ARS | Publication request: Comparing New Zealand and United Kingdom isolates of Phytophthora kernoviae

Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: March 10, 2008
Publication Date: July 28, 2008
Citation: Widmer, T.L. 2008. Comparing New Zealand and United Kingdom isolates of Phytophthora kernoviae. Phytopathology. 98:S171

Technical Abstract: Phytophthora kernoviae was discovered in the United Kingdom in 2003, and identified as a new species in 2005. Recent DNA sequence studies identified two unknown Phytophthora isolates collected in the 1950s and 2002 in New Zealand as P. kernoviae. The purpose of this study was to compare two isolates originating from New Zealand (PK-1 and PK-2) and two originating from Cornwall, UK (PK-3 and PK-4). Mycelial growth on agar plates was similar for all isolates at 5, 10, 15, 20, 25, and 30 degrees C. Sporangial production was about five to 10 times higher in liquid cultures for PK-3 and PK-4 than PK-1 and PK-2. However, isolate PK-3 could not be induced to release zoospores. P. kernoviae is homothallic and easily produces oospores in culture. Oospore production was similar for PK-1, PK-2 and PK-4, which were about three times higher than for PK-3. Inoculation of Rhododendron leaf disks with sporangial or oospore suspensions showed little difference in necrosis among the isolates, except for PK-3, which showed very little necrosis. Whole plant inoculations of Magnolia stellata and Rhododendron “Cunningham’s White” showed higher necrosis when inoculated with sporangia of PK-1 and PK-2. These results show differences between the New Zealand and UK isolates. Future tests should include at least one isolate from each geographic location.