Autumn sown sugar beets (winter beets) are expected to yield markedly higher
than spring sown beets. This requires a continuous growth during an extended
growing period. So far, bolting-resistant sugar beet varieties are not available to
test winter beets under field conditions in Central Europe. The objective of this
study was therefore to analyse yield formation and sugar storage of sugar beet
plants during an extended growing period to estimate whether sugar beet has the
potential to generate the theoretically expected yield increase. From 2008 to 2012,
pot experiments were carried out in the glasshouse with 11 sowing dates spread
over the years with sequential harvests. The oldest plants were grown for 859 days
(14 242 °Cd). Root fresh matter yield continuously increased till the latest harvest.
In contrast, the sugar concentration reached an optimum value between
3400 and 5000 °Cd and then decreased with time. Despite longer growing periods,
the number of cambium rings, which are regarded as essential for sugar storage,
did not change. This points to an early and genetically fixed determination
of the formation of cambium rings. Additionally, the rate of photosynthesis
decreased concomitantly with the sugar concentration. In conclusion, there is
some evidence that the sugar concentration of the storage root is limited by the
sink capacity, which in turn controls the source activity by a feedback regulation
of photosynthesis and leaf formation. The dry matter composition of the storage
root changed towards lower sugar concentration and concurrent higher concentration
of cell wall compounds (marc). The sugar yield still increased beyond a
thermal time at which winter beets will probably be harvested in practice. Hence,
the theoretical yield increase in autumn sown sugar beets can be realized, provided
that the plants show sufficient winter hardiness and bolting resistance.