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Article

Searching for Novel Oat Crown Rust Resistance in Diploid Oat Avena strigosa Schreb. Reveals the Complexity and Heterogeneity of the Analyzed Genebank Accessions

by
Sylwia Sowa
1,
Volker Mohler
2 and
Edyta Paczos-Grzęda
1,*
1
Institute of Plant Genetics, Breeding and Biotechnology, University of Life Sciences in Lublin, 20-950 Lublin, Poland
2
Institute for Crop Science and Plant Breeding, Bavarian State Research Center for Agriculture (LfL), 85354 Freising, Germany
*
Author to whom correspondence should be addressed.
Agriculture 2023, 13(2), 296; https://doi.org/10.3390/agriculture13020296
Submission received: 17 November 2022 / Revised: 18 January 2023 / Accepted: 23 January 2023 / Published: 26 January 2023
(This article belongs to the Special Issue Germplasm Resources Exploration and Genetic Breeding of Crops)
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Abstract

:
Crown rust, one of the most destructive diseases of oat, regularly occurs worldwide and leads to significant yield losses. The constant evolution of the Puccinia coronata f. sp. avenae pathogen causes a rapid decline in the effectiveness of currently used crown rust resistance genes, so new ones are urgently needed. In this study, 39 accessions of Avena strigosa Schreb. from ten countries gathered from the Polish National Genebank were evaluated at the seedling stage for crown rust reaction using a detached leaf assay and five isolates of P. coronata with diverse virulence profiles. Ten plants of each accession were tested, and 28 diverse infection profiles (IPs) were defined. One hundred and sixty-eight out of 390 plants revealed an IP of unidentified resistance. Thirty-eight (97%) of the accessions studied showed a heterogeneous infection pattern, none of the accessions displayed homogeneous susceptibility, and one (51887) was homogeneously resistant to all races used. The obtained results confirmed the complexity and heterogeneity of the accessions gathered in the genebanks. A. strigosa preserved as complex populations could be a valuable source of resistance to crown rust and potentially other pathogens. The variability of the analyzed populations was ascertained by a detailed diversity analysis of the transformed resistance/susceptibility data. The averaged resistance rating for the genebank specimens available in the databases may be an obstacle in revealing the beneficial alleles of genes hidden among the plants representing accessions preserved as complex populations. Potential donors of effective resistance may be discovered even in accessions with general susceptibility, which is a promising alternative at a time when making new collections of wild and weedy accessions is under threat from agricultural practice and climate change.

