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

Abstract

Dieback and mortality in wildland plant species due to climate change has been on the rise in recent decades, and latent fungal pathogens may play a significant role in these events. During a severe multi-year drought, canopy dieback associated with latent pathogens in the Botryosphaeriaceae (Bot) family was observed in stands of a dominant shrub species, big berry manzanita (Arctostaphylos glauca), 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 A. glauca shrubs across an elevational gradient to identify Bot species infection as it relates to a) A. glauca dieback severity and b) landscape variables associated with plant drought stress. Our results show Bots widely infecting A. glauca 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 Bot species, Neofusicoccum australe and Botryosphaeria dothidea, were most frequently isolated with N. australe 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 Bot fungi in a wild shrubland system, and provide valuable insight into areas of greatest risk for future shrub dieback and mortality.