Effects of adaptation to winter stress on biomass production, growth and morphology of three contrasting white clover cultivars

Changes in biomass production and partitioning, together with morphology and growth of three white clover (Trifolium repens L.) cultivars after exposure to winter stress were recorded in a controlled environment study. The cultivars used were Grasslands Huia (H. New Zealand), AberHerald (AH. bred in UK from material of Swiss origin) and Sandra (S, Sweden), sub-populations of these (survival populations), and a wild ecotype from the Uppsala area. The sub-populations Here collected after 2 (with the exception of S) and 4 years of winter stress, respectively, at Uppsala (59 degrees 49' N, 17 degrees 39' E). In the controlled environment study the photoperiod was 12 h and there were two temperature regimes, namely 23/18 and 12/9 degrees C (day/night), respectively. The experimental plants were cloned from eight different plants of each population. There were few interactions between populations and temperature regimes. Biomass production was lowest in the Swedish populations and in the surviving populations of the other cultivars collected after 4 years of exposure to winter stress. However, biomass partitioning, with the exception of allocation to branches, remained unaffected. Morphology differed significantly between cultivars, but, with the exception of internode length, was unaffected by exposure to winter stress. Internode length, was significantly reduced in surviving populations of both H and AH after exposure to four winters, when its value was similar to that of the Swedish populations. The reduced internode length was a result of a greater reduction in the stolen extension rate than in the leaf appearance rate of survival populations compared with the original populations. It is hypothesised that reduced internode length would hale implications for the carbon economy of the plant.