What’s driving hydroponic lettuce breeding?

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BASF Vegetable Seeds is developing lettuce varieties that can be grown in controlled environment facilities using supplemental lights.

Leafy greens, including lettuce, are the hottest crop when it comes to controlled environment vegetable production. It seems like every month a new greenhouse or vertical farm facility begins operating or an existing operation expands with increased production space dedicated to leafy greens. Many of the leafy greens are grown using hydroponic production systems including nutrient film technique (NFT) and deep water culture.

Peter Does, product specialist hydroponic lettuce and spinach at BASF Vegetable Seeds in the Netherlands, has been doing product development with lettuce for controlled environment production for nearly 25 years. The lettuce varieties are sold under the Nunhems brand.

Peter Does, product specialist hydroponic lettuce and spinach at BASF Vegetable Seeds, has been doing product development with lettuce for controlled environment production for nearly 25 years.

“When I started with the company we sold lettuce varieties for hydroponic production primarily in the Scandinavian countries, with some sales in the United States, Canada, Australia and New Zealand,” Does said. “BASF has been breeding butterhead lettuce varieties for greenhouse production since the 1970s because it is a traditional greenhouse crop in the Netherlands.”

Does said before the development of rockwool as a growing medium for tomatoes and cucumbers, these crops were grown in greenhouses directly in the soil. Tomatoes and cucumbers were grown in rotation with one or two cycles of butterhead lettuce in winter.

“The change to rockwool for cucumber and tomato production was a major driver for crop specialization,” he said. “A lettuce crop in the soil in the winter no longer fit in the combined production cycle with tomatoes and cucumbers. This was a push for the development of summer butterhead varieties that could be produced under glass to make year-round lettuce production possible. Previously winter butterhead production was done in greenhouses and summer butterhead production was done in open fields. In standard greenhouses where supplemental artificial light was not an option, this was a form of controlled environment agriculture, but not at the level lettuce growers achieve today.”

BASF has been selling a wide range of lettuce types to hydroponic growers. In 2006 the company built new greenhouses with dedicated breeding and facilities for hydroponic production.

In 2006 BASF Vegetable Seeds built new greenhouses with dedicated breeding and facilities for hydroponic production.

“Basically all the lettuce grown in greenhouses today is produced in some type of hydroponic system,” Does said. “I don’t know of many growers anymore who are producing in soil. Globally the production is changing rapidly. In Europe production in soil has almost disappeared in the last five years. 

“In Europe most of hydroponic lettuce production is with NFT systems. The majority of growers are producing single head lettuce grown in peat pots, which sit in a NFT system.”

Breeding for supplemental light production

Because an increasing amount of lettuce is being produced hydroponically with supplemental light, BASF is focusing its breeding to meet the market demand.

“We look for varieties that perform well under supplemental light,” Does said. “If supplemental light is supplied at a level in the greenhouse starting at 100 micromoles, then the lettuce varieties are potentially suitable for year-round production. If a variety is selected under high supplemental light levels, it normally also performs under lower supplemental light levels but just grows slower.

“Sometimes a variety works year round. Sometimes a summer and winter variety may be needed based on the specific strengths of a variety, including tipburn resistance, heat tolerance and growing speed.”

Does said the future for greenhouse lettuce production in areas with low light levels is tenuous if supplemental lighting is not used.

BASF’s lettuce breeding selection occurs under LED supplement light during the winter.

“Traditionally there were butterhead varieties that were produced in the winter under low light levels like in the Netherlands,” he said. “Light levels in some cases were almost zero. These were varieties that were selected specifically to grow at low light levels and low temperatures. Under these conditions plants grew at a very slow production rate.

“Growing butterhead varieties under winter conditions, it could take five months from seed to harvest. Growers who want to grow lettuce year round need to go to a certain level of high tech. Growers will have to apply supplemental light if they are in an area where the light levels aren’t high enough during the winter.”

Vertical farm applications

In addition to breeding lettuce varieties for greenhouse production, Does looks at their performance in vertical farm systems.

“For me vertical farming is just another form of controlled environment production,” he said. “There is a little more control over the production conditions in a vertical farm compared to a modern high-tech greenhouse. What we select for in regards to breeding for greenhouse production is not that different for vertical farming.

“If we select varieties for production in a high-tech greenhouse during winter in the Netherlands, more than 90 percent of the light is coming from LEDs. That isn’t that much different from a growing system where natural daylight is blocked out completely. What I see is a good correlation from the performance of varieties under greenhouse hydroponic winter production compared to the performance in an indoor vertical farm.”

Peter Does said market changes are asking that lettuce be grown at high densities for mechanical harvesting to deliver maximum yields.

Market changes impact lettuce production

Does has seen a market shift in the way lettuce is being grown in hydroponic production systems.

“Hydroponics was always about growing single heads for the fresh market,” he said. “Traditionally in the United States almost all greenhouse lettuce produced in hydroponic systems was butterhead for fresh market sales. In recent years, the market is increasingly changing toward convenience. Today fewer people are buying a head of lettuce or a whole cabbage or other vegetables in their original state. Many vegetables now end up in a bag or clamshell for ready-to-eat consumption. If the market continues to go in that direction, more growers will start producing different types of lettuces suitable for mechanical harvesting.”

Does said the challenge for growers will be how to optimize production while maintaining quality.

“Market changes are asking for lettuce that can be grown at high densities, mechanically harvested and delivering maximum yields,” he said. “It is no longer about the number of heads of lettuce. Now growers need to produce as many kilograms as possible per square meter per year. At the same time the lettuce has to be a good quality product that has good taste, good texture and good shelf life. This is changing the market. Growers have to find a good balance between density, production cycle, maintaining quality and optimizing yields.”

For more: Peter Does, Nunhems Netherlands BV; peter.does@vegetableseeds.basf.com

Carlos Umana, Nunhems USA Inc., (603) 343-4495; carlos.umana@vegetableseeds.basf.com; https://www.nunhems.com/us/en.html; https://www.nunhems.com/us/en/Varieties/LTL_lettuce.html.

This article is property of Urban Ag News and was written by David Kuack, a freelance technical writer in Fort Worth, Texas.

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