Quantitative Classification of the Morphological Traits of Ray Florets in Large-flowered Chrysanthemum

Abstract

<jats:p>The large-flowered Chinese chrysanthemum is one of the most morphologically complex ornamental plants, and its identification and classification requires a well-defined and reproducible system. The diversity of the capitulum is determined mainly by multiple shapes of ray florets. However, the existing classification systems for ray floret types are incomplete and unsystematic. In this study, 299 ray florets from 151 large-flowered chrysanthemum varieties in China, as well as 12 related traits of ray florets, were selected for quantitative classification. First, as one of the most important indices of ray floret shape, the corolla tube merged degree (CTMD) was defined as the corolla tube length/ray floret length (CTL/RFL). Combined with a probability grading method and linear regression analysis, the CTMD was divided into three groups, flat, spoon, and tubular, of which the CTL/RFL ranged from 0 to 0.20, 0.20 to 0.60, and 0.60 to 1.00, respectively. Second, Q-mode cluster analysis indicated that each group could be further categorized into three types (straight, curved, and atypical), based on other important variables in the ray floret. Finally, the ray floret was classified into nine types, including flat-straight, flat-curve, flat-atypical, spoon-straight, spoon-curve, spoon-atypical, tubular-straight, tubular-curve, and tubular-atypical. This ray floret classification system will be valuable in the classification of capitulum shape and has significance for the identification, breeding, and international standardization of chrysanthemum cultivars.</jats:p>

High-density genetic map construction and identification of loci controlling flower-type traits in Chrysanthemum (Chrysanthemum × morifolium Ramat.)

“…7b). The detailed measurement methods and the analysis of phenotypic traits are described in Song et al 2 .…”

“…Flower type is an important quality trait of all ornamental plants 1,2 . Flower-type variation is extremely abundant in chrysanthemum due to the presence of ray and disc florets with complex and varied shapes in the chrysanthemum capitulum.…”

CmBES1 is a regulator of boundary formation in chrysanthemum ray florets

“…To further study the changes in the degree of merging of the outermost ray florets, 15 of the outermost ray florets from each inflorescence of 15 individual plants were randomly selected from each transgenic line to measure the degree of ray floret fusion. The chrysanthemum ray floret shape can be flat, spoon shaped, or tubular, with the CTMD ranging from 0 to 0.2 (flat), 0.2 to 0.6 (spoon shaped), and 0.6 to 1.0 (tubular) 22 . Among the WT chrysanthemum plants, 77.0% of the total number of the outermost ray florets were flat, and 23.0% were spoon shaped; there were no tubular outermost ray florets (Fig.…”

“…The outermost ray florets at the open-flower stage of WT and CmBES1 transgenic chrysanthemum plants were used to measure the CTMD, which was defined as the corolla tube length/ray floret length and measured as described previously 22 . The main characteristics compared between the ray florets and disc florets are listed in Supplementary Table S5.…”

“…The ray florets are bilaterally symmetrical, with two dorsal petals that are degenerated and three fused petals that form an elongated ventral ligule, while the disc florets are radially symmetrical with five equal petals 21 . The shape of the ray floret is important for the chrysanthemum flower type and can be classified as flat, spoon, or tubular according to the degree of corolla tube merging (CTMD), which ranges from 0 to 0.2, 0.2 to 0.6, and 0.6 to 1.0 22 .…”