New resistance breakthrough against adaptable lettuce aphid

It has completely adapted itself to lettuce, hides deep inside the head and multiplies rapidly. We’re talking about Nasonovia ribisnigri, the currant-lettuce aphid feared by all lettuce growers. However, it ignores Rijk Zwaan’s new lettuce varieties with Nr:0,1 resistance. Anneke Kroes, a phytopathologist at Rijk Zwaan, explains how her research contributed to achieving this all-important breakthrough for growers.

“I view the currant-lettuce aphid as an interesting challenge, not only because it’s such a troublesome pest in lettuce crops, but also because it’s important to Rijk Zwaan,” says Anneke. “It was one of the first resistances our company introduced, back in 1996. Unfortunately the resistance was overcome in 2007 because the aphid adapted. That’s why I was keen to play a role in finding a new resistance.” 

Devoted to the aphid 

Anneke, who joined Rijk Zwaan three years ago, has been able to pursue that goal in the company’s phytopathology department, where around a hundred colleagues are focused on pests and diseases. For the past three years, Anneke has enjoyed devoting every workday to the currant-lettuce aphid, which is mainly found in temperate climates worldwide. Her aim? To develop tests as the basis for research into Nasonovia ribisnigri resistance. 

Lettuce specialists 

In order to develop a testing method, she first had to study the currant-lettuce aphid closely. Today, she is an expert on it. “The aphids are usually green, but they can also have a yellow or reddish-brown colour, with characteristic black markings on their legs. They feed on phloem – the living tissue in plants that transports things like sugars and proteins – using an efficient mouthpart called a stylet,” she says. 

Another distinguishing feature of these aphids is that they can only survive on lettuce or endive. “They are real specialists. They have completely adapted themselves to lettuce, making it easy for them to evolve,” explains Anneke. 

Blackcurrants 

However, the aphid actually originated in a different crop: blackcurrants. “That’s how it got the name ribisnigri. The aphids survive the winter as eggs on blackcurrant bushes, where they hatch into nymphs in the spring. After maturing into adults, the aphids then migrate to lettuce crops,” continues the phytopathologist.