• Autumn sowing of sugar beets can shift developmental stages and help avoid summer heat and water deficits at critical times.
  • The greatest challenge in breeding winter sugar beets is combining adequate winter hardiness with resistance to bolting.
  • In Italian trials, autumn-sown sugar beet yielded as much as 80–85 t/ha of roots without irrigation.

Sugar beet as a winter crop? A promising direction for breeding

In Poland, winter crops occupy an important place in the cropping structure, although the range of species grown in this form is relatively narrow. In addition to winter cereals and winter oilseed rape, overwintering leguminous plants have also attracted growing interest in recent years. Interestingly, breeders have also been working for many years to develop sugar beet varieties adapted to winter cultivation.

Faster leaf area development in spring would allow earlier and fuller use of solar radiation, which, combined with a longer growing season, could result in higher root and sugar yields. It is also suggested that autumn-sown beet, by shifting its development stages over time, could avoid peak summer heat and water deficits to a greater extent. It is estimated that yields of the winter form of sugar beet may be about 25 percent higher.

Moreover, an earlier harvest could shorten the period during which the crop is exposed to severe cercospora leaf spot pressure, as well as provide greater flexibility in planning crop rotations.

Two key traits for winter beet

Why, then, have winter beets not yet become widely cultivated in our part of Europe? For years, breeders have been working on two traits that are key to developing a “fully fledged” winter form of beet.

In our latitudes, the basic requirement for breeding winter sugar beets is, of course, achieving an adequate level of winter hardiness—including frost resistance—in the varieties. The beets would have to survive the winter with an adequate plant population and without significant leaf damage, since the leaves are essential for early and effective absorption of solar radiation from the start of spring.

The second important issue is preventing the plants from bolting, that is, producing flowering shoots. Sugar beet is a biennial plant that produces a storage root in the first year of growth and, in the second year, may flower and produce seeds after undergoing vernalization.

When sugar beet is sown in autumn, low temperatures stimulate the plants to enter the reproductive phase in spring. Bolting is undesirable because it comes at the expense of sucrose accumulation in the roots. Winter beet varieties must therefore be genetically resistant to bolting.

Mild winters allow sugar beet to be sown in autumn

Although farmers in Central Europe have so far not seen typical winter forms of sugar beet adapted to harsher winters, autumn sowing of sugar beet is practiced in other parts of Europe. This applies, among other places, to southern Spain and Italy, regions where winters are milder than in Central Europe and the risk of severe frosts is lower.

The beet varieties grown there are not strictly winter varieties in the same sense as, for example, winter cereal or rapeseed varieties adapted to the conditions of Central Europe. Rather, they are varieties selected for autumn sowing and overwintering in a milder climate. Above all, tolerance to lower temperatures and a limited tendency to bolt are important here.

For example, in southern Italy, sugar beets are usually sown from mid-October to mid-November, and harvesting may take place from the end of May to July. As research on growing beets from autumn sowing indicates, overwintering is favored when plants reach the 4–6-leaf stage and accumulate around 300–400 degree-days before the onset of cold weather.

Research results published this year from studies conducted in Italy showed that sugar beets sown in autumn were able to overwinter well and produce high yields. In the two study seasons, the lowest winter temperatures were −3,6°C and −6,3°C, respectively. Despite this, most beets sown at the end of October survived the winter.

In the Italian trials, conducted without irrigation, the best-performing sugar beet varieties sown in autumn yielded 80–85 t/ha of roots.