Races of <i>Puccinia graminis</i> f. sp. <i>avenae</i> from 2023-2024 and Resistance of Oat Cultivars in China

Oat stem rust, caused by Puccinia graminis f. sp. avenae (Pga), is a devastating fungal disease that poses a serious threat to global oat production. In recent years, with the expansion of oat cultivation area and the shortage of resistant cultivars in China, the prevalence of this disease has shown an increasing trend. There is an urgent need to clarify the population structure and virulence characteristics of P. graminis f. sp. avenae for effective disease management and resistance breeding. From 2023 to 2024, this study collected a total of 186 oat stem rust samples Hebei Province, China. Single isolates were obtained through single-uredinium, and physiological race identification and virulence frequency analysis were conducted using 12 single-gene differential lines. Additionally, two predominant P. graminis f. sp. avenae races were selected to evaluate the seedling and adult-stage resistance of 59 oat cultivars (lines). The results showed that 188 single-uredium isolates were obtained from 158 viable samples (with a survival rate of 85.0%), and seven physiological races were identified: TJD, TJN, TKN, TJB, TBD, TGD, and TJL. Among them, TJD was the predominant race (occurrence frequency 37.7% in 2023, 38.8% in 2024), TJN was the sub-predominant race (28.2% in 2023, 31.3% in 2024), and the frequencies of the remaining five races were all below 17.6%. This indicates that the P. graminis f. sp. avenae population structure in China is relatively stable with low virulence diversity. All isolates were virulent to Pg1, Pg2, Pg3, and Pg4, while avirulent to Pg6, Pg13, and Pg16. The virulence frequency to Pg10 ranged from 3.1% to 20.8%. In total, 31 (52.6%) oat cultivars were resistant to all tested races of P. graminis f. sp. avenae in field test in 2023-2024. This study supplements global P. graminis f. sp. avenae surveillance data, clarifies the race composition and virulence dynamics of P. graminis f. sp. avenae in northern China, and provides a scientific basis for the integrated management of oat stem rust and the breeding of resistant cultivars.