Phytophthora blight can occur on more than 50 plant species (Tian and Babadoost, 2004). There are numerous phases of Phytophthora blight including:
Rot of crowns/stems, roots, and fruit
Foliar blight
Seedling damping-off
Phytophthora blight is caused by the fungal-like organism Phytophthora capsici. P. capsici overwinters in soil and infected plant debris as thick-walled oospores and mycelia. P. capsici is a heterothallic species requiring two compatible mating types (i.e., A1 and A2) for sexual reproduction. Oospores can remain viable for several years. Oospores germinate to form sporangia as soil temperatures rise and moisture levels approach field capacity (Babadoost and Zitter, 2009). Sporangia are caducous and easily dislodge from the sporangiophore. Sporangia may germinate and directly infect a host, or differentiate to form 20 to 40 motile zoospores (Hausbeck and Lamour, 2004). Zoospores are released in the presence of free water. Zoospores and sporangia are dispersed by splashing rain, surface water, and irrigation water. Abundant sporulation on infected tissues results in secondary cycles of infection and disease. Phytophthora blight is favored by warm, wet weather.
References:
Babadoost, M. and Zitter, T. A. 2009. Fruit rots of pumpkin: a serious threat to the pumpkin industry. Plant Disease 98:772-782. doi:10.1094 / PDIS-93-8-0772
Hausbeck, M. K., and Lamour, K. H. 2004. Phytophthora capsici on vegetable crops: Re- search progress and management challenges. Plant Dis. 88:1292-1303.
Tian, D., and Babadoost, M. 2004. Host range of Phytophthora capsici from pumpkin and pathogenicity of isolates. Plant Dis. 88:485- 489.
A white, moldy appearance on the fruit surface is characteristic of Phytophthora fruit rot. The fruits later collapse.
Permanent wilt of a summer squash plant infected with P. capsici. Wilt symptoms develop after root rot progresses into the crown.
Since Phytophthora blight is a soilborne disease, it typically occurs in patches.
