Variation and probability grading of quantitative characters of traditional chrysanthemum cultivars

Identification and classification of cultivated plants is fundamental to the protection and application of plant varieties. Chrysanthemum × morifolium Ramat. is a cultivar with abundant variations, and rational grading of its quantitative characters may help us evaluate the cultivar resources from the quantitative and standard perspectives, and establish more detailed evaluation standards for the chrysanthemum. In this study, we tested and analyzed the variation of the 18 quantitative characters in 400 large-flowered chrysanthemums. The result showed that coefficients of variation of the 18 quantitative characters were all above 15%. Among them, the coefficients of variation were high in the number of disc florets (101.85%) and ray florets (70.02%), and floret width (59.49%), suggesting that some of flower traits have abundant genetic variation. The K-S test results indicated that 13 characters conformed to the normal distribution, whereas the other 5 characters followed skewed distribution. The values of 13 normally distributed characters could be divided, in a unified way, into 5 grades by 4 dividing points. The grading criteria of the other 5 characters were calculated. By applying the probability grading method of the new classification standards, the 400 chrysanthemum varieties are assigned and merged into digital codes. Through comparative analysis of these digital codes, we found that nine quantitative characters can distinguish 400 varieties. The assignment of these 400 cultivars according to the probability grading criteria can differentiate all the cultivars, and therefore, the new criteria of main ornamental characters could be regarded as the criteria of cultivars classification. The results of the probability grading would provide reference for the classification, identification and database construction.