Genetic mapping of two quantitative resistance loci to Venturia nashicola in an interspecific pear family

Abstract

Pear scab is a major disease of pear worldwide and is caused by two distinct species that are aligned with different commercial Pyrus species: Venturia pirina with European pear (P. communis) and V. nashicola with Asian pear species P. pyrifolia, P. ussuriensis and P. X bretschneideri. As these host-pathogen systems are mutually exclusive, interspecific pear breeding provides an avenue for breeding new scab-resistant cultivars. Here we describe the genetic mapping of resistance to V. nashicola in a pear progeny between interspecific pear selection P019R045T042 and ‘Shinko’ (P. pyrifolia) consisting of 274 seedlings, which was phenotyped twice with V. nashicola inoculum prepared from scab-infected leaves collected from trees of susceptible ‘Niitaka’ (P. pyrifolia). A set of 613 polymorphic DNA markers were selected from the apple and pear Illumina Infinium^® II 9K single nucleotide polymorphism array and genotyping-by-sequencing for the creation of the parental genetic maps with JoinMap v4.1. Using the Interval Mapping module in MapQTL v6.0 software, two significant quantitative trait loci were detected in P019R045T042: one on linkage group (LG) 7 and another on LG10, which we name Rvn5 and Rvn6, respectively. Both Rvn5 and Rvn6 displayed weak additive effects for pear scab (V. nashicola) resistance when both loci worked together in this family. They will contribute to more strong resistance based on gene pyramiding through marker-assisted selections for the introduction of non-host resistance into both Asian and European pears through interspecific hybridization.