Genetic variation of quercetin glucoside content in onion (Allium cepa L.)

Quercetin glucoside content was investigated in the various genetic resources of onion (Allium cepa L.). Quercetin glucoside content of long-day cultivars was higher than that of short-day cultivars. Among the long-day cultivars, Rijnsburger cultivars from North Europe and their close relatives had higher quercetin glucoside content than those of Hokkaido and North American origins. Quercetin glucosides were undetectable in all white cultivars. Red onions had a higher quercetin glucoside content than that of their closely related yellow onions. In the Hokkaido, North American and short-day cultivars, quercetin glucoside content, although low, had positive correlation with percent dry matters and bulb diameter. Hence, to breed cultivars with higher quercetin glucosides was considered possible. When this thesis was tested by crossing pollen parents with higher quecetin glucosides with a common seed parent, F-1 progenies with increased levels resulted. From these results, we Conclude that high quercetin cultivars can be bred by using Rijnsburger cultivars with high quercetin glucosides and moderate dry matter contents as parents. Furthermore, quercetin glucoside content had positive correlation with storage, i.e., the percent quercetin-3,4'-D-O-beta-diglucoside increased during storage. Some Rijnsburger cultivars showed high quercetin glucoside levels even though they had the same dry matter content as those from Hokkaido.