Vegetative growth and freezing tolerance of white clover (Trifolium repens L.) genotypes from Svalbard

Vegetative growth and freezing tolerance of two genotypes of white clover (Trifolium repens L.) collected at Svalbard (latitude 78degrees39' N. longitude 16degrees23' E) were studied in a daylight phytotron at controlled temperature and humidity. For comparison, two genotypes of a new Norwegian cultivar, Norstar, and one genotype of the cultivar AberHerald were included in the experiments. The genotypes from Svalbard gave higher dry-matter yields than the genotypes of Norstar, and one of them also exceeded the AberHerald genotype in dry-matter production at the temperatures studied, constant 12degreesC and alternating 15/9degreesC and 12/6degreesC (12/12 h). The genotypes from Svalbard were more tolerant of freezing than all the other genotypes. After a successive hardening treatment at 6degreesC and 0.5degreesC they obtained LT50 values (temperature for 50% survival) of - 16degreesC. The origin of these genotypes is not known, but their high productivity and freezing tolerance may make them useful for further breeding of white clover for marginal conditions.