Patterns and Distribution of Botryosphaeriaceae Fungi Related to Dieback in Big Berry Manzanita.

Dieback and mortality in wildland plant species due to climate change have been on the rise in recent decades, and latent fungal pathogens might play a significant role in these events. During a severe multiyear drought, canopy dieback associated with latent pathogens in the Botryosphaeriaceae () family was observed in stands of a dominant shrub species, big berry manzanita (), across chaparral landscapes in California. These fungi are significant pathogens of woody agricultural species, especially in hosts experiencing stress, and have become a threat to economically important crops worldwide. However, little is known regarding their occurrence, distribution, and impact in wildland systems. We conducted a field survey of 300 shrubs across an elevational gradient to identify species infection as it relates to (i) dieback severity and (ii) landscape variables associated with plant drought stress. Our results show that are widely infecting across the landscape, and there is a significant correlation between elevation and dieback severity. Dieback severity was significantly higher at lower elevations, suggesting that infected shrubs at lower elevations are at greater risk than those at higher elevations. Furthermore, two species, and , were most frequently isolated, with being the most common and, based on haplotype analysis, likely the most recently introduced of the two. Our results confirm the wide distribution of latent fungi in a wild shrubland system and provide valuable insight into areas of greatest risk for future shrub dieback and mortalit. These findings could be particularly useful for informing future wildlands management strategies with regard to introduced latent pathogens.