Analysis of karyotype diversity of 40 Chinese chrysanthemum cultivars
To investigate the genetic differences in Chinese large-flowered chrysanthemum (Chrysanthemum×morifolium Ramat.) cultivars, we selected 40 typical and stable cultivars on which to carry out cytological studies using karyotype analysis. The results showed that 67.5% of these cultivars were hexaploid-based aneuploid and that the proportion of hexaploid decreased with passing time. Moreover, 35% of the cultivars had 1–4 satellite chromosome(s). The probability of satellite chromosomes rose with increasing chromosome number. Most of the karyotypes were 2A and 2B. The probability of types 2A and 2C also increased with increasing ploidy of the cultivars. The mean of long-/short-arm ratio and the variation of long-/short-arm ratio were positively correlated (r2 = 0.72). There was no obvious difference in the asymmetry coefficient of karyotypes, but the discrepancy in the variance of karyotype asymmetry index and relative length of chromosomes was quite distinct. In terms of karyotype parameters, the petal types of chrysanthemums were classified to five groups as flat, tubular, spoon, abnormal, and anemone. We did not observe any obvious orderliness among flower head types. Considering the relationship between karyotype parameters and phenotypic characters, variation of long-/short-arm ratio and asymmetry coefficient of karyotypes had the greatest relevance toward most phenotypic characters. The above results indicate that karyotype parameters possess great values for cultivar identification, classification, and genetic analysis in chrysanthemums.