Screening oat landraces for resistance to Blumeria graminis f. sp. avenae

Landraces have considerable potential for use in increasing genetic diversity of cultivated crops. They present a unique source of specific traits for disease and pest resistance, nutritional quality and marginal environment tolerance. In this study we screened of 156 A. sativa and A. strigosa landraces originated from Poland, for resistance to powdery mildew disease, caused by Blumeria graminis f. sp. avenae. In general, the tested genotypes showed lower level of resistance than expected. Among A. sativa landraces five were resistant to single isolates, the rest of them showed intermediate or susceptible response to B. graminis f. sp. avenae isolates used in host-pathogen tests. One A. strigosa genotype was resistant to all tested isolates and could be valuable source of resistance against oat powdery mildew.

Diseases caused by fungal pathogen are one of the main factors reducing yield and grain quality in crops production. Among them the most important are rust diseases (leaf rust, brown rust, crown rust), powdery mildew, diseases caused by members of the genus Fusarium (Bentley et al. 2006;Kuzdraliński et al. 2017Kuzdraliński et al. , 2018Figueroa et al. 2018). One of the most important foliar diseases of oat is powdery mildew caused by Blumeria graminis DC. f. sp. avenae Em. Marchal. This disease appears every year and has been reported as a serious problem in many parts of the world (Roderick et al. 2000;Sebesta et al. 1991, Banyal et al. 2016, Xue et al. 2017. Limiting the losses caused by the occurrence of this pathogen is based on appropriate agrotechniques and introduction of resistant cultivars (Gacek 2000;Tratwal and Rosiak 2010). To date, ten genes conferring resistance to oat powdery mildew have been characterised, but based on reports from available literature only a few are high effective against existing Blumeria graminis DC. f. sp. avenae populations. (Okoń 2015;Okoń and Ociepa 2017). Resistance to powdery mildew is decreasing due to the emergence of new pathogen pathotypes by mutations and recombinations. Also using the same set of resistance genes in breeding programmes could result in the selection of pathotypes with the matching virulence genes, resulting in resistance breakdown (Czembor and Czembor 2001). Menardo et al. (2016) suggested that also hybridization between formae speciales is a mechanizm of adaptation to new crops introduced by agriculture. Because of these facts there is a need to search for novel and effective sources of resistance to powdery mildew in oat. A valuable source of genetic variation, and thus the source of resistance genes can be both wild species and landraces.
Landraces are dynamic, heterogeneous crops populations composed of numerous homozygous lines or individuals with various level of heterozygosity (Boczkowska and Onyśk 2016). Landraces envolved in response to natural selection for the local environment, mutations, migrations and genetic drift. Consequently they are well adapted to local conditions including biotic and abiotic stress factors (Frankel et al. 1995;Villa et al. 2005;Mohammadi et al. 2014;Pusadee et al. 2014). Several studies suggest that landraces may be a good source of new allelic diversity for breeding programs. They are valuable sources of quality traits (Pecetti et al. 2001;Moragues et al. 2006;Li et al. 2009;Teklu andHammer 2009), agro-ecological adaptation (van Hintum andElings 1991), abiotic stresses (Reynolds et al. 2006;Trethowan and Mujeeb-Kazi 2008) and resistance to pests and diseases (Saker et al. 2008;Li et al. 2009;Sánchez-Martín et al. 2011.
Bacause of this fact, the aim of presented study was screening a group of 156 oat landraces belonging to A. sativa and A. strigosa species for resistance to Blumeria graminis f. sp. avenae causing powdery mildew in oats.
All genotypes were received from two gene banks: The Plant Breeding and Acclimatization Institute (IHAR), Radzikow, Poland and Leibniz Institute of Plant Genetics and Crop Plant Research, Gatersleben, Germany.
Host-pathogen tests described by Okoń and Kowalczyk (2012) were used to determine resistance of the analyzed genotypes. Disease on the leaves was rated 10 days after inoculation according to 0-4 modified scale (Mains 1934). Many studies aimed at identifying new sources of disease resistance are based on tests with one highly virulent pathogen isolate (Sánchez-Martín et al. 2012;Herrmann and Mohler 2018). Okoń et al. (2018) underline that it is necessary to perform tests based on a diverse set of pathogen isolates in order to obtain reliable results on the effectiveness of disease resistance. Observations based on isolates sampled in one region or in one year may be insufficient to draw reliable conclusions. In   presented study, all accessions were tested using six single spore isolates of B. graminis f.sp. avenae of divers geographic origin (Fig. 1). Their virulence was verified using a set of cultivars and lines with defined resistance genes (Table. 1).
In general, the tested genotypes showed a low level of resistance to oat powdery mildew. Among the A. sativa landraces, there were no completely resistant genotypes (0-2 in Mains scale). Among the 145 accessions, two (Ave 2663 and 51,634) were resistant to three among six tested isolates, three (Ave2813, 52,565 and 51,610) were resistant to two isolates and one genotype (51443), were resistant to single isolates. Thirty-nine of tested landraces belonging to A. sativa showed intermediate response to single isolates, but we did not identify any genotype which showed intermediate response to all tested isolates (3 in Mains scale). Most of them were susceptible to all tested B. graminis f. sp. avenae isolates (4 in Mains scale) ( Table 2).
Among tested A. strigosa genotypes one (Pl 51,586) showed resistant response to all six isolates used in hostpathogen tests. Five genotypes showed intermediate response to single isolates. The rest of them showed susceptible resopnce to B. graminis f. sp. avenae isolates used (Table 3).
Based on these tests we identify only one genotype fully resistant to B. graminis f. sp. avenae isolates. The use of different isolates allows us to conclude that the identified source of resistance is highly effective in Polish condition. Also using isolates collected in two different years may indicate that the resistance identified in the A. strigosa genotype could be also effective over a longer period of time.
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