Classification Of Chaenomeles Cltivars

The genus Chaenomeles Lindley is assigned to the subfamily of the ecologicaily and economically important Rosaceae. Four species, C. cathayensis (Hemsl.) Schneider, C. thibetica Yü, C. speciosa (Sweet) Nakai, and C. japonica (Thunb.) Lindley ex Spach. are now recognized in Chaenomeles. C. japonica is native only in Japan, C. cathayensis, C. thibetica, and C. speciosa are mainly distributed in south-western, middle and eastern of China. The showy flowers of Chaenomeles occur in clusters, and open in the early spring. Fruits become fragrant during ripening in autumn. Chaenomeles species are the important ornamental flowers, herbs and fruits, which are cultivated widely throughout the world. Individual species exhibit a strong plasticity of form and easy interspecific hybridization which is value in commercial horticulture but of difficulty to botanists. With the new cultivars bred and types of variation investigated, there occur synonyms and homonym phenomena. The botanical source and relationship of Chaenomeles cultivars are unclear and the lack of proper cultivar classification needs further taxonomic research.Based on the survey of Chaenomeles cultivars resources, the numerical taxonomic method was used for the cluster analysis of 29 cultivars and 2 wild species with 41 morphological characters. The result revealed that 31 OTUs (Operational Taxonomic Units) could be divided into 4 phenetic groups according to their botanical sources, namely C. cathayensis system, C. thibetica, C. speciosa system and C. japonica system. C. japonica system and C. cathayensis system are the most distantly related systems; C. thibetica appeared to be rather closely related to C. cathayensis; C. speciosa system together with the hybrid taxon C.×superba and C.×vilmoriniana takes an intermediate position between C. japonica system and C. cathayensis system. Principal component analysis showed that the 41 characters can be consolidated for the 6 principal components and their accumulative contribution ratio amounted to 72.396%. Integrated cluster analysis and principal component analysis with practical applications , the author suggested that the classification of Chaenomeles cultivars should be firstly based on the systematics of wild species (cultivar sources). Then, the flower size could be as the second criterion for the classification of Chaenomeles cultivars, and the flower color as the third criterion.The purpose of this paper is intended to establish SRAP reaction system in Chaenomeles species. Simplified SDS method was used to extract the genomic DNA from the silica gel dried young leaves. The factors which affect the SRAP amplification, such as Mg2+ concentration and template DNAs concentration, were optimized. Efficient SRAP reaction systems were developed as follows: the reactions were performed in a volume of 25μL containing 1×PCR Buffer, 2.0 mmol·L-1 Mg2+, 0.2 mmol·L-1 dNTPs, 1.0 U Taq DNA polymerase, 10 pmol primers, and 50 ng template DNAs. Using the optimum system, 22 pairs of SRAP primers, with high stability and polymorphism had been obtained. The reaction system in this study is suitable for SRAP research of Chaenomeles species, and it has set up a foundation for species germplasm identification and genetic map construction.The botanical source, genetic relationship, and genetic diversity of Chaenomeles cultivars were probed. The arm is to provide a scientific basis for Chaenomeles cultivars classification. The cluster analysis, principal coordinate analysis and genetic diversity of 27 cultivars of Chaenomeles and 5 wild species were analyzed using 22 SRAP primer combinations. A total of 152 polymorphic loci were detected among these materials with average 6.91 polymorphic loci per SRAP primer combinations, and the percentage of polymorphic loci was 73.08%. The cluster analysis result revealed 32 materials could be divided into 4 groups, namely C. cathayensis system, C. thibetica, C. speciosa system and C. japonica system. C. thibetica appeared to be rather closely related to C. cathayensis system. C. japonica system and C. speciosa system clustered into together. C. japonica system and C. cathayensis system were the most distantly related systems. C. speciosa system took an intermediate position between C. japonica system and C. cathayensis system. Genetic diversity analysis showed that C. japonica system and C. speciosa system were more diverse than C. cathayensis system. Differences in mating and breeding systems among the species can be suggested as a possible explanation of the results. In the genus level, the coefficient of genetic differentiation among species (GST) was 0.4969. SRAP molecular markers were an effective research tool for genetic relationship of Chaenomeles cultivars. Integrated morphological characters and SRAP analysis, the state of style hairiness basally was one of accurate indicators which identified the botanical source of Chaenomeles cultivars. C.×superba was a non-independent taxon, and could be used as a cultivar group in C. speciosa.