Changes in non-structural carbohydrate composition during bulbing in sweetand high-solid onions in field experiments

The composition of non-structural carbohydrate (NSC) content of predominant ly long-day onion germplasm has been assessed over several years and in a b i-location trial. It was observed that genetic rather than environmental fa ctors determined the NSC composition of onion bulbs. Glucose was the NSC co mponent which was most closely correlated with genotype. Fructose was the o nly NSC component that was significantly affected by environment. Sucrose a nd 1-kestose (DP3 fructans) were not correlated to a large extent to the ot her NSC components, indicating their transient role in the fructan metaboli sm. Strong negative correlations were observed between reducing sugars (i.e . fructose and glucose) and dry matter content (DM). Furthermore, it was sh own that accessions differed significantly in their fructan accumulation pa ttern: high DM accessions showed accumulation of fructans over the whole bu lbing period, whereas. low DM accessions quickly reached a plateau. Implica tions for the breeding of high quality onions are discussed. (C) 2001 Elsev ier Science B.V. All rights reserved.