A new race of the downy mildew pathogen (Peronospora farinosa f. sp. spinaciae = P. effusa) on spinach was first identified in March of 2015 in Salinas, CA, U.S. This race was able to overcome most of the race 1-15 varieties evaluated. The isolate, originally designated UA201519B, was characterized based on disease development on a standard set of differential varieties. Subsequently, isolates with the same reaction pattern on the differential set have been found in numerous locations. After careful evaluation of the significance of this development to the spinach industry, the International Working Group on Peronospora (IWGP) has denominated isolate UA201519B race Pfs: 16.
Race Pfs: 16 is able to infect the differentials Viroflay, Resistoflay, Clermont, Lazio, Pigeon, and Meerkat, but not able to infect Califlay, Campania, Boeing (Avenger), Lion, Whale, and Caladonia.
The IWGP is continuously monitoring the appearance of strains of the pathogen that deviate in virulence from the known races. In this way the IWGP aims to promote a consistent and clear communication between public and private entities, such as the seed industry, growers, scientists, and other interested parties about all resistance-breaking races that are persistent enough to survive over several years, occur in a wide area, and cause a significant economic impact.
The IWGP is located in The Netherlands and is administered by Plantum NL. The IWGP consists of spinach seed company representatives (Pop Vriend, Monsanto, RijkZwaan, Bayer, Takii, Sakata, Bejo, Enza, Syngenta, and Advanseed) and Naktuinbouw, and is supported by research centers at the University of Arkansas and the University of California Cooperative Extension (Monterey County) in the U.S. Researchers all over the world are invited to join the IWGP initiative and use the common host differential set to identify new isolates.
For more information on this subject you can contact Jim Correll (jcorrell@uark.edu), Steve Koike (stkoike@ucdavis.edu), Diederik Smilde (d.smilde@naktuinbouw.nl), or the IWGP chairperson Jan de Visser (JandeVisser@popvriendseeds.nl).
Disease reactions of race 16 (UA201519B) observed on spinach differentials by the IWGP compiled February 2016.
aDisease reactions observed in controlled inoculation tests
by the participants of the IWGP. “+” indicates
susceptible; “-“ indicates resistant disease reaction.