The plant material consisted of 47 modern cultivars of common oat, including 14 from Poland, 19 from the Czech Republic, and 14 from Germany. The cultivars were obtained from native breeders from each country, commonly used by farmers (COBORU; Saaten-Union; Selgen 2022) Polish cultivars have been recorded in the register of recommended cultivars by COBORU (Research Centre for Cultivar Testing).
A set of cultivars and lines with known resistance genes (Pm) were used as control: Jumbo (Pm1), Mostyn (Pm3), AV1860 (Pm4), Am25 (Pm5), Bruno (Pm6), APR122 (Pm7), Rollo (Pm3+Pm8), AVE2406 (Pm9), AVE2925 (Pm10), CN113536 (Pm11) and CN 67383 (Pm12). This control set has been previously used in many studies (Hsam et al., 1997, 1998, 2014, Hermann and Mohler 2018, Okoń and Ociepa 2017, Cieplak et al. 2021). The cultivar Canyon carrying the Pm7 gene also served as control. Okoń et al. (2021a) showed that resistance conditioned by Pm7 in the cultivar Canyon and line APR122 was different and these authors included the two genotypes in the control set. In addition the Pl51586 (U A.strigosa) genotype were identified as effective sources of resistance in our previous studies (Okoń and Kowalczyk 2020) and was also included in the present work. The cultivar Fuchs was used as a susceptible control (Table 1).
The level of resistance of the analysed cultivars was determined based on the infection profile of 10 single-spore Blumeria graminis f. sp. avenae isolates obtained according to a modified method described by Okoń and Kowalczyk (2012). The isolates were obtained from populations sampled in different parts of Poland in different years. All isolates are part of the collection of the Institute of Plant Genetics, Breeding, and Biotechnology. Moreover, isolates were characterised by different virulence levels to the control genotypes.
The host-pathogen tests were carried out on the first leaves of 10-day-old seedlings of oat genotypes according to a modified method described by Hsam et al. (1997). Leaf fragments were putted on round culture plates half-filled with agar (6 g of agar per 1 L of water and 35 mg × 11 of benzimidazole). Plates with leaf fragments were inoculated using an inoculation tower by placing approx. 500-700 powdery mildew spores per 1 cm2. The plates were then incubated under appropriate conditions at approx. 17°C and lighting intensity of approx. 4 kLx.
The level of infection of the tested cultivars was determined ten days after infection with the isolates using the modified Mains scale (Mains 1934); where 0 = no visible symptoms 1 = very resistant, single colonies; 2 = intermediate resistance, moderate mycelium sporulating; 3 = moderately susceptible, extensive mycelium, more sporulation; 4 = highly susceptible, large colonies and abundant sporulation. The results after infection were assigned to 3 typical plant reactions: R – resistant (0-20% infection), I – intermediate (20-50%), and S – susceptible (> 50% infection) (Tables 2,3). The result of infection scored as 0 or 1 classified the cultivar as resistant (R). A genotype infection assessed as 2 was considered an intermediate (I) response. If the infection was scored as 3 or 4, the cultivar was qualified as susceptible.