# Predictions of Genes Conferring Resistance to Puccinia hordei in an International Barley Panel Using Gene-for-Gene-Based Postulations and Linked Molecular Markers

## TL;DR

This study identifies genes in barley that help resist a leaf rust disease, using molecular markers and pathotype testing to guide breeding efforts.

## Contribution

The study identifies novel resistance sources and provides insights into virulence profiles of Australian Puccinia hordei pathotypes.

## Key findings

- Four known all-stage resistance genes (Rph2, Rph3, Rph9.am, Rph25) were identified in 77 barley genotypes.
- Three barley entries (CG55, CG56, CG57) showed potential novel resistance not linked to known Rph genes.
- Adult plant resistance (APR) was prevalent in 83% of entries, with Rph24 being the most common APR gene.

## Abstract

Deployment of resistant barley cultivars is the most cost-effective and environmentally responsible strategy to manage barley leaf rust caused by Puccinia hordei. Gene predictions based on screening of germplasm with an array of well-characterised pathotypes and application of molecular markers serve as a pivotal step for identification, characterisation, and deploying resistance in breeding programmes. We evaluated 77 barley genotypes from 17 countries using an array of diverse P. hordei pathotypes and molecular markers to predict resistance gene identities. Evaluation and resistance analysis of the panel determined four known all-stage resistance (ASR) genes—Rph2, Rph3, Rph9.am, and Rph25 present individually or in combination, with Rph3 being the most common (33% of entries) and Rph2 the second most frequent (9%). Three entries, CG55, CG56, and CG57, exhibited low infection to all tested pathotypes and were negative for markers associated with Rph7, Rph15, and Rph28, potentially carrying novel uncharacterised resistance. In addition to ASR, our studies demonstrated that the core panel had a high prevalence of adult plant resistance (APR) to P. hordei, occurring in ~83% of entries. By employing markers linked to APR, we were able to partition known APR with Rph24 found in the most lines (60%), followed by Rph23 (17%), Rph20 (14%), and uncharacterised (9%) either individually or in combination. The resistance sources identified in this study can be effectively utilised and combined by breeding programmes to diversify their resistance gene pool. Our study also revealed the virulence and avirulence profiles of 12 Australian P. hordei pts to catalogued Rph genes, providing pathologists and breeders with insights into combining genes relevant to their breeding regions and pathogen shifts.