Pathogenicity and Distribution along a Mediterranean-Subalpine Gradient.

species have been traditionally regarded as brackish water oomycetes; however, recent reports in inland freshwater call for a better understanding of their ecology and possible pathogenicity. We studied the distribution of in 117 forest streams by metabarcoding river filtrates taken in spring and autumn and by direct isolation from floating leaves. Pathogenicity on six species and was assessed by stem inoculations. The distribution of was correlated with high mean annual temperatures (>93.5% of reports in Ta > 12.2 °C) and low precipitation records. was therefore widely distributed in forest streams in a warm-dry climate, but it was mostly absent in subalpine streams. was primarily detected in autumn with few findings in spring (28.4% vs. 2.7% of streams). was able to cause small lesions on some tree species such as , and . Our findings suggest that may be adapted to warm and dry conditions, and that it does not pose a significant threat to the most common Mediterranean broadleaved trees.