1. Introduction

Oat is a cereal cultivated worldwide with a high range of applications from animal feed to pharmaceuticals and the food industry [1]. The global production of oat is severely affected by rust diseases [2]. Crown rust caused by Puccinia coronata f. sp. avenae regularly occurs worldwide and poses a great threat to oat yield and quality. The use of fungicides is common to prevent crown rust development; however, it is becoming more and more unaffordable for consumers. Moreover, the number of registered fungicide active ingredients for the control of P. coronata is often limited. Therefore, genetic resistance is one of the most important modern oat breeding goals. The complex life cycle of P. coronata leads to the emergence of new rust races and causes high virulence dynamics and phenotypic diversity [3,4]. The efficient adaptability of the fungus is resulting in a rapid breakdown of crown rust resistance genes in existing oat varieties, hence the need for new sources of P. coronata resistance genes for the introgression and genetic enhancement of existing oat varieties.
While most Pc genes have been identified in the wild hexaploid oat A. sterilis [5], some have come from lower ploidy species, although their introduction into hexaploid A. sativa is much more difficult and demanding due to the lack of chromosome homology and the special technical requirements [6,7]. Pc91 is the only crown rust resistance gene successfully introduced into cultivated oat from a wild tetraploid. This gene was transferred from the accession A. magna CI 8330 [8] and remains effective in Europe, although virulence to Pc91 has already been recorded in Canada [9,10,11], Australia [12], and the USA [13]. Slightly better results were obtained in the case of the diploid black oat A. strigosa Schreb. often called black, sand, or bristle oat. Pc23 and Pc94 have been incorporated into a stable A. sativa background and used in oat resistance breeding [6,14]. Pc94 originating from A. strigosa accession RL1697 is still in use in the modern varieties ‘Leggett’ and ‘Stride’ [15,16]. Recently in the studies of Rines et al. [17], a new and highly effective source of adult plant resistance to oat crown rust was identified in the diploid oat A. strigosa accession PI 258731 and introgressed into the hexaploid cultivated oat.
According to Vavilov [18], the origin of A. strigosa is northwestern and western Europe with the diversity center in northern Portugal and northwestern Spain, where a whole complex of endemic forms of this species was found [19]. A. strigosa was widely cultivated for grain fodder in many European countries and is currently grown to a limited extent on the marginal soils of Scotland and Lithuania [20,21,22]. The grain of this species is distinguished from common oat by its high nutritional value, manifested in a higher content of polysaccharides (38–72% more), fat (14–27% more), and protein (27–52% more) as well as health-promoting ingredients such as phenolic alkaloids, phenolic acids, tocopherols, tocotrienols, and β-glucan [23]. A. strigosa has also been reported as a carrier of genes for resistance to Ustilago avenae (Pers.) Rostr. (smut), Puccinia graminis Pers. f. sp. avenae Eriks. & E. Henn. (stem rust), and Heterodera avenae Woll. (cereal cyst nematode) [24,25,26].
Many researchers have proven that A. strigosa is a rich source of useful genes and has a high potential for oat variety improvement. Despite the crossing barriers, the ever-evolving genome editing technology offers an opportunity for the easier insertion of the desired genes utilizing targeted genome engineering techniques [27]; so, it is worth characterizing possible donors of valuable breeding traits. Previous research focused on the screening of A. strigosa accessions gave the first insight into the resistance potential of this species [28,29,30]. The current work complements the existing data and reveals the spectrum of putative new resistance genes or alleles present in the diploid sand oat gathered by the Polish Genebank (National Centre For Plant Genetic Resources, The Plant Breeding and Acclimatization Institute, NRI, Radzików, Poland). Considering the presumable heterogeneity of the analyzed populations, testing many plants of one accession was conducted with the use of various P. coronata races. Such an approach enabled us to reveal the complexity of the studied wild species populations gathered in the genebanks and to identify the most resistant individuals.

2. Materials and Methods

2.1. Plant Material and Virulence Assessment

The study was carried out on 39 accessions of A. strigosa (Table 1) obtained from the National Centre for Plant Genetic Resources in Radzików, Poland. The accessions were landraces from Poland (22 accessions), the United Kingdom (5 accessions), Spain (2 accessions), Chile (2 accessions), Russia (2 accessions), France (1 accession), Uruguay (1 accession), the Netherlands (1 accession), Bulgaria (1 accession), and Brazil (1 accession). The origin of one accession was unknown.
The reactions of the seedlings to crown rust were recorded using five P. coronata race isolates with the virulence profile characterized based on the susceptibility/resistance reaction of 34 differential oat lines with single Pc genes [31,32], described by Paczos-Grzęda et al. [31,33]. CR230, CR241, and CR257 were obtained from the Morden Research and Development Centre, AAFC, Canada, whereas 94(63) and 51(22) were selected from a collection of races’ isolates originating from populations collected in Poland [34].
Ten seedlings from each A. strigosa accession were tested with all five P. coronata races using a detached leaf assay [35], according to the host–pathogen test methodology of Hsam et al. [36] with modifications [34]. The leaves were placed into Petri dishes or 12-well culture plates filled with agar medium (0.6%) with benzimidazole (3.4 mM) using susceptible cv. Kasztan as the infection control in each well [37]. The inoculations were performed in a settling tower, and the plates were incubated for 10 days and assessed using an infection type (IT) qualitative scale [38,39]. The infection results were transformed to HS, S, MS, MR, and R as described by Sowa and Paczos-Grzęda [34,37,40].

