New downy mildew resistance could give organic lettuce growers more certainty

Understanding growers' needs

“What organic growers look for in a lettuce variety is not actually all that different from their peers who grow lettuce traditionally. The most important criteria for both groups are resistances to diseases and pests, especially against downy mildew (Bremia) and aphids (Nasanova ribisnigri Nr:1). Besides that, the lettuce must have an attractive appearance, good flavour and not be susceptible to tip burn and bolting. The major difference is that the variety must respond well to organic fertilisers. It’s important for us to have good contact with growers because we want to understand their needs. We’re seeing solid growth in organic lettuce.”

Testing at an early stage

“Because the demands are so similar, Rijk Zwaan’s breeding programmes for organic lettuce and traditionally produced lettuce largely run in parallel. In the phase before commercial launch – phase 3 or even phase 2 – we consciously choose to run trials of highly promising varieties at organic growers, under the supervision of our crop specialists. That allows us to see which lettuce performs well at an early stage. We have a separate organic trial field for open-field crops in Welver, Germany, for the same reason, and propagation is done separately too. Seed is produced by certified growers in the Netherlands and Australia. So all 60 of our lettuce varieties are available as organic seeds and not just as non-chemically treated (NCT).”

Always a suitable variety

“With 60 varieties our organic lettuce range is very extensive, and our customer base includes organic growers from across Europe and beyond. Some of the favourites are the Jerrican RZ red lettuce variety and the green Tombelo RZ which produces large, firm heads of lettuce. In iceberg lettuce the varieties Jasperinas RZ and Diamantinas RZ have been popular among growers for several years. Meanwhile, Kisheri RZ is a green oakleaf variety that is grown widely in Germany and France. Whether they produce in greenhouses or outdoors, organic growers can always find a suitable variety – even for green and red batavia lettuce, lollo bionda, lollo rossa, cos lettuce and Salanova® types.”

Horizontal resistance to downy mildew

“The biggest challenge in lettuce breeding is the fact that new strains of mildew are emerging all the time. We keep incorporating new resistances, but the downy mildew keeps adapting to them, so we’re now looking at a different approach. Some old wild lettuce varieties are less susceptible to mildew. They appear to be more solidly resistant to the disease because there are more genes involved. We call it ‘horizontal’ resistance to downy mildew. The breeding is difficult because it’s harder to identify the components of this desirable trait, but we’re making good progress. We’ve tested our first potential variety, but it will still be some time before varieties are available commercially. This is a very interesting development for both organic and traditional production methods, because it gives growers more certainty of a good harvest.”

Organic lettuce in a bag

“Convenience is an important aspect for Rijk Zwaan when breeding lettuce varieties for the traditional market and has resulted in lettuce in bags, on sandwiches or in salads. Even though that’s still a relatively new market for organic lettuce, I believe it will grow. More and more young people are buying organic vegetables because they want a reliable product that hasn’t involved the use of chemicals. Those consumers are looking for both organic and convenience, and we can meet both of those needs.”