Creating lettuce resistant to new downy mildew races

With races of downy mildew in lettuce ever evolving, it’s important to find varieties that provide the resistance support growers need to mitigate yield losses. In the past two years, four new races of downy mildew in lettuce were identified – 38, 39, 40, and 41.

And that number is a count – 41 unique races of this pathogen threaten lettuce growers around the world. More are present in Europe, but multiple types can be found anywhere lettuce is grown.

Most recently, race 41 was officially recognized July 1, 2024, by the International Bremia Evaluation Board (IBEB-EU). It spread to several countries including the Netherlands. Even with races evolving quickly, Syngenta Vegetable Seeds breeders keep a close watch on evolving races and continue to adapt the breeding program to address these challenges.

″It is thanks to the close collaboration between our breeders, our sales representatives, growers and the entire industry that we are able to monitor changes in downy mildew isolates in the field,″ explained Stephanie Sunderhaus, Product Specialist for lettuce and spinach in the Netherlands, Belgium, Germany and Poland.

This collaboration, combined with the development of our own resistance and their integration into different varieties, means that we can now offer lettuce varieties that are resistant to this new isolate. All lettuce segments that we work on now have varieties that are resistant to isolates 38, 39, 40 and now also 41!″ she continued.

Breeding for Downy Mildew Resistance in Lettuce

The more-than 40 recognized unique races of downy mildew are just the tip of the iceberg. The real variation within those recognized races is much higher, which means the pipeline for new resistance needs to be deep and widely available in our breeding material so we can react quickly to the market needs.

″Downy mildew is one of those traits where not having a resistance trait just isn’t an option,″ said Michel de Lange, Syngenta Vegetable Seeds Trait Development Lead. ″It can completely destroy yields and growers just can’t afford to take that kind of risk.″

″We prepare by continuously monitoring our material for the presence of resistance and we invest in R&D operations to allow us to quickly place the latest discovered resistances into our variety assortment. Once resistance is in the assortment, we scale supplies up quickly for introduction to markets.″

″When we bring forward a new variety, the resistance needs to be high – not intermediate,″ de Lange said. ″Because downy mildew impacts the leaves of spinach and lettuce, any visible damage on the plant is not acceptable for our growers.″

Syngenta provides new resistant varieties every year to help offset the challenge of emerging races of downy mildew. These traits take anywhere from three to 10 years to get the newest resistance into our best-in-class assortment.

All in all, it means breeders are predicting the future of lettuce and spinach production – ten years from today.