Lettuce variety selection is such an intricate process that Rijk Zwaan’s current demo field on Pleroma Farm, outside Brits in the North West Province, entails 110 varieties, where a similar trial for cucumbers might consist of five or ten varieties.
Every processor and every retailer has a different set of specifications, compelling a lettuce grower to invest in diversity. “You need two or three green varieties and two or three reds at any given time,” says a major South African leaf vegetable grower.
One of the biggest headaches for a lettuce grower is the percentage unusable weight or, in other words, the percentage of a head of lettuce lost to wastage – leaves that are too yellow, too big or too mature.
Leaves being lost is, in fact, lost energy. “We want to transform as much of the growth energy as possible into marketable product,” explains Gerhard Smit, commercial manager of Rijk Zwaan in South Africa.
Lettuce with the Knox trait
Another factor leading to wastage is oxidisation of the cut surfaces, turning a pink-brownish colour. Rijk Zwaan has specifically addressed that challenge through lettuce varieties carrying its Knox trait which delays the process of oxidisation.
Lettuce with the RZ Knox trait isn’t on the South African market yet but Rijk Zwaan South Africa is working hard at getting it on the South African market. Overseas trials have found that it can give an extra one to two days’ of shelf life, but to determine the value of lettuce with the Knox trait under South African conditions, the local RZ team is going to conduct an investigation of it throughout the entire chain, from the production end right through to the retailer and consumer.
At its 2017 field day, Rijk Zwaan introduced some new concepts to growers, the Green Batavia Knox 81-296 RZ, so-called sandwich leaf Batavia, bred for more and smaller leaves (roughly the size of a hamburger) and for crunchiness. The Knox 81-296 RZ allows for very little wastage because of its leaf size. Growers attending the open day were impressed by the new variety.
In the Green Butterhead range, Fabietto and Sandalina are both well-regarded as the standards in the local industry. New varieties 43-102 RZ and 43-147 RZ have demonstrated good results, as compared to the former. “We’re trying to find a variety that’s growable under winter conditions while still giving a good head,” says Smit.
Comparison of Red Batavia varieties
Salanova range
Growers are looking for red leaves showing sharp colour contrast between the burgundy and the green, with a good balance between the colours. The Knox 79-209 RZ Salanova red butter head impressed them on that count at the open day.
“We’re very excited about the first Salanova Red Cos, it’s the first Salanova Cos variety,” Smit says of 79-688 RZ, which is undergoing phase 3 trials. “It offers uniformity of leaf, good colour penetration and it seems to be more bolting tolerant. We will look how it compares throughout this coming summer.”
A new trend is lettuces that are handled and cut as little as possible, placing much emphasis on leaf size and uniformity of leaf size. Rijk Zwaan’s Salanova concept answers to these requirements and its worth as a high-value component to salad mixes is well appreciated by local processors.
The new Knox Exam RZ, a Salanova Incised Leaf type, won’t only be suitable for mechanical harvesting (a development eagerly awaited by South African lettuce growers who still harvest manually) but it is “a beautiful bag-filler”.
Knox Exam RZ, showing the abundant volume from a single head
As for Salanova Red Incised and Crispy, Telex RZ has been found to be a good cultivar for summer conditions (the redder a leaf, the more heat stress it experiences). Halflex RZ , its follow-up, will be trialled under summer conditions.
Two new varieties are available in the Lollo Bionda range, Landau RZ, which is a darker green than the current standard Levistro RZ and Lungavilla RZ that has the same blonde colour but a bit better volume. “A full-blown Lollo Bionda, it has a broad leaf, if one’s looking for a variety for a pillow pack with the benefit of a Salanova. Viatic RZ and Vilar RZ are two great alternatives,” Smit advises.
Varietal development against Fusarium is another major focus.
For more information:
Gerhard Smit
Rijk Zwaan
Tel: +27 76 300 7860
Email: g.smit@rijkzwaan.co.za