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Carl Collen


Resistance key for organic lettuce

New downy mildew resistance could offer greater security for organic lettuce growers, Rijk Zwaan says

Resistance key for organic lettuce

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Being resistant to diseases and pests is crucial in the organic lettuce market, and Rijk Zwaan, which offers around 60 varieties of organic lettuce, has taken this further with a new horizontal resistance to downy mildew.

This could represent an important next step in the organic lettuce market, according to Johan Schut, breeding manager lettuce at Rijk Zwaan.

“What organic growers look for in a lettuce variety is not actually all that different from their peers who grow lettuce traditionally," explained Schut. "The most important criteria for both groups is 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," he continued. "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.”

Due to the similarity in demands, Rijk Zwaan's breeding programmes for organic and traditionally produced lettuce largely run in parallel, and then prior to commercial launch trials are run separetely for the most highly promising varieties in both categories.

Seeds are produced by certified growers in the Netherlands and Australia, with all 60 lettuce varieties available as organic seeds and not just as non-chemically treated seeds (NCT).

“The biggest challenge in lettuce breeding is the fact that new strains of mildew are emerging all the time," Schut outlined. "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.

Rijk Zwaan has tested its first potential variety, but it will still be some time before varieties are available commercially, according to the company.

“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," Schut added. "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.”

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