Effect of electrical conductivity on survival of Phytophthora alni, P. kernoviae and P. ramorum in a simulated aquatic environment

This study investigated survival of the pathogens Phytophthora ramorum, P. alni and P. kernoviae as zoospores or sporangia in response to an important water quality parameter, electrical conductivity (EC), at its range in irrigation water reservoirs and irrigated cropping systems. Experiments with different strengths of Hoaglands solution showed that all three pathogens survived at a broad range of EC levels for at least 3 days and were stimulated to grow and sporulate at ECs > 1.89 dS m-1. Recovery of initial populations after a 14-day exposure was over 20% for P. alni subsp. alni and P. kernoviae, and 61.3% and 130% for zoospores and sporangia of P. ramorum, respectively. Zoospore survival of these pathogens at ECs < 0.41 dS m-1 was poor, barely beyond 3 days in pure water; only 0.3% (P. alni), 2.9% (P. kernoviae) and 15.1% (P. ramorum) of the initial population survived after 14 days at EC = 0.21 dS m-1. The variation in rates of survival at different EC levels suggests that these pathogens survive better in cropping systems than in irrigation water. Containment of run-off and reduction in EC levels may therefore be non-chemical control options to reduce the risk of pathogen spread through natural waterways and irrigation systems.