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News - 30-06-2023

Denomination of new official downy mildew races in lettuce

On 1 July, the European committee of the International Bremia Evaluation Board (IBEB-EU) published three widely occurring new variants of downy mildew in lettuce: Bl:38EU, Bl:39EU and Bl:40EU. A considerable number of vegetable breeding company Rijk Zwaan’s current lettuce varieties are resistant to these three new races.

New officially denominated races

Downy mildew can damage lettuce leaves in both protected and open-field crops, resulting in a loss of yield. The new variants of downy mildew (Bremia lactucae or Bl) have been found across Europe, but only one or two races are present in most areas. IBEB-EU expects these variants to spread further in the summer and autumn of this year, although it is currently difficult to predict which areas will be more or less affected.

Moving forward with robust crops

Downy mildew is evolving genetically all the time. “At Rijk Zwaan’s phytopathology research facility, we conduct extensive year-round testing on our lettuce varieties to observe if they are resistant to the different Bremia races,” explains Hans van der Schee, Assistant Phytopathology Implementation.

“We share our results with Rijk Zwaan’s lettuce breeding teams so that they can select only those varieties that demonstrate resistance. This keeps lettuce growers moving forward with robust crops,” he adds.

The development of resistances against downy mildew is one of the pillars of Rijk Zwaan’s lettuce breeding programme. The company’s crop specialists are happy to explain more about the current range of lettuce varieties and their resistances.

Sustainable solutions

Rijk Zwaan is a strong advocate of integrated pest and disease management in order to reduce the risk of disease outbreaks. While resistant varieties play a vital role, the company also recommends the use of appropriate crop protection agents – and always with restraint – to prevent new downy mildew variants from developing. Moreover, implementing good hygiene practices, such as promptly ploughing under crop residues and diseased crops, can help to reduce the spread of downy mildew in lettuce.

International Bremia Evaluation Board

The International Bremia Evaluation Board (IBEB) is a joint initiative of lettuce breeding companies in the USA, France and the Netherlands, the USA’s University of California-Davis, the Netherlands’ Inspection Service for Horticulture (Naktuinbouw) and the French National Seed Station (GEVES). IBEB’s mission is to identify new races of Bremia lactucae that pose a significant threat to North American or European lettuce production and to promote the use of standardised race names in communication with growers.

Races are identified and nominated by regional IBEB committees specifically for each continent. For more information, visit the International Seed Federation’s website.

The races Bl:16-28EU of  Bremia lactucae are hardly observed in practice in Europe anymore and thus have no value for describing resistance levels to the disease. Therefore, from 1 July 2023 onwards, commercial resistance claims for lettuce varieties will refer only to Bl: 29EU and races with a higher number, and no longer to races Bl: 16-28EU.

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