SOLUBLE SUGARS AND WINTER HARDINESS IN FLOWER BUDS OF FORSYTHIA SPECIES

Abstract

Little is known about the biochemical factors responsible for the wide range in flower bud hardiness of Forsythia species. In other genera, a correlation has been reported between soluble sugars, particularly raffinose and stachyose, and hardiness. Total starch and soluble sugars, their relationship to flower bud hardiness and levels of individual sugars were studied in four Forsythia species: F. × intermedia `Spectabilis', F. × intermedia `Lynwood', F. suspensa var. fortunei and F. `Meadowlark'. Hardiness was determined either by sampling flower buds at intervals during controlled freezing tests or by thermal analysis. Total sugars were extracted with water/ethanol and quantified with Anthrone. Individual sugars were separated and quantified with high pressure liquid chromatography. `Lynwood', the least hardy of the four cultivars, was killed by -16C, while `Spectabilis, the most hardy, survived -22C in midwinter. Total sugars accumulated throughout the winter in buds, apparently at the expense of total starch, in F. `Meadowlark' and F. suspensa var fortunei. As total sugars accumulated in `Spectabilis', however, total starch increased slightly. Although fructose, glucose, galactose and melibiose were detected throughout the year, raffinose and stachyose, were detected only in hardy flower buds.