Phenotype related differences in frost tolerance of winter sugar beet (Beta vulgaris L.)

The cultivation of sugar beet as a winter crop might improve its economic performance by extending the sugar factories' processing campaign and/or increasing the taproot yield. Adequate frost tolerance is one major prerequisite for successfully cultivating winter sugar beet under Central European climate conditions. Among others, phenotypic plant properties such as taproot size before winter are known to have a strong effect on overwintering success. The aim of our study was to comprehensively evaluate the influence of plant phenotype in relation to winterly weather conditions on frost tolerance and crop survival. Therefore, a series of field trials was conducted at different environments, each having different sowing dates (April, June, August) and plant densities (148, 246,370 thousand plants ha(-1)) to generate high phenotypic variation. Frost tolerance mainly depended on the winter conditions, with the minimum air temperature and the presence of a protecting snow or straw cover during frost periods being crucial. Moreover, the frost tolerance was highly dependent on the plant size measured by the taproot diameter, with highest survival rates at ca. 1-2.5 cm; the optimum size appeared to be independent from plant age (sowing date). Optimal sized plants were most frequently obtained from sowing in August. Such plants tolerated freezing events of the taproot tissue down to ca. -4.5 degrees C (air temperatures down to ca. -15 and at least -21 degrees C for bare and covered crops, respectively), while larger taproots got frost damaged at ca. -1.5 degrees C. Higher taproot tissue concentrations of the solutes K, Na, amino N, but not sugar, contributed to the higher frost tolerance of optimal sized sugar beets. Moreover, a lower amount of extracellular water in taproot tissue was likely to explain the differences.(C) 2013 Elsevier B.V. All rights reserved.