Effects of Soil Water Potential and Diurnal Temperature Fluctuation on Survival of Soilborne Phytophthora ramorum and Phytophthora Pini Inoculum.

Solarization has been used in various agricultural systems to manage soilborne plant pathogens. Research on solarization efficacy has focused on the minimum temperature and exposure time required to inactivate soilborne pathogens. Most mathematical models of soil solarization assume a cumulative temperature effect over time. Few studies have addressed how soil water matric potential and diurnal temperature fluctuation may influence solarization effects on soilborne pathogens. To develop a more accurate predictive model for soil solarization effectiveness, we conducted controlled lab experiments with Phytophthora ramorum and P. pini. Leaf disks infested with each pathogen were incubated at water potentials of 0, -0.1, -1.0, and -10 MPa simulated with different polyethylene glycol concentrations, and were exposed to constant temperatures (35°C, 38°C, and 50°C). For both pathogens, survival frequency was greater at lower water potentials. Survival was also greater when inoculum was subjected to intermittent rather than constant heat, suggesting that the temperature effect is not cumulative. Growth chamber experiments designed to simulate a diurnal temperature pattern resulted in pathogen survival frequency similar to what occurred in solarization field trial. A mathematical model was developed from lab experiments and field trials to predict the minimum solarization period required to kill P. ramorum and P. pini. Soil water potential and temperature fluctuation are important factors that influence the effectiveness of soil solarization for management of Phytophthora spp.