2.2. Data Mining and Analysis

The reactions to the isolate infections were grouped into two classes: the phenotypes described as HS, S, and MS were considered susceptible, and the remainder were considered resistant. The infection profiles (IP) of differential lines were compared with the infection profiles assigned to the analyzed A. strigosa seedlings to select the genotypes with crown rust resistance conditioned by genes not described so far. The infection scores were transformed into a binary matrix. Each plant’s resistance response level to a particular P. coronata race was treated as a single variable. The resistance or susceptibility was considered as 1 or 0, respectively. The phenotypic diversity of the accessions was described by the Normalized Shannon diversity index (Sh) [41] and Nei’s diversity (Hs) [42,43], calculated by the Virulence Analysis Tool (VAT) software [44,45]. For hierarchical clustering, dissimilarity matrices were used to construct a dendrogram using Ward’s method. Principal component analysis (PCA) was performed to visualize the relationships between the accessions. The groups and subgroups were determined with 1000 bootstrap analyses performed in PAST 4.11 software [46]. The analysis of molecular variance (AMOVA), performed by GenAlex 6.502 [47], was used to partition the diversity [48]. The variance components were tested statistically using 9999 permutations. The binary data were also evaluated for population structure using a model-based Bayesian clustering in STRUCTURE v2.3.4 [49]. The models were computed for K = 1 ÷ 10 (K—number of subpopulations). Each model was tested ten times with 10,000 burn-in cycles and 100,000 iterations. The results were tested to find the best model with the highest ΔK value using the web-based software StructureSelector [50] integrating the Clumpak program [51].
Table
Table 1. Crown rust resistance phenotypes of Avena strigosa L. genotypes. Accessions, within which fully resistant plants were present, are highlighted in grey.
Table 1. Crown rust resistance phenotypes of Avena strigosa L. genotypes. Accessions, within which fully resistant plants were present, are highlighted in grey.
No.Plant IDOriginPuccinia coronata Race 1Infection Profile
(Number of Resistant Seedlings) 2		Diversity 3
51(22)94(63)CR230CR241CR257ShHs
