Seasonal variation of morphological characters and growth in contrasting white clover populations

The seasonal growth potential of contrasting white clover populations differing in leaf size and geographical origin was studied during the year in a cool glasshouse in the absence of freeze damage. A Mediterranean population showed superior growth to all other populations during the cooler months of late autumn, winter and spring when it also had longer leaflets, petioles and internodes. In contrast, large leaf types of north European origin grew faster and had longer leaflets, petioles and internodes than the Mediterranean type during summer. A hybrid between these contrasting types showed an intermediate response with more uniform growth and expression of these morphological characters throughout the year. The exploitation of this out-of-season growth potential by hybridisation of Mediterranean and north European genotypes followed by selection is discussed in the context of recent introductions of ecotypes from the Swiss Alps in which desirable combinations of good spring growth and winter hardiness have been identified.