BRASSICA MAGAZINE
RESEARCH
NOT JUST ONE CAUSE Wageningen UR does fundamental research into the causes of blindness. Seed companies carry a large part of the costs, because research focuses on the underlying genetics. The study is a broad one, including research into problems such as headlessness in tomato plants. The commission heading the research is known as the “Headlessness Board”. Yet it’s unclear whether headlessness and heartlessness are related. The board’s chair is Corine de Groot of Bejo Zaden. Because it is paid research and not all seed firms participate, most findings are kept a trade secret. Researcher Jennifer de Jonge did her doctoral work on blindness: her work clarified which area of the genome is responsible for the problem. However, there are dozens of genes in that area that might be responsible. Further research will be needed to discover which are the affected genes.
The research did suggest that germination conditions could influence blindness, but it was unclear what exactly was involved. It does seem to be the case that cold in the first days of germination leads to more blindness. A surprising discovery was that molybdenum and other minerals have no influence on the incidence of blindness. After 50 years of fertilizing with molybdenum, this standard growing procedure can go out the window. De Jonge also found that moistening the seeds and then drying them made them somewhat less vulnerable, though whether this works for all batches of seeds and all varieties remains to be seen. A newly developed test for blindness can also show whether a particular lot of seeds is unusually subject to blindness. Bejo will apply the research in its breeding and seed production as it works to prevent blindness.
Kohlrabi is highly susceptible to blindness. Its sibling broccoli is less vulnerable, but even so, a grower can still suffer serious losses. “Some varieties are more prone to blindness than others. That’s something plant propagators need to be aware of,” says William Gitzels, a propagator in Wervershoof, North Holland. Over the years he’s acquired a lot of experience with blindness. “It occurs most often with low temperatures and little sunlight – in other words, in the spring.”
from. “But the second year it rained complaints, because some growers made the same mistake of propagating using convection heating. You just have to keep the plants warm,” Gitzels sums up.
HISTORY Gitzels sketches a history of the search among broccoli growers for the causes of blindness. It began around 1988, when six growers started producing for the wholesaler ‘WFO’. They wanted to supply broccoli early in the season by starting propagation in October, as was already done with cauliflower. They tried germinating with convection heat at a minimum of 5°C, but it soon became clear that at that temperature broccoli would “bolt”: it began to flower much too early. Planting in December and heating to a minimum of 10°C produced fairly good-looking seedlings that could be planted out in March, but after they
had been covered for a couple of weeks, three-quarters of the young plants turned out to be blind. Gitzels soon realized what was happening. At low outdoor temperatures under a clear sky, the thermostat in the greenhouse might be set to 10°C, but heat was radiating out, causing the actual tempe rature of the plants to go a few degrees lower. When plants were propagated using tubular heating, radiant heat went straight to the plants and their temperature stayed at or above 10°C. “Later, when a screen was put up, the number of blind plants went down even further,
EARLY SOWING Growers in England were forcing the Marathon and Lord varieties by sowing them in September, so that before the winter good-sized plants developed that were less prone to blindness. Gitzels tried that too, sowing on September 25 in a 228 tray. But propagating for such a long period in a dark
“ Sensitivity to cold is not the only reason for blindness” because the plant temperature held steady and never went under 10°C. With the plants that were still propagated using a convection heater – and it was a cold winter – there were a lot of complaints.” The first year working with the early variety Sirtaki was a success, Gitzels observes, and it didn’t matter which grower the plants came
winter resulted in plants that looked terrible, Gitzels recalls. He decided to sow in December instead, using roomier 96 trays. “That was in 1992. In December we sowed in 96 trays and in January in 228 trays.” That approach proved successful. In 2014 Gitzels began propagating the December plants under artificial light in both
96 and 228 trays. “Some of my colleagues propagate in Spain. We use SON-T lamps instead. But either way, the time gain isn’t spectacular.” On the other hand, his experiment did yield better-looking plants. “We’ve limited the price increase in the coming season to just the electricity costs. We advise people to order half lighted, half unlighted. If you can supply the market at the start of the season, that makes it worth your while.”
BUCKET Gitzels compares a plant that develops blindness to a bucket that can hold a certain amount of cold. It’s when the bucket overflows that you get problems with blindness. “With convection heating you can germinate nice plants, but when you take the cover off after six weeks, 50 percent of them will be blind. You’ve overfilled the bucket.” Yet it’s still unclear what goes wrong and how, even though research into the causes has been going on for five years. A commission has been set up to oversee research on blindness, with Gitzels as one of its members, along with other plant growers, seed companies, and researchers from Wageningen University.
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