Genetics and Breeding of Pear

Abstract

Although Pyrus consists of 22 primary species, nearly all scion breeding is focused on three species, including Pyrus communis (European pear), Pyrus pyrifolia (sand pear), and Pyrus × bretschneideri (white pear). Most scion breeding programs around the world are in one of two camps: those breeding for European (P. communis) soft- or firm-textured pears, and those breeding for crisp-textured Asian pears (P. pyrifolia and P. × bretschneideri). Intercrossing among species is typically limited, except in New Zealand where it is a core aspect of the breeding program. The lack of effective control of pests and diseases in pear combined with increased consumer preferences for fruits grown with low chemical inputs and low environmental impacts is driving breeding programs to incorporate plant resistance to major pests and diseases. On the other hand, the range of vigor-controlling rootstocks for pear production is limited. Quince (Cydonia oblonga) rootstocks are preferred in Europe, as they offer vigor control, precocity, and ease of propagation. To date, utilization of quince rootstocks in North America has been restricted due to their lack of cold tolerance. Identification and testing of cold hardy quince selections could change this. Pyrus rootstocks are currently preferred in North America and in Asia because of their cold hardiness; however, they are more vigorous than quince, yet their yield efficiency is lower. Thus, vigor control is among breeding targets for Pyrus rootstocks. Hybrids between Pyrus species are now being used to overcome some of these deficiencies and to include adaption to highly alkaline soils. In addition, other species, such as Amelanchier, are being tested for their potentials to confer dwarfing, excellent cold tolerance, potential non-host resistance to pear decline, resistance to fire blight, and good yield efficiency. Recent identification of genetic markers for scion vigor control and precocity is a positive step for future breeding of enhanced Pyrus rootstocks. Overall, the development of cultivars and rootstocks with new or improved characters would be facilitated by the availability of molecular markers for traits of interest. However, pear breeding programs lag behind those of apple in application of marker-assisted selection and genomic selection to speed-up cultivar/rootstock development, and to ensure programs are more effective and efficient in their utilization of available resources. As current genetic markers are validated in more populations, and the pear reference genome sequence undergoes further refinement, these technologies will play a larger role in pear breeding programs.