Abstract:

Tree peonies, native to China, are widely cultivated in many countries, but the threat of genetic degradation in new varieties is serious due to the selection of local cultivars as parents in breeding. Hence, it is important to use introduced cultivars from different origins when breeding new varieties. To assist in enlarging the genetic basis of tree peonies, we examined 41 morphological traits of 68 introduced tree peony cultivars from the USA, France and Japan, and compared them to 21 local varieties. We found high levels of morphological diversity among cultivars; coefficients of variation based on morphological traits ranged from 14.3% to 159%, with an average of 44.5%. A principal component analysis (PCA) integrated these 41 traits into 10 principal components. Among these components, 7 were most strongly associated with the first factor, representing flower characters; the other 3 were associated with the second factor, representing leaf characters. Results of a cluster analysis concurred with those of the PCA analysis. All cultivars clustered into two groups: the first was characterized by those that exhibited non-leaf-chromatic, larger flower diameter, non-petal-blotch, late flower time and erect flowers, and most of them were foreign cultivars; the second included foreign and Chinese cultivars and can be further classified, and was characterized by non-leaf-chro- matic and small flower diameter. Moreover, the cluster analysis showed that most foreign cultivars were well-differentiated from domestic cultivars morphologically.

Key words: tree peony, introduced cultivars, breeding, genetic variation, morphological diversity, cluster analysis