From hybrid to climate-proof onion

Jan Slot joined DGS as an employee in 1973. At the time, the company was a small player in the market: it had the varieties, but lacked a good sales force. That changed when DGS entered into cooperation with Jacob Jong. That collaboration was the breakthrough, says Jan Slot. "There was new material to innovate, such as Robusta and Balstora, other Rijnsburger varieties. And there was a good sales force, both in the Netherlands and internationally, which managed to take both companies further."

Better storage onions 
The first hybrid Rijnsburger on DGS's variety list was Hygro (1973). The breakthrough came with Hyton in 1982, which became the largest variety in the Netherlands. Hyton delivered kilos and had good skin quality and better storage quality, says Slot. "Growers were looking for better storage onions, which could be stored beyond April. Even then, there were different varieties for different markets." With Hyton, growth came a long way for DGS, he says, although he personally liked Hygro better in colour. 

Hybridisation resulted in a more uniform product, with a finer neck, earlier varieties and longer storability. Because the crop was nicely even on the land, it became easier to treat the plants against diseases and pests. The open pollinated varieties disappeared from the list, except Red Baron (1984). This red variety with a high yield and good storability is especially popular with growers on relatively heavier clay soils.

In the mid-1990s, varieties such as Hyskin, Armstrong and Summit entered the market. Hyskin was the big follow-up to Hyton; Armstrong and Summit are still used today. Initially, the market did not take off; the acreage in the Netherlands was too large, says Slot. "A symposium was held and onion cultivation was advised to go back from 10,000 to 6,000 ha, an acreage size that made the Dutch market self-sufficient." Soon, the price of onions went up again, so that the acreage was increased to 8,000 ha that same year. "Growers also started to mechanise more and more at the turn of the century and the global population increased rapidly. As a result, exports shot up." 

Resistant varieties
At the same time, breeding of resistant varieties began. Growers occasionally had major problems with downy mildew and leaf spot, says Slot. "Plant protection products against mildew did exist, but they were not cheap. We did manage to develop resistant lines per se, but it took a long time before the resistant product actually started to look like an onion," he laughs. At the time, DGS also went in search of a head-rot-resistant onion, but failed.

The first commercial Rijnsburger with high resistance to mildew was Hylander (2010), Hysky (2013) was the first variety for the Rijnsburger market with fusarium tolerance. Slot: "At the time, fusarium was also becoming an increasing problem, due to global warming and higher soil temperatures. Hysky was a variety specifically for Dutch onion cultivation, but it does not have the storage quality of a typical Rijnsburger. Breeding for fusarium tolerance did not happen automatically, which was quite a challenge. But fortunately there are multiple sources, which allows for different variety possibilities."

DGS was also abroad at the time, where the breeding department came into contact with other genetics. Experience was gained with foreign material, although this did not always go well, laughs Jan Slot, such as with Spanish overwintering types. "It was searching for the ideal combinations." For example, Hytune (2015), a continental variety with blood from other daylength types, is doing very well in Poland, he says. "Still a Rijnsburger, but with different genetics. It is an early variety with a good root system, high yields and the onion needs less nitrogen input. Another example is Hysinger, which is recommended due to decreasing possibility of irrigation in Zeeland. This is a drought-tolerant variety.

New challenges
Because climate change brings new challenges in turn. There is a shift towards robust varieties, says Jesper Lam, breeder at DGS since 2019. New varieties should be heat- and drought-resistant, but have enough wax layer to absorb rain. The foliage may be greener, to be less affected by thrips, a pest that is also on the rise. Sowing is increasingly late and there is a greater chance of rain at the end of the growing season, which brings more uncertainty for harvest time. The changing climate also brings a shift of diseases and pests, such as pinkroot and Stemphylium. "The trick is to keep the crop healthy for as long as possible," he says.

Another challenge is the expected loss of approval for the sprout inhibitor MH, in 2032. "The onion sector has the varietal advantage of longer shelf life. If you leave the onions in the shed, you can safely keep them for a long time. But during export, the onions are in a container for six to seven weeks. Then they will always sprout. In this piece of export, chemistry cannot really be missing," says Lam.

Breeding does not yet have an answer to the removal of the sprout inhibitor. "You're not going to change anything about the onion itself," he continues. Greener harvesting could be a solution or container adaptation in the form of refrigeration. "There is a risk that without an alternative to the current MH, the market will come under pressure."

Multi-resistant onion
Whereas Jan Slot's 46-year career was mainly dominated by hybrid and resistant varieties with higher production/yields, better quality and more uniformity, for Jesper Lam the challenges lie mainly in resistant, durable and climate-proof varieties. We need to move towards onions that can develop a lot of foliage in a short time to cope well with late sowing, says Lam. "Furthermore, we have to respond to the fact that fewer and fewer chemical agents are allowed to be used. This calls for a multi-resistant onion against diseases like powdery mildew, fusarium and pink rot. But the product must retain the highest quality with all these characteristics."