Molecular Mapping of Major Genes and QTLs in Pear

Pear breeding programs are mainly focused on resistance to biotic stress and fruit quality traits. In the last two decades, major efforts have been undertaken toward identification of major genes and quantitative trait loci (QTLs) linked to both biotic resistance and fruit quality traits, along with their associated molecular markers in order to enable marker-assisted selection and breeding. This chapter will cover most relevant results reported so far pertaining to markers and QTLs linked to resistance to pathogens and pests (such as fire blight, scab, brown and black spot, pear psylla, pear sludge, and blister mite), fruit quality (fruit size, firmness, skin overcolor, russeting, fruit sweetness, and fruit acidity), and other traits (such as tree habit, chilling requirement, and harvest time). Furthermore, summaries of findings of studies conducted before and after the beginning of the genomics era will be provided. In addition, all progenies and selected parental lines capable of conferring traits of interest to their progenies are described herein. The aim is to provide breeders with tools to identify pear ideotypes in which several traits can be combined into a single individual. Furthermore, knowledge of genes and their related functions should serve as the basis for pursuing new plant breeding technologies, such as cisgenesis or DNA editing. These unprecedented advances in genomics and breeding strategies promise to enable dramatic improvements in breeding efficiencies, even for pears, that will also reduce time and costs incurred in today’s traditional genetic improvement efforts.