Resistance to Puccinia graminis f. sp. avenae in Oat Genotypes and Challenges for Genetic Breeding in Argentina
Abstract
Oat stem rust caused by Puccinia graminis f. sp. avenae (Pg) significantly threatens oat cultivation globally and in some areas of Argentina, emphasizing the importance of studying local germplasm resistance. We evaluated 38 Argentine oat cultivars (16 old, 22 modern) and 20 breeding lines against prevalent Pg races (2005, 2021, 2022, and 2023) in both seedlings (greenhouse) and adult plants (field trials). We postulate several candidate genes (Pg3, Pg9, Pg10, Pg15, and Pga) in the tested germplasm. Seedling assays revealed a shift in cultivar resistance, with older cultivars becoming increasingly susceptible to recent Pg populations. Modern cultivars and lines exhibited limited seedling resistance, highlighting the vulnerability of current germplasm. Adult plant results showed variations in disease severity in some genotypes among years, suggesting shifts in Pg race prevalence and virulence. Resistance observed in cultivars such as Milagros, Payé, Aikén, and Yapa to specific races at the seedling stage may explain their favorable performance in certain seasons. Moreover, cultivars such as Máxima, Tucana, Polaris, U16, Maná, La Plata FA, and some lines showed severity values below 20% in the field. The findings provide useful insights into oat breeding programs and crop management strategies. Highlights: Resistance to oat stem rust was evaluated in 58 Argentine oat genotypes using historical and recent populations of Puccinia graminis sp. avenae. Resistance genes Pg10, Pga, Pg9, Pg3, and Pg15were postulated in cultivars and advanced breeding lines. Old cultivars showed substantial losses in seedling resistance against recent pathogen races. Modern cultivars and breeding lines exhibited limited seedling resistance, revealing the vulnerability of modern oat germplasm. Máxima INTA, INIA Tucana, INIA Polaris, U16, B.I. Maná, and several breeding lines showed consistently low stem rust severity under field conditions.