Persistence of Fusarium oxysporum f. sp. fragariae in soil through asymptomatic colonization of rotation crops

Asymptomatic plant colonization is hypothesized to enhance persistence of pathogenic forms of Fusarium oxysporum in the absence of a susceptible host. However, a correlation between pathogen populations on living plant tissues and soilborne populations after tillage has not been demonstrated. Living and dead tissues of broccoli, lettuce, spinach, wheat, cilantro, raspberry, and strawberry plants inoculated with Fusarium oxysporum f. sp. fragariae (the cause of Fusarium wilt of strawberry) were assayed to quantify the incidence of infection and extent of colonization by this pathogen. All crops could be infected by F. oxysporum f. sp. fragariae, but the extent of colonization varied between plant species. Pathogen population densities on non-living crown tissues incorporated into the soil matrix were typically greater than those observed on living tissues. Crop-dependent differences in the inoculum density of F. oxysporum f. sp. fragariae in soil were only observed after decomposition of crop residue. Forty-four weeks after plants were incorporated into the soil, F. oxysporum f. sp. fragariae soil population densities were positively correlated with population densities on plant tissue fragments recovered at the same timepoint. Results indicate that asymptomatic colonization can have a significant, long-term impact on soilborne populations of Fusarium wilt pathogens. Cultural practices, such as crop rotation, should be leveraged to favor pathogen population decline by planting hosts that do not support extensive population growth on living or decomposing tissues.