Flower Color and Anthocyanidin Pigment Profiles of the Phlox Collection in the National Plant Germplasm System
Application Technology Research Unit
Project Number: 5082-21000-017-06
Specific Cooperative Agreement
Start Date: Sep 11, 2013
End Date: Jul 31, 2014
The importance of phlox as an ornamental plant for the nursery and floriculture industry, and the need to establish a germplasm collection of this genus, led the Herbaceous Ornamental Crop Germplasm Committee to make it a priority for the OPGC. The genus is native to North America, consisting of about 60+ species distributed throughout the continent although only a handful of the species from the Eastern and South-Central regions have been domesticated and are cultivated widely. The signature feature of phlox cultivars is the profuse and vibrantly colored flowers; the majority of cultivars have been selected for unique colors. Novel flower patterns are constantly being sought, particularly in the range of colors not typical of the crop; for phlox, rare colors such as yellow and orange have been reported only in select genotypes of one or two pecies (Phlox nana and P. drummondii). The potential for new color combinations in different species of phlox may be achieved by interspecific hybridization of appropriately chosen parents. As part of a broad effort to develop and characterize a comprehensive germplasm collection of this genus, we are exploring ways to assess important characteristics such as resistance to powdery mildew (and other foliar diseases), environmental adaptability, fragrance, duration/extent of flowering and, for the purpose of this agreement, flower colors. Since 2010 the OPGC has been developing a phlox collection that now consists of over 400 accessions; the majority of these (about 70%) are of wild origin with the rest representing diverse cultivars used for comparisons and reference. While many challenges remain in the production of phlox seed for long-term storage, we are pursuing a strategy of simultaneous seed increases and evaluation/characterization of the collection. One of our goals is to describe the variation in flower color among wild-collected accessions. Preliminary observations of the collection indicate subtle variation in color among the accessions; the dominant colors vary by species but they can be broadly described as pink, lavender/lilac, pale-blue, white or magenta. We would like to quantify the color variation among accessions using digital imaging, but also evaluate the anthocyanin and anthocyanidin profiles associated with each accession, particularly those that do not show obvious color differences. We hypothesize that pigment variation may be greater than color variation and that identifying accessions with unique profiles may provide potentially more interesting parents to use in hybridization. The in vivo flower color initially determined by unique chemical modifications of anthocyanins is significantly affected by other factors such as those that influence vacuolar pH (Yoshida et al., 1995), the presence of copigments (Forkmann, 1991), and the formation of anthocyanic vacuolar inclusions (Markham et al., 2000). It is not known to what extent these factors play a role in Phlox flower color, but establishing baseline information about colors and pigments will assist in understanding this important ornamental trait in the crop.
We have approximately 240 wild-collected accessions of Phlox. A subset of these will be used for assessing flower color by digital imaging. Five flowers per plant of up to 5 individuals within each accession will be evaluated for flower color using a scanned digital image. The plants will be chosen to represent the range of colors noticed in the accession. For accessions with no observable color variation among the population (e.g. P. bifida), one representative plant will be selected for the initial color. Computer-based analysis of digital images has been used to objectively characterize morphological variation found in plants, including shape and color of leaves, flowers, and fruit (Lootens et al., 2007; Yoshioka et al., 2006). Tomato AnalyzerTM (TA) is a free software initially developed for rapid, high volume analysis of tomato fruit morphology using digital images generated with flat-bed scanners; a color test tool (TACT) has also been developed that allows for accurate quantification of color and color uniformity (Darrigues et al., 2008).To examine the anthocyanin/anthocyanidin composition of phlox flowers, we propose to initially survey a representative sample of accessions from the species with greater commercial value (P. carolina, P. divaricata, P. drummondii, P. glaberrima, P. maculata, P. paniculata, P. stolonifera, and P. subulata); these represent 128 accessions. We will select 3-5 accessions from each species representing a distinct range of flower colors for the species.