can also help pathogens survive, spread and provide inoculum for subsequent growing seasons. Examining pathogen hosts under laboratory conditions can explain disease emergence mechanisms. Here, we studied four strains of Fusarium xylarioides, a soil-borne, vascular fungal pathogen that causes coffee wilt disease collected over several decades and preserved in the CABI culture collection. We observed that these fungi can colonise tomato fruits as an alternate host to coffee and used these to test the pathogenicity of historic F. xylarioides and F. oxysporum f. sp. lycopersici strains. Expression of effector genes in F. xylarioides was compared in both the primary (coffee) and an alternate plant host (tomato). We used pathogenicity assays on coffee seedlings and tomato fruits by fungal staining, diagnostic end-point PCRs and real-time quantitative PCRs to verify the infection of both plant hosts. Passaging through coffee seedlings (infection followed by re-isolation of the pathogen) resulted in increased effector gene expression and enhanced pathogenicity. These findings indicate that alternate hosts may act as reservoirs for the pathogen, with implications for disease persistence and spread. A clearer understanding of plant disease cycles is therefore essential for the development of effective management strategies aimed at mitigating impacts on global food production.