Submitted to: Wild Crop Relatives: Genomic and Breeding Resources
Publication Type: Book / Chapter
Publication Acceptance Date: August 9, 2010
Publication Date: March 1, 2011
Citation: Bell, R.L., Itai, A. 2011. Pyrus. In: Kole, C., editor. Wild Crop Relatives: Genomic and Breeding Resources. Berlin, Germany: Springer-Verlag. p. 147-177.
Pear species belong to the genus Pyrus, the subtribe Pyrinae, the subfamily Maloideae (Pomoideae) in the family Rosaceae. There are at least 26 widely recognized primary species and 10 naturally occurring interspecific hybrid taxa, which are distributed in Europe, temperate Asia and mountainous areas of northern Africa. All species of Pyrus are intercrossable, and there are no major incompatibility barriers to interspecific hybridization. Information on genetic erosion for this genus is limited with only nine taxa listed on the IUCN Red List. Conservation efforts consist mainly of ex situ collections of cultivated germplasm. Chloroplast DNA, nuclear ribosomal DNA internal transcribed spacer regions, and other molecular markers have been useful in describing relationships, especially among Asian species. Classical and molecular genetic studies have dealt with the major cultivated species, Pyrus communis, P. pyrifolia, and P. ×bretschneideri. Although, most studies have used populations within a single species, some interspecific hybrid populations have been useful for the study of fruit texture, resistance to fire blight, Fabraea leaf spot and pear psylla, and a few other traits. Some Asian species, notably P. ussuriensis, are a source of resistance to fire blight and pear psylla, P. communis is resistant to Asian pear scab, and interspecific breeding has been performed for these traits. Other species may be sources of valuable rootstock traits, specifically adaptation to various biotic and abiotic stresses. For example, breeding has commenced to incorporate tolerance to high pH soils in dwarfing rootstocks for European pear. Molecular marker technologies have been used mainly to study genetic diversity and relationships, and to construct a few genetic linkage maps, including two which involve interspecific hybridization between P. communis and P. pyrifolia. Other genomic resources, such as EST libraries, are less well developed than in other species of the Rosaceae such as apple, peach, and strawberry, but efforts to expand those resources are underway, especially in P. pyrifolia. These genomic resources have been developed within the three major cultivated species, and minor species have, thus far, played no role.