Variation in the low temperature growth and frost tolerance of natural genotypes of Trifolium repens L. from Britain and Norway

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Abstract
Summary: Sixty-two genotypes of Trifolium repens (white clover) collected from latitudes 52° to 68° N and five selected genotypes of the cultivar S.184 were screened for shoot growth at low temperature and short daylengths in a controlled environment cabinet and in the field, and subjected to cold hardiness treatments ranging from – 2·5 to – 14·0 °C.Considerable variation was discovered in several of the growth characteristics and in the frost tolerance of the genotypes. Genotypes exhibiting the highest rates of stolon extension were found in the more southerly latitudes. A high proportion of leaves produced during winter on the primary stolons of the selected cultivar plants subsequently died during the late spring at the upland field site, but several of the naturally occurring genotypes were able to retain more leaves per stolon in spring. Some genotypes appeared to maintain either short or long internodes throughout the spring in the field, whilst others produced relatively short internodes in early spring and long internodes later in the season, and vice versa. Only a small percentage of the genotypes possessed relatively long leaflets. A correlation was found between maximum leaflet length of the genotypes in early spring, and maximum leaflet length in late spring.No relationship was found between frost tolerance and the growth of plants at low temperature. Frost sensitive and tolerant genotypes were found throughout the latitudinal and altitudinal ranges studied. Exposure to prevailing winds and possibly snow cover at the site of origin appeared to be important factors associated with the frost tolerance of T. repens plants.