Evaluation location: Washington, United States
The screening took place in the greenhouse located at the Washington State University / USDA-ARS Research Station Campus by Prosser, WA. The study was carried out in pots. Initially, true potato seeds (not tubers) of 40 accessions of S. tuberosum subsp. andigenum were grown and 15 plants were selected to represent each accession. The first screening trial was carried out during 2007, with Russet Burbank and Ranger Russet as industry standards for comparisons. Among the 40 accessions screened, 5 demonstrated less (P<0.05) disease on both root and stem compared to the standard cultivars. These 5 accessions were considered "potentially resistant" to black dot. In 2009, a fresh batch of 100 seeds of each of the "potentially resistant" accessions was obtained. The seeds were grown into plants, each a unique genotype, and from each accession 10-15 genotypes were selected based upon their vigor. The genotypes were propagated into multiple copies (clones) and were maintained as plants in the greenhouse, as tissue cultures and as tubers. The genotypes were screened with 8 to 26 replications each; and resistance was recorded based upon stem colonization in comparison to Russet Burbank, Shepody and Umatilla Russet that were used as industry standards. Five black dot resistant clones were identified from the accession PI243367 and 2 from the accession PI230470.