APS Abstract of Presentation

Epidemiology of Phytophthora capsici in water
L. L. GRANKE (1), M. Hausbeck (1)
(1) Michigan State University, Plant Pathology
Phytopathology 98:S61

Phytophthora capsici has been detected in surface water used for irrigation in Michigan, but the epidemiology of P. capsici in water has not been elucidated. Controlled laboratory studies were undertaken to determine the effects of water temperature (1.5 ± 0.9, 12.4 ± 0.6, 19.4 ± 0.8, 22.4 ± 0.8, and 31.6 ± 0.7°C), zoospore concentration (100, 1,000, 5,000, 10,000, 20,000, and 40,000 zoospores/ml), and zoospore suspension age on Phytophthora capsici infection of cucumber fruit. For each temperature/concentration combination, six unwounded pickling cucumbers were added to 3 liters of zoospore suspension, removed 24 hours later, rinsed with distilled water, incubated in a moist chamber, and cucumber tissue was excised and plated onto field isolation media. Six unwounded pickling cucumbers were added to 3 liters of zoospore suspension immediately, 1 day, 3 days, or 5 days after zoospore suspension preparation to measure zoospore longevity at 19.4 ± 0.8°C. Cucumbers were removed 24 hours later and treated as described above. Three independent experiments were conducted for each temperature, concentration, and age tested. All experiments contained a negative control (0 zoospores/ml, 19.4 ± 0.8°C). No control fruit were infected. Fruit were not infected at 1.5 ± 0.9°C, but a high percentage of infection occurred at all other temperatures tested. The percent of fruit infected at concentrations greater than or equal to 1,000 zoospores/ml was significantly higher than the control. Concentrations greater than or equal to 5,000 zoospores/ml caused a significantly higher percentage of infection than 100 zoospores/ml. The ability of zoospores to infect cucumbers was significantly reduced by day 5, but some infection was still observed. Understanding the epidemiology of P. capsici in irrigation water sources is essential for designing effective management strategies.

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