Powdery mildew caused by Blumeria graminis is a deleterious foliar disease of cereals, including oats (Hsam et al. 1997; Dreiseitl and Wang 2007; Kaur et al. 2008; Silvar et al. 2013). Breeding of resistant cultivars is one of the most economical and environmentally friendly methods to control this pathogen. Genomic regions responsible for the resistance to powdery mildew in oat are known as Oat Mildew Resistance (OMR) groups (Jones and Jones 1979). Until now, five OMR groups have been described in oat, but there are only a few cultivars that possess powdery mildew resistant genes (Hsam et al. 1997; Kowalczyk et al. 2004; Okoń 2012). Resistance to powdery mildew is decreasing due to the emergence of new strains of this pathogen, thus there is a need to search for novel and effective sources of resistance to powdery mildew in oat (Hsam et al. 1997). The aim of the present study was to identify and characterize new sources of resistance to powdery mildew in wild and cultivated species of oat.

The material for this study consisted of 67 oat genotypes belonging to five different species: Avena sterilis, Avena fatua, Avena sativa (Table 1), Avena maroccana, and Avena murphyi (Table 2). Oat accessions were provided by genebanks: Genebank Gatersleben (Germany), Plant Gene Resources of Canada (Saskatoon, Canada), National Germplasm Resources Laboratory’s (Beltsville, USA), and IHAR (Poland).

Table 1 Differential reaction of oat hexaploid species: A. sterilis, A. fatua and A. sativa after inoculation with three differential isolates of Blumeria graminis f.sp. avenae
Full size table
Table 2 Differential reaction of oat tetraploid species: A. maroccana and A. murphyi after inoculation with three differential isolates of Blumeria graminis f.sp. avenae
Full size table

Host-pathogen tests were carried out according to the method described by Okoń and Kowalczyk (2012). The three most virulent isolates of powdery mildew were used for resistance tests. As a control, cultivars and line with documented OMR groups were used: Bruno (OMR1), Jumbo (OMR2), Mostyn (OMR3), AV1860 (OMR4), and Fuchs susceptible to powdery mildew. Control plant materials were kindly supplied by Sai L.K. Hsam from the Technical University Munich, Germany.

A total of 20 isolates of Blumeria graminis f.sp. avenae were tested for their responses to oat cultivars and lines with documented OMR groups (Table 3). Among tested isolates, three (M22, M31, M39) were chosen to screen different species of genus Avena L. and to search for new potential sources of resistance to powdery mildew. The experiment conducted in the current work showed that the resistance conditioned by OMR1, OMR2 and OMR3 genes was broken down under Polish condition. None of the 20 isolates was avirulent to these genes. Line AV1860 carrying OMR4 gene was the only one resistant to 19 out of 20 isolates. These results suggested that there is a need to identify new effective sources of resistance against powdery mildew in oat.

Table 3 Reaction of five differential oat cultivars and lines after inoculation with 20 isolates of Blumeria graminis f.sp. avenae
Full size table

Many sources of resistance to powdery mildew have been reported in common oat (Jones 1983; Hsam et al. 1997, 1998) as well as in wild relatives of A. sativa (Aung et al. 1977; Thomas et al. 1980; Herrmann and Roderick 1996; Hoppe and Kummer 1991; Hayes and Jones 1966). The study of Sebesta et al. (1991) indicated that the line Pc54, which originated from a hybrid between A.sativa cv Pendek and A.sterilis, possessed effective resistance to powdery mildew. Hoppe and Kummer (1991) reported that the line Pc39 was also to some extent resistant to powdery mildew, and could be used as a donor of resistance. Another promising source of resistance to powdery mildew is the line APR122 derived from a hybrid between A. eriantha and A. sativa. The work of Hsam et al. (1997) showed that this line was completely resistant to all isolates of Blumeria graminis studied at the seedling stage. These results suggested that hexaploid species are a valuable source of genes responsible for resistance. In the present study, three hexaploid species, A. sterilis, A. fatua and A. sativa, were tested. Two genotypes belonging to A. sterilis were resistant to all isolates used in the experiment. The remaining genotypes of A. sterilis were resistant to single isolates or showed intermediate responses (Table 1). Accessions of A. fatua tested in this study presented a susceptible or intermediate response to all isolates and had very low levels of resistance to powdery mildew (Table 1). Among A. sativa accessions, two were resistant to all tested isolates. Although all genotypes studied were resistant to the M39 isolate, after inoculation of M22 and M31 isolates, they showed a susceptible or intermediate response (Table 1). In the current work, genotypes belonging to tetraploid species presented the highest level of resistance. Among Avena species tested, very high levels of resistance were identified in A. maroccana accessions. Twelve genotypes from among 15 were resistant to all isolates of powdery mildew. The remaining A. maroccana genotypes showed an intermediate response (Table 2). Genotypes of A. murphyi also had a high level of resistance. The majority of accessions were characterized by resistant or intermediate responses of which two genotypes were resistant to all three isolates included in the experiment (Table 2). Previous studies suggest that the resistance derived from lower ploidy level could be used to improve this trait in common oat. Aung et al. (1977) successfully transferred resistance from the tetraploid species A. barbata into A. sativa. Furthermore, Yu and Herrmann (2006) were also able to effectively transfer the gene conferring resistance to powdery mildew from tetraploid species. However, transfer of a resistance gene between species at the same ploidy level is much easier. The results obtained in our study suggest that selected genotypes could be used as donors of genes encoding resistance to powdery mildew. Moreover, Hsam et al. (1997, 1998); Kowalczyk et al. (2004) and Okoń (2012) in their study identified some resistant oat cultivars possessed an unknown response pattern compared to control cultivars. These resistant genotypes could be also used as new sources of resistance in oat breeding programs.

The current study has also demonstrated that many genotypes are present in wild relatives of A. sativa that could be used as sources of new resistance to powdery mildew. Identified genotypes, especially those resistant to all isolates tested, could be used in oat breeding programs to improve the level of resistance to powdery mildew.