Frost de-acclimation of barley (Hordeum vulgare L.) and meadow fescue (Festuca pratensis Huds.). Relationship between soluble carbohydrate content and resistance to frost and the fungal pathogen Bipolaris sorokiniana (Sacc.) Shoem.

Plants of barley (Hordeum vulgare) and meadow fescue (Festuca pratensis), two species differing in their susceptibility to the fungal pathogen Bipolaris sorokiniana, were cold-acclimated. Changes in frost resistance, susceptibility to B. sorokiniana, osmotic potential, water content, and composition of low molecular weight sugars were studied in leaves over a period of 14 d during subsequent de-acclimation. Cold acclimation promoted resistance to frost and the fungal pathogen in both species. Plants subjected to de-acclimation lost their ability to withstand frost after about 24 h, but retained enhanced levels of resistance to the pathogen. This effect lasted longer in the less pathogen-resistant barley than in meadow fescue. Changes in osmotic potential observed after cold-acclimation and during dehardening were correlated with changes in frost resistance, but not with changes in susceptibility to the pathogen. The same applied to changes in the low molecular weight sugar content in leaves of meadow fescue. In barley, cold-acclimation induced alterations in osmotic potential and the subsequent increase in frost resistance was not correlated with variation in soluble carbohydrate contents. The results indicate that cold-acclimation induced changes in leaf water potential and that soluble sugar content is not involved directly in the increased resistance to the pathogen which was observed after cold acclimation. (C) 2000 Annals of Botany Company.