Breeders talk about their lengthy quest for Knox™
Johan Schut: “When I joined the company in 1998, fresh cut and bagged lettuce was starting to take off. We were in contact with processing companies in the USA and the UK, among other countries. Pinking along the cut edges was proving to be a key problem, so as part of our breeding programme we were keen to find a lettuce variety that would be strong against pinking.”
Screening 10,000 plants
“From 2003 onwards, in the pre-breeding phase, we first looked for the right screening method. After all, we work with seeds from a huge number of different lettuce types. How can you determine the pinking rate of a head of lettuce after washing, cutting and bagging? That would be a logistical nightmare with so many different plants. So we wanted to figure out a smarter approach. After countless tests we found the best method to reproduce the slightly moist environment found inside a bag of lettuce.”
Cream cakes for the team
“We removed a one-centimetre disc from a leaf of each plant and placed it on wet filter paper. After a couple of days we saw the paper around the leaf disc turn pink in all of the samples…until we came across one without a pink ring. It looked very promising – that had to be the one! Thankfully, tests with the original lettuce plant and further trials with its offspring confirmed what we hoped – we’d found a source that delayed pinking in lettuce.”
The art of breeding
Egbert Smits adds: “2007 marked the start of the breeding phase, which is my speciality. We’d found the gene in a butterhead lettuce. The art lies in crossing the trait into other types of lettuce, from oakleaf to iceberg, including lettuce types that are very far genetically removed from butterhead. At the same time, it’s important to retain all the other good traits such as resistances, colour, size and harvesting period. When I’m out in the field selecting plants, I always have a ‘top ten’ of criteria in my mind. Sometimes just two crossings will be enough, but other times you will need as many as five. And each round of crossing takes between six and nine months.”
Never finished
Eight years later Rijk Zwaan had managed to cross the natural trait into commercial plant material. Smits: “By the time of the launch in 2015 we had some varieties containing Knox available for almost all lettuce types – there are currently ten varieties in total. And we’re continuing to work on more. Myself, I’m responsible for the Salanova Crispy types, and we currently have around six in the trial phase. New ones will be added every year until our most important lettuce varieties all have the Knox trait.” Schut: “We’re pleased that this is such a success because we’ve spent a long time working on it. But our work is never finished; we’re always trying to further improve our varieties. That’s the great thing about being a breeder.”
Martine Boekestein
Rijk Zwaan Distribution
Burgemeester Crezéelaan 40
PO Box 40 2678 ZG De Lier, The Netherlands
Tel: +31 174 53 23 00
Fax: +31 174 51 21 66
[email protected]
www.rijkzwaan.com
