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Disease Cycle and Epidemiology

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Phytophthora capsici is a soilborne pathogen and survives between crops as oospores in soil or mycelium in plant debris. Oospores are resistant to desiccation, cold temperatures, and other extreme environmental conditions, and can survive in the soil, in the absence of a host plant, for several years. Oospores germinate and produce sporangia and zoospores. Zoospores are released in water and dispersed by irrigation or surface water. Zoospores are able to swim for several hours and infect plant tissues. Zoospores first lose their flagella and then encyst and form a cell wall, germinate and infect plant tissues. Abundant sporangia are produced on infected tissues, particularly on affected fruit. Sporangia are dispersed by water or in wind-driven rain in the air. Sporangia may either germinate directly and infect the host plant or germinate and give rise to zoospores that are released in water and infect the plant. The pathogen grows within the host and produces sporangia on the surface of the infected tissues. If the environmental conditions are conducive, the disease develops rapidly. Although the pathogen produces chlamydospores on culture media, their role in pathogen survival and diseases epidemiology is not known.

Soil moisture conditions are important for disease development. Sporangia form when soil pores are drained, and they release zoospores when soil is saturated (soil pores are filled with water). The disease is usually associated with heavy rainfall, excessive-irrigation, or poorly drained soil. Frequent irrigation increases the incidence of the disease. Warm conditions are favorable for disease development.