Fatty acid and sugar content in white clover in relation to frost tolerance and ice-encasement tolerance

Physiological characters relating to winter survival were measured in stolo ns of three white clover Populations. Plants were grown in pots and hardene d naturally outside in Iceland (66 degreesN); samples were taken on three o ccasions from autumn to spring. The cultivar AberHerald was compared with a population that had survived one winter in experimental plots in southern Iceland (AberHerald selected) and an indigenous population from Norway (HoK v9238). Frost tolerance and ice-encasement tolerance were determined in the laboratory using meristematic stolon cuttings, and the temperature and num ber of days required to kill 50 % of the population were calculated. Fatty acid and sugar contents of stolons were measured in the same material. The Norwegian population HoKv9238 was much more winter-hardy than the AberHeral d populations and its stolons had a higher dry matter percentage. Total amo unts of unsaturated fatty acids were higher in HoKv9238 than in AberHerald populations, with differences being most prominent for the 18:2 fatty acid. In September, the starch content was significantly higher in stolons of Ho Kv9238 than in those of the two AberHerald populations, but by January the starch content had decreased drastically, especially in HoKv9238. Sucrose w as the most abundant water-soluble carbohydrate: in September. populations had similar sucrose contents but levels had decreased by January in AberHer ald populations but not in HoKv9238. Comparison of the two AberHerald popul ations showed that the selected population was more frost- and ice-encaseme nt tolerant than the original population in autumn. This coincided with hig her levels of the 18:2 fatty acid. (C) 2001 Annals of Botany Company.