Differences in virulence and sporulation of Phytophthora kernoviae isolates originating from two distinct geographical regions

Authors: Widmer, Timothy

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/31/2014
Publication Date: 4/1/2015
Publication URL: http://handle.nal.usda.gov/10113/60701
Citation: Widmer, T.L. 2015. Differences in virulence and sporulation of Phytophthora kernoviae isolates originating from two distinct geographical regions. Plant Disease. 99:460-466.

Interpretive Summary: A recently discovered plant pathogen in the United Kingdom and New Zealand has been found to attack many different hosts. Although not currently known to exist in the United States, it is a pathogen of concern due to its destructive nature and threat to valuable hosts in the U.S. We performed this study to learn if there are any differences in causing disease and production of spores between cultures collected in the United Kingdom and those collected New Zealand. Results show that those cultures originating from the United Kingdom caused more disease symptoms on three selected plant species than the cultures from New Zealand. In addition, different spore types were produced on the leaves of the tested hosts and were comparable to other similar species of this pathogen already present in the U.S. These results provide information to regulatory agency personnel and scientists to develop guidelines that help in limiting the spread of this pathogen and show that it is a threat to spread within the U.S.

Technical Abstract: Phytophthora kernoviae has only been isolated from the United Kingdom (U.K.) and New Zealand. To understand what differences may exist between isolates from these two distinct geographical regions, virulence studies on three host plants and sporulation on host leaves were conducted on select isolates. Three host plant species, Rhododendron ponticum, Magnolia stellata, and Annona cherimola, were inoculated individually with sporangia of six different isolates from each geographical region. Results showed an overall higher virulence on all three hosts from isolates originating from the U.K. After inoculation, P. kernoviae sporangia and oospore formation on different host leaves were observed and compared to P. cactorum and P. syringae. Results were host dependent with P. kernoviae producing generally similar or above amounts of both propagules compared to the other U.S. indigenous species. These results have implications for regulatory agencies and scientists who are interested in preventing its entrance into the U.S. and learning more about its potential spread.