151022BrazilHS, SMS, RS, MS, RS, RHS, R0 (2), 1.2 (6), 2.5 (1), 4.1 (1)0.4730.200
251199BulgariaHS, SHS, S, MSS, MS, RS, HSHS, S, MS0 (9), 1.3 (1)0.1410.036
351326unknownSS, MSMS, MR, RHSHS0 (7), 1.3 (3)0.2650.084
451518PolandHS, S, MS, RHS, MSHSHS, S, MSHS0 (7), 1.1 (3)0.2650.084
551520PolandHS, S, RHS, MS, RHSHS, S, MS, MRHS0 (4), 1.1 (2), 1.2 (2), 1.4 (1), 2.1 (1)0.6390.204
651523PolandHS, S, MS, RHS, MS, RHSHS, MS, RHS, S, MR, R1 (3), 1.2 (1), 1.5 (2), 2.4 (2), 2.8 (1), 3.7 (1)0.7360.280
751524PolandHS, S, MS, RHS, MS, RHSHS, MS, MR, RHS, S, MS0 (3), 1.1 (3), 1.2 (1), 1.4 (1), 2.3 (1), 2.4 (1)0.7140.236
851575HollandSMR, RMRHS, MS, RHS, R2.5 (2), 3.2 (5), 4.1 (3)0.4470.148
951578UruguayHRHRRRHS, S, MS, MR4.4 (9), 5 (1)0.1410.036
1051579RussiaHS, S, RHS, S, MSHSHS, S, MS, RHS0 (4), 1.1 (5), 1.4 (1)0.4100.136
1151581RussiaHS, S, MS, RHS, S, MS, RHSHS, S, MSHS0 (9), 2.1 (1)0.1410.072
1251582SpainHSRMS, MRSMS2 (1), 2.5 (9)0.1410.036
1351583SpainRMR, RHS, RRHS, R3.8 (1), 4.2 (1), 5 (8)0.2780.100
1451584FranceHS, RHSHSS, MS, RHS, S0 (8), 1.1 (1), 2.3 (1)0.2780.100
1551585PolandHS, S, MS, RHS, SMR, RS, MS, RMS, R3 (1), 2.7 (6), 3.1 (2), 3.6 (1)0.4730.136
1651586PolandHS, S, MS, MR, RHS, S, MR, RHS, S, MR, RHS, S, MS, RHS, R0 (3), 1.1 (2), 1.2 (2), 2.1 (1), 2.3 (1), 5 (1)0.7360.332
1751596ChileHRRRRHS, HR4.4 (9), 5 (1)0.1410.036
1851597ChileHS, S, MS, MR, RRRRS3.5 (3), 4.4 (7)0.2650.084
1951598PolandS, MSMS, MR, RHS, SSHS, S, MS, R0 (1), 1.2 (8), 1.5 (1)0.2780.100
2051613PolandHS, RS, MS, RHSHS, SHS, S0 (9), 2.1 (1)0.1410.072
2151630PolandS, MRMS, MRHSHSHS0 (8), 1.2 (1), 2.1 (1)0.2780.100
2251732PolandS, MS, MRMR, RMR, RMS, MR, RS, MS, MR, R2.5 (5), 3.2 (1), 3.5 (2), 4.1 (1), 4.4 (1)0.5900.196
2351750PolandS, MS, MR, RMR, RMS, MR, RS, MS, RHS, MS, MR, R2.9 (1), 2.8 (2), 3.2 (1), 4.1 (2), 4.4 (3), 5 (1)0.7360.360
2451751PolandHS, S, MS, RHSHSHS, MSHS, R0 (5), 1.1 (4), 1.5 (1)0.4100.132
2551753PolandS, MS, MRMR, RMS, RMSMS, MR, R2 (1), 2.5 (1), 2.9 (5), 3.2 (1), 4.3 (2)0.5900.224
2651754PolandS, MS, MRS, MS, MRMR, RSHS3 (7), 2.5 (2), 3.4 (1)0.3480.120
2751755PolandMS, RMS, MR, RMS, RS, MSHS0 (1), 1.2 (7), 2.1 (1), 3.4 (1)0.4080.136
2851887PolandMR, RMR, RRMR, RMR, R5 (10)0.0000.000
2951987PolandS, RMS, MR, RS, MS, RS, MS, RHS, S, MS, R0 (1), 1.2 (1), 2.9 (2), 4.4 (2), 5 (4)0.6390.420
