MANAGEMENT OF DAMPING-OFF CAUSED BY PYTHIUM SPP. IN ORGANIC VEGETABLE PRODUCTION IN THE PACIFIC NORTHWEST
Alcala, Ana Vida Crisostomo
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Vegetable production is an important sector of the organic food industry in the Pacific Northwest USA. Significant acre s of organic vegetable crops, particularly processing green pea and sweet corn, are grown in the semi- arid Columbia Basin of central Washington and north central Oregon, where Pythium damping -off can cause losses in early spring when cool and wet soil conditions are conducive to the disease . In this study, 37 certified organic fields were surveyed in the Columbia Basin for Pythium species, from which 305 isolates were bai ted and identified to 19 species . Pathogenicity tests of isolates of each species on pea in cool and wet soil conditions revealed isolates of 9 species were pathogenic, with differences in virulence among species and among isolates within species . P ythium ultimum (24.6% of the 305 isolates), P. irregulare group 1 (15.1%), and P. abappressorium (4.9% ) were the most prevalent pathogenic species . Real -time PCR assays detected P. ultimum in 100% of the 37 fields compared to 78% for P. abappressorium , and 57% for P. irregulare group 1.