Characterization of Rsg2.a3: A new greenbug resistance allele at the Rsg2 locus from wild barley (Hordeum vulgare ssp. spontaneum)

Greenbug (Schizaphis graminum Rondani) is a destructive insect pest that not only damages plants, but also serves as a vector for many viruses. Host plant resistance is the preferred strategy for managing greenbug. Two greenbug resistance genes, Rsg1 and Rsg2, have been reported in barley. To breed cultivars with effective resistance against various greenbug biotypes, additional resistance genes are urgently needed to sustain barley production. Wild barley accession WBDC053 (PI 681777) was previously found to be resistant to several greenbug biotypes. In this study, a recombinant inbred line (RIL) population derived from Weskan × WBDC053 was evaluated for response to two greenbug biotypes (E and TX1) and genotyped using genotyping by sequencing (GBS). A set of 3347 high quality GBS-derived single nucleotide polymorphisms (SNPs) were then used to map the greenbug resistance gene in this wild barley accession. Linkage analysis placed the greenbug resistance gene in a 2.35 Mb interval (0–2,354,645 bp) in the terminal region of the short arm of chromosome 2H. This interval harbors 15 genes with leucine-rich-repeat (LRR) protein domains. An allelism test indicated that the greenbug resistance gene in WBDC053, designated Rsg2.a3, is likely allelic or closely linked to Rsg2. GBS-SNPs 2H_1318811 and 2H_1839499 co-segregating with Rsg2.a3 in the RIL population were converted to Kompetitive allele specific PCR (KASP) markers KASP-Rsg2.a3-1 and KASP-Rsg2.a3-2, respectively. The two KASP markers can be used to select Rsg2.a3 and have the potential to tag Rsg2 in barley improvement programs.