Phytophthora Fragariae - Disease Cycle

Disease Cycle

P. fragariae survives in the soil in the form of oospores. These oospores can survive for up to 4 years; there are some reports of spores remaining viable 13 – 15 years. The oospores germinate to form usually one sporangia. Sporangia germinate in the presence of water to release motile zoospores. The presence of water is important because the zoospores have no way to reach a host without swimming. The zoospores swim through the water in the soil to find roots where they encyst and form germination tubes to infect the plant. This usually occurs in the late autumn or early spring. Growth of the disease occurs mostly in the stem and root. Hyphae protrude out of the root and produce new, secondary sporangia. The secondary sporangia are usually produced in winter months and the process takes a few days. The sporangia are produced more quickly in cold temperatures. The new sporangia move through water in the soil to infect new plants.

The infection can be spread from field to field by unsantized tools or equipment, floodwater, or any other activity that will move infected soil. Also, the replanting of infected nursery stock will spread the infection of P. fragariae.