Description and classification of a white clover (Trifolium repens L.) germplasm collection from southwest Europe

Abstract

A collection of 128 populations of white clover from southwest Europe was grown as spaced plants and compared with a range of bred cultivars for shoot morphology, spring and summer growth, flowering, leaf marks, cyanogenesis, persistence, and susceptibility to stem nematode (Ditylenchus dipsaci). Collected populations were grouped by latitude and altitude of origin. Cyanogenesis (% and score), V leaf mark (%), leaf size, early-flowering (%), flower abundance, and spring growth declined with increasing latitude and altitude. Factor analysis was used to reduce the number of variables before populations and cultivars were clustered, using the flexible beta method, into six groups. Lines in the cluster that contained medium and large-leaved New Zealand cultivars were highly productive and persistent, with high cyanogenesis levels, very dense foliage, and abundant flowers. Another cluster contained the ladino cultivars and collections that had low cyanogenesis levels, large leaves, upright habit, poor spring growth, good persistence, low nematode damage, and were late-flowering. A large number of the collected populations fell into a cluster characterised by small leaves, prostrate habit, and low productivity. Another large cluster contained mainly Mediterranean lines that were very early-flowering, very highly cyanogenic, large-leaved, and semi-prostrate, with excellent spring growth but poor summer growth. The largest cluster contained the small-leaved productive cultivars and collected populations which were moderately cyanogenic but sustained high nematode damage. Lines in the smallest cluster were characterised by a high incidence of V^y leaf mark and relatively high leaf density. The clustering was compared with geographic groupings of populations. Geographic groups were phenotypically heterogeneous, over the total range of characters used, with populations from the same region often occurring in several clusters. Road-side collections probably because of their close relationship with adjacent pasture populations, occurred in several clusters and did not form an identifiable phenotypic group representing permanent, ecologically separate populations. Compared with a previous cluster analysis of a world collection of white clover cultivars, the southern Europe collection contained a group of very small-leaved, prostrate, non-productive populations that differed from any cultivar grouping because such types are not in commercial use. Clustering analyses of the type undertaken here assist the use of new germplasm in plant improvement programmes by identifying phenotypically similar accessions and thereby reducing the number of lines to be evaluated.

Keywords:

• white clover
• variation
• morphology
• cyanogenesis
• flowering
• leaf markings
• classification
• cultivars
• populations
• multivariate analysis