First report of Pythium sylvaticum causing potato tuber rot

Leak is a post-harvest disease of potato tubers manifested by a wet, spongy rot that can quickly lead to complete tuber decay. In North America, leak is most commonly caused by Pythium ultimum var. ultimum Trow, although a number of other Pythium spp. have been found to be pathogenic to potato tubers. We report that an isolate identified by DNA sequencing as P. sylvaticum Campbell & Hendrix was pathogenic to potato tubers. The organism produced a dark, hollow cavity in tubers that was much drier in texture than typical symptoms of leak. Symptomology was similar in tubers of the cultivars Yukon Gold, Green Mountain, and Russet Burbank. Studies to complete Koch's postulates confirmed that P. sylvaticum could be reisolated from diseased tissue and produced the same disease symptoms when isolates were subsequently re-inoculated into healthy tubers. This is the first report of P. sylvaticum causing rot in potato tubers.