Identification and genetic mapping of novel resistance gene, Rvn4, for pear scab in Chinese pear

Abstract

Pear scab, caused by Venturia nashicola, is one of the most harmful diseases of pears, especially of Japanese and Chinese pears. The breeding of new cultivars resistant to pear scab has long been an aim of the Asian pear breeding programs. Although loci for pear scab disease resistance have been identified in Japanese and European pears, information on the genes controlling scab resistance in Chinese pears is limited. Genetic control of scab resistance in Chinese pear is reported to involve a single dominant gene. Here, we reaffirmed the scab resistance in the Chinese pear ‘Hong Li’ controls a single dominant gene and identified the exact location of a scab resistance gene, Rvn4. We first mapped Rvn4 at the top of linkage group (LG) 7 and then used public genome sequences to develop novel simple sequence repeat (SSR) markers to enrich the target region. Using these novel SSRs and the previously published SSR markers, we constructed a LG 7 of ‘Hong Li’ with an average marker density of 1.4 cM per marker. The novel SSR marker Pbr.chr07.20 had a significant linkage to Rvn4, with a genetic distance of 1.3 cM. The identification of the precise locus of Rvn4 in Chinese pear, together with previous studies in Japanese and European pear, will enhance our understanding of the mechanisms of pear scab resistance. DNA markers linked to the novel gene may also allow efficient selection of scab-resistant seedlings in pear breeding programs and the pyramiding of multiple resistance genes.