3052339PolandS, MSS, MS, MR, RS, MSS, MS, MR, RHS0 (3), 1.2 (2), 1.4 (3), 2.6 (2)0.5930.196
3152340PolandSMR, RS, MSS, RHS, S, MS, R2 (6), 2.6 (2), 2.9 (1), 3.3 (1)0.4730.148
3252341PolandMR, RS, MSMS, MR, RMSS, MS, MR, R7 (2), 2.4 (3), 3.1 (5)0.4470.148
3352342PolandMS, MR, HRMS, MR, HRMR, HRMS, MR, RMS, R3.1 (1), 3.5 (1), 4.3 (2), 5 (6)0.4730.192
34501048PolandHS, S, MR, RHSHS, MSHSHS0 (8), 1.1 (2)0.2170.064
35502855United KingdomMS, MR, HRSS, MS, MR, RSHS1 (4), 1.3 (1), 2.2 (5)0.4100.132
36502856United KingdomMR, RMS, RMS, MR, RMS, MRHS, MS, MR, R1 (5), 2.3 (1), 2.4 (1), 2.8 (1), 3.1 (1), 5 (1)0.6510.288
37502857United KingdomMS, MRHS, RMSS, MSHS, R0 (8), 1.5 (1), 2.8 (1)0.2780.136
38502858United KingdomS, MS, MRHSSMSHS0 (9), 1.1 (1)0.1410.036
39502859United KingdomS, MSHSS, MS, MRSHS0 (9), 1.3 (1)0.1410.036
1 Resistance phenotype: HS = 4 = highly susceptible—large pustules with little or no chlorosis; S = 3 = susceptible—moderately large pustules with little or no chlorosis; MS = 2 = moderately susceptible—moderately large pustules surrounded by extensive chlorosis; MR = 2N, 2C, ;1C = moderately resistant—small pustule surrounded by chlorosis or necrosis; R = ;-N, ;C, ;+C, ;1N = resistant—chlorotic or necrotic flecking; and 0 = HR = highly resistant—no visible reaction. 2 IP—infection profile—infection pattern determined for the five tested isolates characterized in Table 2; the number of resistant seedlings in brackets. 3 Sh—Normalized Shannon diversity index; Hs—Nei’s diversity.
Table
Table 2. The infection profiles (IP) of the tested A. strigosa accessions based on the reaction to P. coronata race infection.
Table 2. The infection profiles (IP) of the tested A. strigosa accessions based on the reaction to P. coronata race infection.
Puccinia coronata RaceOat Differential Line with
a Corresponding Phenotype
IP51(22)94(63)CR230CR241CR257
0H 1HHHH-
1.1LHHHHPc36, Pc39, Pc55, Pc61, Pc70, Pc71
1.2HLHHH-
1.3HHLHH-
1.4HHHLH-
1.5HHHHL-
2.1LLHHHPc38, Pc63
2.2LHLHH-
2.3LHHLH-
2.4LHHHL-
2.5HLLHH-
2.6HLHLH-
2.7HHLHL-
2.8LLHHL-
2.9HLHHLPc14
3.1LHLHLPc48, Pc103-1
3.2HLLHL-
3.3HLHLLPc35
3.4LLLHH-
3.5HLLLH-
3.6HHLLLPc54, Pc62, Pc64, Pc96, Pc97, Pc98
3.7LHHLL-
3.8LLHLH-
4.1HLLLLPc45, Pc51, Pc101, Pc104
4.2LLHLLPc59, Pc60, Pc91
4.3LLLHLPc52
4.4LLLLHPc56, Pc68
5LLLLL-
1 H = high infection (virulent reaction); L = low infection (avirulent reaction).

