Intraspecific variation for frost hardiness in white clover

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Abstract
Summary: The frost hardiness of 5-month-old seedlings of 12 white clover cultivars was examined at – 4, – 8, – 12 and – 16°C and in a subsequent study the frost hardiness of 6-month-old seedlings of 190 experimental lines and 23 cultivars and ecotypes was determined at – 12°C. There were large differences among cultivars and lines in frost tolerance based on the percentage of plants damaged and the percentage of leaves killed. The most frost-hardy were the cultivars Podkowa and Undrom and ecotypes collected from Kaikoura and Nelson Lakes. There was no significant, correlation between the percentage germination of cultivars at 4 °C and their subsequent frost hardiness.Large-leaved, erect cultivars tended to be more frost sensitive than small-leaved, prostrate cultivars. Frost-tolerant cultivars and lines tended to be acyanogenic. Selection for low winter growth did not increase frost tolerance. However, lines derived from crosses between genotypes of cold-hardy lines selected for rapid germination at 4 °C were more frost-hardy than lines from genotypes selected in a similar way that had been crossed with unselected Huia genotypes.