Capture and use of solar radiation, water, and nitrogen by sugar beet (Beta vulgaris L.).

Sugar beet is spring-sown for sugar production in most sugar beet-growing countries. It is grown as a vegetative crop and it accumulates yield (sugar) from very early in its growth cycle. As long as the sugar beet plants do not flower, the sugar accumulation period is indefinite and yield continues to increase. This paper reviews the success of the sugar beet crop in capturing and using solar radiation, water and mineral nitrogen resources. The prospects for improved resource capture and therefore increased sugar yield are also considered, particularly the potential to increase solar radiation interception in the future by sowing the crop in the autumn.

Genotypic variation for drought tolerance in Beta vulgaris.

Insufficient soil moisture during summer months is now the major cause of sugar beet yield losses in the UK. However, selection for increased drought tolerance has not been a breeding priority until recently. Genetic variation for drought tolerance is an essential prerequisite for the development of more stress-tolerant varieties, but commercial sugar beet varieties seem to have similar yield responses to drought. The objective of this study was to assess the degree of genotypic variation for drought tolerance within a wide range of sugar beet germplasm and genebank accessions within Beta. Thirty sugar beet genotypes were screened under field drought conditions, and putative drought tolerant and sensitive lines (in terms of yield reduction in polythene-covered vs. irrigated plots) were identified. Significant genotype x water treatment interactions were found for dry matter yield and relative leaf expansion rate. Genotypic differences for drought susceptibility index were also significant. Differential sensitivity of seedling shoot growth to water deficit was examined by comparing 350 genebank accessions in a simple growth chamber screen. Methods of data management were devised to highlight lines for entry into subsequent field tests. The results of the field and seedling screens indicate that there is variation for tolerance to water deficits within sugar beet and related types, and that there are lines that show greater drought tolerance than selected commercial varieties. Divergent lines showing contrasting behaviour should aid in the identification of key morpho-physiological traits that confer drought tolerance.