New downy mildew race identified

Enza Zaden is ready with highly resistant varieties

A newly identified race of Bremia lactucae, the pathogen responsible for downy mildew in lettuce, has been confirmed by the International Bremia Evaluation Board – United States (IBEB-US).
Designated Bl: 10US, this race presents a new challenge to U.S. lettuce production, particularly in California’s Salinas and Imperial Valleys, where downy mildew pressure is consistently high.

Bl: 10US has emerged with strength, demonstrating the ability to overcome Dm25, Dm38, Design and several other genes. This reinforces the importance of local research to address the pathogen’s well-documented capacity to evolve rapidly under selective pressure.

Local solutions

These developments highlight the critical role of local research in identifying threats and breeding effective resistances. As a vegetable seed breeding pioneer since 1938, Enza Zaden believes in delivering local solutions. The company invests in 36 local R&D stations across 24 countries, and reinvests 30% of annual sales into ongoing research.

“At our R&D station in San Juan Bautista, CA, we breed for the specific challenges of western U.S. lettuce-growing regions, which includes careful monitoring of pathogen threats. With B1:10US recently named, we’re pleased to have several highly resistant varieties available now. We are also in the process of advancing more pipeline varieties as we continue to evaluate the impact of the new race and other emerging threats facing lettuce growers,” said Julie Butcher, Product Manager, N&CA Open Field Whole Head Lettuce and Brassica.

Commercially available Enza Zaden varieties showing high resistance to B1:10US include (but not limited to):

Romaine: Adicamp, Almanor and Jara.
Babyleaf: Cavendish, Clearwater, Leucadia (new), Mosslanding (new), Carpinteria and Kinlar.
Eazyleaf: Ezpark, Ezbourne, Ezflor and Asakgreen.

While no crop can be guaranteed free from downy mildew, the combination of highly resistant varieties – such as these from Enza Zaden – together with appropriate chemical protocols and preventive agricultural practices offers the most effective strategy for successful lettuce production.

For updates and more information, visit www.enzazaden.com

Source: Information on Bremia lactucae Bl:10US sourced from International Bremia Evaluation Board – US (IBEB-US) press release, published July 1, 2025