Early Detection of Fungal Plant Pathogen Invasions in Natural Ecosystems Based on Bridge-Head Effect with the Emphasis on Phytophthora Species

Understanding the way of introduction and establishment of plant pathogens is essential to prevent new invasions. Most studies carried out in the last decade indicate that biological invasions are the result of the bridge-head effect. In other words, pathogens use a new environment or a new host plant as a primary base from which they can invade and cause epidemics in a proper time. Bridge-head effect has been observed with plant pathogens such as bacteria, fungi, and oomycetes in urban trees. Urban landscapes are usually the first point of contact of exotic novel pathogens with endemic plants, which is often due to the concentration of human activities and the introduction of exotic plants in these areas. Urban trees are a suitable location for the establishment of invasive pathogens which have been accidentally arrived at the area. Bridge-head effect probably plays a significant role in causing long-term damages and cause costly attempts for the management of plant pathogens. In contrast, for early detection of novel or invasive pathogens, one may use urban trees as sentinel plantings and the damages caused by these pathogens could be managed by prediction of the disease occurrence. There are some evidences for the existence of the bridge-head effect for oomycetes in urban trees and ornamental plants in Iran. Moreover, there are some reports indicating the existence of novel pathogens in these areas. The aim of this article is to review the aspects of the bridge-head effect in plant fungal and oomycete pathogens as well as planning to manage the potential threat to Iran’s natural ecosystems caused by their bridge-head effects.