Latent Infection of Potato Seed Tubers by Phytophthora infestans During Long-Term Cold Storage

Latent infection of potato seed tubers by Phytophthora infestans was determined following inoculation Of tubers and typical seed tuber storage conditions in the Pacific Northwest. Severity of late blight increased over 182 to 209 days during two storage seasons at mean temperatures of 4.1 and 4.2 degrees C. From 0 to 44% of inoculated tubers sampled at given intervals were asymptomatic. However, P. infestans sporangia were observed on slices from these tubers when incubated in a humidity chamber at 15 degrees C or late blight symptoms developed in asymptomatic tubers obtained following storage when incubated at 22 to 23 degrees C for 3 weeks. Development of P. infestans sporangia and symptoms of late blight in asymptomatic seed tubers indicated latent infection of tubers by P infestans during long-term cold storage. Sporulation was observed after 21 to 24 h on symptomatic tubers and 6 to 20 days on asymptomatic tubers that were removed front storage and incubated in I humidity chamber at 15 degrees C. Latent infection of seed tubers and production of viable sporangia of P. infestans were demonstrated after long-term cold storage of infected potato tubers.