Identification and Characterization of Resistance to Phytophthora infestans in Leaves, Stems, Flowers, and Tubers of Potato Clones in the Pacific Northwest.

Resistance to Phytophthora infestans in leaves, stems, flowers, and tubers of eight cultivars grown commercially in the Columbia Basin and 29 advanced clones from the Tri-State Potato Variety Development Program was quantified. Foliage of all eight cultivars was susceptible in field and greenhouse tests. Six advanced clones had high levels of resistance in stems and leaves in the field at Mount Vernon, WA, but only two of these six clones had high levels of resistance in leaves and stems in greenhouse tests. Flowers of most plants with high to moderate levels of foliar resistance were susceptible to infection in both the field and greenhouse. Tubers of Umatilla Russet, Russet Legend, Gem Russet, and nine advanced clones, including A90586-11, had high levels of resistance in most laboratory tests. Level of foliar resistance against US-8 and US-11 clonal lineages of P. infestans was variable among clones, but tuber resistance by pathogen clonal lineage varied little among clones. Clones with high resistance expressed quantitative differences compared with susceptible cultivars and likely possess a high level of partial resistance.