Seasonal Dynamics of Foliar Fungi Associated with the Invasive Plant Ageratina adenophora

The potential of invasive plants to serve as reservoirs for plant pathogenic fungi has been confirmed, but studies examining the seasonal effects on the community structure and transmission patterns of leaf pathogens within invasive plant populations remain scarce. In this study, we characterised the seasonal dynamics of pathogenic fungal communities in the leaf tissue of the invasive plant A. adenophora via culture-dependent and culture-independent methods. The study confirmed that fresh leaves of A. adenophora accumulate diverse pathogenic fungi, including Colletotrichum, Epicoccum, Toxicocladosporium, Mycosphaerella and Didymella. These genera are globally distributed and act as pathogens for a wide range of wild plants and economic crops. The pathogenic fungal communities exhibited seasonal dynamics, though the magnitude of change was less pronounced than that of the overall fungal community. Among four common environmental factors, namely, temperature, relative humidity, wind speed and precipitation, temperature had a greater effect on the overall community than the other environmental factors, whereas precipitation had the least effect. However, relative humidity has the strongest effect on the pathogenic fungal community; moreover, relative humidity distinctively affects the same species occurring in different microenvironments. Most foliar pathogenic fungi are actively transmitted in spring and autumn, and very few genera can transmit across all seasons. Moreover, most fungal genera can transmit from fresh leaves to dead leaves, suggesting that most foliar fungal pathogens associated with A. adenophora are likely necrotrophic. Our study strongly confirms the potential of the invasive plant A. adenophora to act as a reservoir of pathogenic fungi and provides preliminary insights into their potential transmission patterns. These findings underscore that, under suitable climatic and environmental conditions, A. adenophora may pose a latent risk of triggering disease transmission within ecosystems.