A Novel Pear Scab (Venturia nashicola) Resistance Gene, Rvn3, from Interspecific Hybrid Pear (Pyrus pyrifolia × P. communis)

Abstract

Asian pear scab is a fungal disease caused by Venturia nashicola. The identification of genes conferring scab resistance could facilitate the breeding of disease-resistant cultivars. Therefore, the present study aimed to identify a scab-resistance gene using an interspecific hybrid population ((Pyrus pyrifolia × P. communis) × P. pyrifolia). Artificial inoculation of V. nashicola was carried out for two years. The segregation ratio (1:1) of resistant to susceptible individuals indicated that resistance to V. nashicola was inherited from P. communis and controlled by a single dominant gene. Based on two years phenotypic data with the Kruskal-Wallis test and interval mapping, 12 common markers were significantly associated with scab resistance. A novel scab resistance gene, Rvn3, was mapped in linkage group 6 of the interspecific hybrid pear, and co-linearity between Rvn3 and one of the apple scab resistance genes, Rvi14, was confirmed. Notably, an insertion in pseudo-chromosome 6 of the interspecific hybrid cultivar showed homology with apple scab resistance genes. Hence, the newly discovered Rvn3 was considered an ortholog of the apple scab resistance gene. Since the mapping population used in the present study is a pseudo-BC₁ population, pyramiding of multiple resistance genes to pseudo-BC₁ could facilitate the breeding of pear cultivars with durable resistance.

Keywords: InDel; disease resistance; genetic linkage map; ortholog; single dominant gene.

Figure 1

Linkage group (LG) 6 of ‘Greensis’ (G6) with the novel pear scab resistance gene, Rvn3, highlighted in blue. The number on the left of each marker indicates genetic distance (cM). The red marker is the SSR developed in bacterial artificial chromosome clone of HcrVf2 regarded as candidate for apple scab resistance gene (Vf) [17]. The two graphs on the right represent the logarithm of odd (LOD) for each locus in 2016 and 2018.

Figure 2

Alignment results of paired reads in ‘Greensis’ (a,b) and ‘Whasan’ (c,d). Gray reads are a match for the reference genome. Red reads indicate insertions that are larger than expected. Empty reads (colored white) indicate that none of reads are aligned to the reference genome. The ‘I’ colored purple is a small InDel variation.