Identification of a major QTL for Xanthomonas arboricola pv. pruni resistance in apricot

Xanthomonas arboricola pv. pruni causes bacterial spot of stone fruit resulting in severe yield losses in apricot production systems. Present on all continents, the pathogen is regulated in Europe as a quarantine organism. Host resistance is an important component of integrated pest management; however, little work has been done describing resistance against X. arboricola pv. pruni. In this study, an apricot population derived from the cross “Harostar” × “Rouge de Mauves” was used to construct two parental genetic maps and to perform a quantitative trait locus analysis of resistance to X. arboricola pv. pruni. A population of 101 F1 individuals was inoculated twice for two consecutive years in a quarantine greenhouse with a mixture of bacterial strains, and disease incidence and resistance index data were collected. A major QTL for disease incidence and resistance index accounting respectively for 53 % (LOD score of 15.43) and 46 % (LOD score of 12.26) of the phenotypic variation was identified at the same position on linkage group 5 of “Rouge de Mauves.” Microsatellite marker UDAp-452 co-segregated with the resistance, and two flanking microsatellites, namely BPPCT037 and BPPCT038A, were identified. When dividing the population according to the alleles of UDAp-452, the subgroup with unfavorable allele had a disease incidence of 32.6 % whereas the group with favorable allele had a disease incidence of 21 %, leading to a reduction of 35.6 % in disease incidence. This study is a first step towards the marker-assisted breeding of new apricot varieties with an increased tolerance to X. arboricola pv. pruni

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\u2019s traditional genetic improvement efforts