Identification of a new Rsg1 allele conferring resistance to multiple greenbug biotypes from barley accessions PI 499276 and PI 566459

Greenbug [Schizaphis graminum (Rondani)] is a major insect pest that significantly affects barley production worldwide. The identification of novel greenbug resistance genes is crucial for sustainable barley production and global food security. To identify greenbug resistance genes from a US breeding line PI 499276 and a Chinese cultivar PI 566459, two F_6:7 recombinant inbred line (RIL) populations developed from crosses Weskan × PI 499276 and Weskan × PI 566459 were phenotyped for responses to greenbug biotype E and genotyped using genotyping-by-sequencing (GBS). Linkage analysis using single nucleotide polymorphism and kompetitive allele-specific polymorphism (KASP) markers delimited the greenbug resistance genes from PI 499276 and PI 566459 to a 1.2 Mb genomic region between 666.5 and 667.7 Mb on the long arm of chromosome 3H in the Morex Hordeum vulgare r1 reference sequence. Allelism tests based on responses of four F₂ populations to greenbug biotype E indicated that the greenbug resistance gene in PI 499276 and PI 566459 is either allelic or very close to Rsg1. Given that PI 499276 and PI 566459 shared the same unique resistance pattern to a set of 14 greenbug biotypes, which is different from those of other Rsg1 alleles, they carry a new Rsg1 allele. The greenbug resistance genes in Post 90, PI 499276/PI 566459, and WBDC 336 were designated as Rsg1.a1, Rsg1.a2, and Rsg1.a3, respectively. KASP markers KASP-Rsg1a3-1, KASP-Rsg1a3-2, and KASP160 can be used to tag Rsg1.a2 in barley breeding.