Dispersal Principles of Sugar Beet from Seed to Sugar with Particular Relation to Genetically Modified Varieties

Autor/in: Märländer, B., T. Lange, A. Wulkow
Jahr: 2011
Zeitschrift: Journal für Kulturpflanzen 63
Seite/n: 349-373
Stichworte: Verbreitungsgebiete Saatgutvermehrung Saatgutaufbereitung Einkreuzung Auskreuzung Pollenübertragung kleine Rüben Rübenrückstände „geschlossene Systeme“ distribution areas seed propagation seed processing incross outcross pollen transfer small beets beet residues closed system

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Abstract

The taxon Beta comprises different cultivated and wild beet species assigned to three genepools in relation to their crossability. In Europe, the distribution area of wild beet is limited to a few mountainous and coastal sites, and Beta vulgaris ssp. maritima L. Arcang. is the only wild beet species of importance in sugar beet cultivation/ multiplication areas. In Germany it can be found on Helgoland Island and at coastal sites between Fehmarn Island and Kiel. In 2010, sugar beet was cultivated on roughly 1.5 million ha in Europe, 380,000 ha of which were in Germany (WVZ 2010). Basic and certified seed are solely produced and processed in the favourable climate of a few regions in northern Italy and southern France, whereas pre-basic seed is exclusively produced in the immediate vicinity of a few breeding stations in Europe. The seed companies are solely responsible for seed production and processing and place great emphasis on relevant management. Hybrid variety seed is produced via stecklings, which are planted in rows to ensure pollen transfer from the male fertile pollinator to the male sterile maternal line. For four weeks during flowering, pollen can be transported over a distance of > 500 m by wind. To prevent seed contamination by cross-pollination, seed production is spatially separated from sugar beet growing areas and wild beet habitats. After harvest, the seed is delivered without losses in sealed containers first to regionally and later centrally located seed processing stations. After processing, the seed is marketed in sealed packages. The pelleted seed is placed precisely into the prepared seed bed and covered with soil. Seed dispersal is rare, but can occur within areas susceptible to water erosion. Such erosion can be avoided by mulching. Seeds split open by mice are incapable of germination because the endosperm is eaten. About 90% of seeds capable of germination (germination capacity in the laboratory about 95%) emerge. Seeds that do not emerge are not viable under the respective environmental conditions in the field.1 Sugar beet are biennial plants forming a beet in their first season. If the beets are not harvested, flowering shoots appear in the second year after vernalisation. However, the formation of flowering shoots (bolters) in the first year is possible (probability < 0.05%) owing to the genetic constitution of the plants and/or certain weather conditions. The flowers of bolters from hybrid varieties are semi-fertile, that is the seed set is lower than that of bolters from formerly grown, fully fertile varieties. Cross-pollination from cultivated beet to wild beet populations and vice versa requires spatially overlapping populations, synchronous flowering periods as well as adequate wind strength, wind direction and low air humidity. Because of the different flowering periods of cultivated and wild beet, their populations maintain their genetic divergence. A gene flow from cultivated beet to wild beet populations can be prevented through spatial separation of sugar beet cultivation. Annual bastards result from crosses between wild beets, annual bolting cultivated beets and flowering seed beets. Because they flower earlier, they are more crucial in terms of gene flow than bolters from hybrid varieties that flower later. Bolting sugar beets as well as bastards are of minor agronomic value and, therefore, usually eliminated by hand, mechanically or partly by selective herbicides. If such bolters are not removed, they develop seeds and establish a seed bank, becoming a permanent reservoir for germinating weed beets. The sugar beet root consists of two parts: the beet comprising the root, hypocotyl and lower compressed stem with dead petioles; and the crown, which is the upper compressed stem with living petioles. The upper part of the stem is potentially capable of regeneration. During harvesting, the beets are topped mechanically, but not in an optimal way for each beet. Losses of small beets and crowns of low topped beets that are capable of regeneration can be reduced by the adjustment of working speeds and lifters to the harvesting conditions. However, a certain proportion of crowns and small beets that are more or less capable of regeneration remain in the field, which are either buried through grubbing or ploughing during the sowing of the following crop or remain on the surface through mulching. Such remains are a good feed for wild boars, wild geese and others. Small beets or beet parts that survive over winter can completely be controlled by agronomic measures in the following crop. Damage caused by game animals can also occur during the vegetation period but, in general, the upper compressed stem with living petioles that is capable of regeneration is eaten preferentially. Immediately after the harvest, the beets are delivered to the sugar factory or stored temporarily in clamps at the field margin. Proper loading and locking of the goods to be conveyed as well as the correct return of lost beets and beet parts during loading effectively prevent the dispersal of plant material potentially capable of regeneration. In the sugar factory, the beets are cleaned in the beet washing house – either immediately or after temporary storage – and subsequently extracted at high temperatures. Cleaned leaf remains or small beet parts are incapable of regeneration and are either sold as animal feed together with pressed pulp or fermented in biogas plants in the sugar factory. Washed soil tare is stored for about three years and returned to the field or used for other purposes. Therefore, the sugar factory is a „closed system“, in which all plant parts capable of regeneration are degenerated, products are sold and residual material is recycled. Besides sugar production, sugar and fodder beets are used as a substrate for biogas plants.

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