Genome size estimations in Chrysanthemum and correlations with molecular phylogenies

Abstract

A wide range of ploidy variation exists among native Chinese Chrysanthemum germplasm. This study examined the evolution of genome size, Cx value, and chromosome number in Chinese Chrysanthemum within a phylogenetic context. The genome size of 15 species belonging to Chrysanthemum and three related genera was determined using flow cytometry. Nuclear ribosomal ITS and chloroplast trnL-F intergenic spacer sequence were used to construct molecular phylogenetic trees. Genome size values among the 15 species divide into three discrete groups, which positively correlate with three ploidy levels. We found significantly and negatively correlated 1Cx values to ploidy levels in all 15 species and a genome downsizing after polyploidization effect in Chrysanthemum. Two major phylogenetic clade, the C. indicum group and the C. zawadskii + Ajania group, possess significant differences in genome size and 1Cx values. The genome size and 1Cx values in the C. indicum group were significantly lower than in the C. zawadskii group, even though both have same ploidy level, and significant latitude and morphology correlations can be inferred. Diploid Chrysanthemum species similar in 1Cx values to C. indicum (Mt.Tianzhu) and C. indicum (Fujian) indicate that some populations of tetraploid C. indicum originated by autoploidy. We deduced that C. chanetii is a relatively young species, C. vestitum relative ancient and that the divergence between Chrysanthemum and Ajania may have been relatively recent, presumably the same divergence as created C. zawadskii.