Pear (Pyrus spp.) is one of the most important fruit crops of the Rosaceae family, ranking second to apple (Malus ×domestica) in world and European production of pome fruit tree species (Food and Agriculture Organization of the United Nations, 2010). Pyrus communis is the most commonly cultivated pear species in Europe, America, and Africa, whereas Pyrus pyrifolia is the main cultivated species in Asia (Bell, 1991). Worldwide production of P. communis pears is based upon relatively few cultivars, most of them selected in late 18th and 19th century, or derived from those. Furthermore, the genetic base of cultivated pear in western Europe has significantly narrowed in the last few years. In 1986, seven cultivars accounted for ≈58% of pear production in western Europe (Bell, 1991), but nowadays, seven cultivars account for 75% of the production (World Apple and Pear Association, 2009). ‘Conference’ has become predominant in most European producing countries, and accounts for nearly one-third of European Union production. The reasons for this concentration are varied, but include economic and market factors, changes in consumption patterns, and biological aspects, such as productivity, storage ability, and susceptibility to pests and diseases (Bell, 1991).
As a consequence, many of the traditional or local cultivars have been considered obsolete and replaced, leading to a dramatic loss of genetic diversity. The recognition of the need for the collection and preservation of endangered fruit germplasm has encouraged the establishment of genetic resource conservation programs. In 1986, a germplasm bank of old and local pear cultivars was established by the Horticulture section of the ETSIA-UdL. This germplasm bank currently maintains 114 Malus and 169 Pyrus accessions, collected at 12 northern Spanish provinces (Urbina et al., 2007), at the Estación Experimental de Lleida of the Institut of Recerca i Tecnologia Agroalimentària (IRTA) in Lleida, Spain. In 2002, a research program was launched to evaluate the genetic diversity of the collection through detailed morphological and agronomical description, and fingerprinting analysis based upon molecular markers was initiated in 2005.
Microsatellite or simple sequence repeat (SSR) markers have been favored over other methods in establishing unique genetic identities or fingerprints and in assessing genetic diversity within a collection due to their high polymorphism level, reproducibility, and relative ease of analysis (Schlötterer, 2004). Moreover, SSR have also proven useful in creating core collections that represent not only the genetic structure of germplasm collections, but also their phenotypic structure (Santesteban et al., 2009). The SSR markers used in the earliest studies in pear were derived from apple (Yamamoto et al., 2001; Hemmat et al., 2003), as apple proved to be highly conserved in pear. However, after the development of SSR derived from asian pear (P. pyrifolia) and european pear (P. communis) (Fernández-Fernández et al., 2006; Yamamoto et al., 2002a, 2002b), SSR derived from Malus and Pyrus have been used to reveal pear genetic diversity among pear cultivars (Bao et al., 2007; Bassil et al., 2008, 2009; Brini et al., 2008; Ghosh et al., 2006; Jiang et al., 2009; Katayama et al., 2007; Kimura et al., 2002; Sisko et al., 2009; Volk et al., 2006; Wünsch and Hormaza, 2007; Xuan, 2008).
The present study aims to determine the genetic identity of the Pyrus accessions curated at the ETSIA-UdL Germplasm Bank, to estimate the genetic diversity of the collection, to identify the genetic structure and relationships among its accessions, and to establish a representative core collection, using a set of highly informative SSR markers, to optimize the conservation and use of this germplasm.
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