Pear scab resistance gene Rvn1 from Ussurian pear is located in a cluster of receptor-like protein ethylene-inducing Xylanase (EIX) genes.

BACKGROUND

Pear scab, caused by Venturia nashicola, is one of the most serious diseases affecting Asian pear (Pyrus spp.) production. While single-gene resistance has been used in breeding, it is often overcome by evolving pathogens. Therefore, integrating multiple resistance genes from diverse genetic backgrounds is essential for developing durable cultivars. Although resistance genes have been identified in various pear species, their nucleotide sequences remain largely unknown.

RESULTS

We fine-mapped the scab resistance gene Rvn1 from Japanese pear 'Kinchaku' to a 30,281-bp region using genotyping of 4,297 seedlings across 23 populations. Comparative sequence analysis with apple (Malus spp.) and pear pseudomolecules revealed conserved regions containing receptor-like ethylene-inducing xylanase (EIX) gene clusters, which have undergone distinct tandem and segmental duplications. Within the mapped region, only four transcripts were predicted. Their full-length sequences were obtained using Iso-Seq, enabling precise characterization of candidate resistance genes. RNA-seq analysis showed that among these genes, the gene for a receptor-like protein EIX was significantly upregulated in the resistant cultivar 'Hoshiakari' relative to the susceptible 'Kosui' and was induced upon inoculation. Population structure analysis of the region surrounding Rvn1 suggested that Rvn1 originated from Ussurian pear (P. ussuriensis), indicating potential non-host resistance against V. nashicola. Molecular markers tightly linked to Rvn1 were developed for use in marker-assisted selection.

CONCLUSIONS

We identified a receptor-like EIX gene as a strong candidate for Rvn1, a resistance gene against V. nashicola in Asian pear. Its expression pattern-being significantly upregulated in the resistant cultivar and induced upon inoculation-strongly supports its role in scab resistance. Molecular markers tightly linked to this locus were developed and are applicable to breeding programs. These findings provide a foundation for durable resistance breeding and future identification of additional resistance genes.