Resistance to leaf rust in rye accessions deposited at the USDA National Small Grains Collection

Rye leaf rust, caused by the fungus Puccinia recondita f. sp. secalis (Prs), is one of the most important diseases of rye. However, limited research has been conducted in the United States on this disease. Our study aimed to identify new sources of leaf rust resistance that can be incorporated into rye breeding programs. We evaluated 500 rye accessions from the USDA-ARS National Small Grains Collection (Aberdeen, ID) and four cultivars for leaf rust resistance at the seeding stage against seven Prs cultures and five derived isolates collected in 2024 across the United States. Pairwise comparisons among the seven Prs cultures, based on phenotypic responses across rye accessions, revealed virulence variation in the pathogen. Although at low frequency, resistance was observed against all the Prs cultures evaluated, ranging between 1.6 and 2.8%. Likewise, a high proportion of accessions exhibiting a heterogeneous response (having resistant and susceptible plants) was observed in this collection, ranging from 12.3% to 20.5%. Resistant accessions originated mostly from Turkey, Portugal, Germany, USA, Poland, Russia, Hungary, and Argentina. Two Argentinian cultivars (PI 534988 and PI 535015) and one perennial rye, Secale strictum (PI 630969), were resistant to all Prs cultures. Additionally, 11 accessions of cultivated rye exhibited either resistant or heterogeneous infection types across all the Prs cultures, offering valuable genetic resources for annual and perennial cultivated rye breeding.