In the words of Alain Meilland in the foreword of the Encyclopedia of Rose Science: “no other flower is as universally loved and grown or has a more illustrious history than the rose” (Meilland, 2003). Rose is a member of one of the most important horticultural families, the rose family (Rosaceae) and is admired for its great diversity of floral and plant characteristics. Sales of roses in 2014 in the United States generated $203.5 million from the production of 36.6 million plants by 1808 growers (U.S. Department of Agriculture, 2015). According to the Green Industry Research Consortium National Survey, roses accounted for 3% of overall sales from 18 different horticultural production crop categories of the industry worth $25.9 billion. Rose industry sales equate to contributions to the U.S. economy of ≈$777 million. Most roses (65%) are sold through retail outlets, with the remaining 35% of rose sales coming from landscape services (Green Industry Research Consortium, 2013). In North America, the economic impact of landscape roses in Canada was estimated at $149 million, and the value in the United States was estimated at $928 million (Vineland Research and Innovation Centre, 2013). The rose industry has a large economic impact worldwide.
Rose has four subgenera, more than 100 species (diploid through decaploid) and more than 30,000 commercial cultivars (mostly diploid, triploid, and tetraploid). These cultivars exhibit wide interspecific and intraspecific cross compatibility (Blechert and Debener, 2005; Byrne and Crane, 2003; Cairns, 2000; Jian et al., 2010; Spiller et al., 2011; Ueckert et al., 2015; Zlesak, 2009), and a broad diversity of flower and plant growth habits. Zuzek et al. (1995) described diverse growth habits of roses defining descriptors, including arching, climbing, dense, groundcover, open, rugosa, spreading, and suckering. Given this diversity of forms, the role roses play in landscapes is extensive. They are found adorning roadsides, public parks, commercial spaces, and residential areas. Garden roses provide aesthetic value throughout the growing season due to both their vegetative and floral production.
Plant architecture of roses is linked to flower yield and ornamental value (Crespel et al., 2014). Previous architectural analysis of roses focused on morphological, topological, and geometrical traits, such as stem length and diameter, succession, branching, and branching angles (Godin et al.,1999). Traits identified as relevant for characterizing rose bush shape include plant height, the number and length of stems, leaf profile, the internode length, branching angles, the branching site, and branch order number (Crespel et al., 2013; Gitonga et al., 2014; Kawamura et al., 2015; Morel et al., 2009; Wu et al., 2019). Little is known about which traits are critical to the selection of specific bush shapes.
The focus of the TAMU Rose Breeding and Genetics program is the development of garden roses for the modern garden. One of the most important trends in home landscapes and gardens is low maintenance, in other words, easy-care (American Nurseryman, 2016). A rose that is low maintenance needs to be resistant to both biotic and abiotic stresses and have a full plant structure without consistent pruning. Recent surveys and studies indicate that consumer preferences for new rose traits include disease resistance, compactness, moderate height (from waist to shoulder height is preferable), a high number of evenly distributed flowers, and fragrance (Boumaza et al., 2009; Chicago Botanic Garden, 2016; Lütken et al., 2015; Waliczek et al., 2018). The objectives of the Rose Breeding and Genetics Program are to develop disease-resistant, heat-tolerant, compact plants with high flower count that are uniformly distributed on the plant and produced throughout the growing season. This research aims to identify the key growth traits responsible for the compact structure of the rose plant.
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