The Netherlands
March 2011
The International Bremia Evaluation Board has evaluated all Bremia races found in 2010 and races found earlier. In 2010, most outbreaks of Bremia were again caused by new Bremia races with only local importance. However IBEB was able to identify and nominate a new race Bl:28. The Board emphasizes the importance of chemical control and hygiene measures in addition to the use of resistant varieties to prevent the development of new races.
Bremia lactucae, or downy mildew fungus in lettuce, is very variable. Even within one lettuce production field and within one isolate from a field, several races may be present. On Friday, November 26th 2010, the International Bremia Evaluation Board (IBEB) met in Paris to evaluate the Bremia lactucae races found in Europe in 2010. About 46 isolates were lacking the ability to break important resistance genes used in common lettuce varieties. About 127 isolates (37%) of all 343 infestations concerned previously described and officially nominated Bl: races, mostly Bl:22, Bl:24, Bl:25, Bl:26 and Bl:27 or closely related races (“Bl:” is the official code for races of Bremia lactucae).
As usual, most of the isolates encountered in 2010 were of minor importance because they disappear quickly. Only one of the newly found and evaluated races since 2009 was important enough to be nominated as Bl:28. Bl:28 has evolved from Bl:24 and breaks the resistance in several lettuce varieties with resistance to Bl:1-27. These varieties are possessing resistance resulting from a gene in the extended determination set of last year. The identifying sextet-code of this new Bremia race is 59-31-10-05. Bl:28 was found 10 times in 2009 and 2010 in France, The Netherlands, Belgium, Germany and Spain. Isolates with a very similar virulence pattern were found 15 times in 2010 in the same countries and Italy.
The board emphasizes that although breeding companies supply growers with lettuce varieties possessing resistance to the nominated Bl:1-28 isolates, it is not a full insurance against Bremia. The resistance gives the grower a basic protection. Local breakthrough of resistance on specific varieties by an isolate that cannot survive over years and spread to other areas, may occasionally cause problems.
The board emphasizes also the importance of chemical control and hygiene measures in addition to plant resistance. Fungicide application, especially in a young plant stage, gives additional protection to resistant lettuce crops, which will help prevent the development of new Bremia races. Proper hygiene practices, such as removal of debris and diseased plants and cleaning shoes after field visits, will reduce the spread of Bremia in lettuce crops.
The IBEB consists of representatives of the Dutch and French seed business associations Plantum NL and UFS, and the organisations of GEVES and Naktuinbouw. IBEB is supported by several Bremia investigators across Europe. The business associations were represented by lettuce breeders of Agrisemen, Enza Zaden, Gautier, Nunhems, Rijk Zwaan, Monsanto Seminis, Syngenta and Vilmorin.
For testing and breeding purposes all nominated races and EU-B determination set are available at GEVES/SNES (France) and at Naktuinbouw (The Netherlands).
For more information please contact Mrs. Valérie Grimault, SNES-GEVES France,
telephone +33 (0)2 41 22 58 00 or by e-mail: Valerie.Grimault@geves.fr
You may also contact the Naktuinbouw Variety Testing department,
Mr. Diederik Smilde, Mr. R. Ludlage or Mrs. A. van Dijk,
telephone +31 (0)71 33 26 213 or by e-mail: Resistentie@naktuinbouw.nl
Topics
Species
