Abstract:
Emerging diseases caused by both native and exotic pathogens represent
a main threat to forest ecosystems worldwide. The two invasive soilborne
pathogens Phytophthora cinnamomi and Phytophthora cambivora are the
causal agents of ink disease, which has been threatening Castanea sativa
in Europe for several centuries and seems to be re-emerging in recent
years. Here, we investigated the distribution, causal agents, and infection
dynamics of ink disease in southern Switzerland. A total of 25 outbreaks
were identified, 19 with only P. cinnamomi, 5 with only P. cambivora, and
1 with both species. Dendrochronological analyses showed that the disease
emerged in the last 20–30 years. Infected trees either died rapidly within
5–15 years post-infection or showed a prolonged state of general decline
until death. Based on a generalized linear model, the local risk of occurrence
of ink disease was increased by an S-SE aspect of the chestnut
stand, the presence of a pure chestnut stand, management activities, the
proximity of roads and buildings, and increasing annual mean temperature
and precipitation. The genetic structure of the local P. cinnamomi population
suggests independent introductions and local spread of the pathogen.