3. Results

Five P. coronata isolates were used to perform the host–pathogen tests on ten plants of each of the 39 A. strigosa accessions. The host reactions ranged from highly susceptible (HS) to highly resistant (HR) (Table 1). All of the tested A. strigosa accessions displayed heterogeneous phenotypes. None of the accessions was completely susceptible to all P. coronata races; however, 118 of all 390 tested plants were susceptible to all P. coronata pathotypes. The largest number of resistant plants (177) was found for the most aggressive race 94(63), which was virulent to 18 of 34 evaluated Pc genes. Resistance to the 51(22) race was shown by 146 plants, and 148 plants were resistant to CR230. The lowest number of resistant plants, 96 and 97 were obtained for race CR241 (virulent to 13 Pc genes) and CR257 (virulent to 11 Pc genes), respectively. For nine accessions (51199, 502858, 502859, 501048, 51326, 51518, 51751, 51579, and 51598), only single seedlings were rated as resistant or moderately resistant to one crown rust race. Thirty-three plants within nine accessions (Table 1) were fully resistant to all the crown rust races used. Within accessions 51578 from Uruguay and 51596 from Chile, one plant each was resistant to all races, and nine plants were immune only to CR257. The exceptional accession was 51887 originating from Poland, which was resistant or moderately resistant to all P. coronata races.
Based on the seedling reactions to the five P. coronata races, 28 infection profiles (IPs) were determined for the 390 A. strigosa plants (Table 2). IP 0 corresponded to virulent reactions to all of the rust races. Resistance to one of five races was assigned as IP 1.1–IP 1.5, while resistance to two races was described as IP 2.1–IP 2.8. IP 3.1–3.8 indicated a combination of resistance to three crown rust races. Resistance to four races was assigned as IP 4.1–4.3, and resistance to all five races was assigned as IP 5.
The IPs of the A. strigosa accessions were compared with the IPs of the differential Pc lines. The infection profile of the reference lines containing genes Pc36, Pc39, Pc55, Pc61, Pc70, and Pc71 corresponded to IP 1.1 (Table 2) and was present within nine accessions (Table 1). The Pc38 and Pc63 lines were identical with IP 2.1, as observed within six accessions. The resistance to 94(63) and CR257 was characteristic of the differential line for Pc14. This pattern was assigned as IP 2.9 and was observed for four accessions. IP 3.1 corresponded to Pc48 and Pc103-1 and was found in two accessions. IP 3.3 (Pc35), IP 3.6 (Pc54, Pc62, Pc64, Pc96, Pc97, and Pc98) and IP 4.2 (Pc59, Pc60, and Pc91) were observed in one accession each. IP 4.1 with a virulent reaction to 51(22) was identical with Pc45, Pc51, Pc101, and Pc104 and was present within four accessions. IP 4.3 corresponding to Pc52 was present within two accessions. IP 4.4 (Pc56, Pc68) was observed within six accessions.
The variation within the accessions was assessed based on the level of the resistance reaction of each plant inoculated with five isolates of P. coronata. The average values of both calculated coefficients were 0.383 for the Normalized Shannon index (Sh) and 0.143 for Nei’s diversity index (Hs). In the group with the lowest variation, we found accessions wherein all individuals were characterized by a low level of resistance to the tested isolates (51199, 51581, 51582, 51613, 502858, and 502859), as well as accessions wherein all individuals were highly resistant to all (51887) or almost all (51578 and 51596) isolates (Table 1). The greatest diversity was observed in accessions 51586, 51750, 51523, and 51987. These were mixtures of individuals with different levels of resistance to all P. coronata isolates, displaying the highest level of heterogeneity.
The analysis of molecular variance (AMOVA) determined that the majority of the observed variability was due to variation among accessions (64%, p = 0.001). The variation within the accessions accounted for 36% of the total variation.
The first two axes of the principal component analysis (PCA) of the accessions explained 51.3% of the total variance (41% and 11.3%, respectively) (Figure 1). The plot presented a large variation; however, a clear identification of groups composed of resistant or moderately resistant accessions was possible. The most resistant accession 51887 was localized on the opposite side of the plot along with 51583 and 52342. The middle part of the plot was occupied by genotypes with large variations in the immune response, e.g., 52341 (Sh = 0.447; Hs = 0.148), 502856 (Sh = 0.651; Hs = 0.288), and 52340 (Sh = 0.473; Hs = 0.148).
A dendrogram based on the accessions’ dissimilarity identified two main clusters, composed of 25 and 14 accessions, respectively (Figure 2). The second group consisted of eight accessions from Poland, two from Chile, two from Russia, one from the Netherlands, and one from Uruguay. These were generally the most resistant accessions largely corresponding to the PCA group of resistant genotypes. Some genotypes from the same countries with identical or very similar profiles could be seen, e.g., 502855 and 502856 as well as 502858 and 502859 from the United Kingdom or 51518 and 51630 from Poland.
For population structure analysis, the Bayesian model approach implemented in STRUCTURE software was used (Figure 3). The ΔK peak was the highest for K = 2, supporting the presence of two distinct populations. On the basis of the membership fraction, the accessions were categorized as homogeneous (probability ≥ 0.8) or admixed. P1 contained seven homogeneous accessions. In P2, fifteen homogeneous accessions were included. The remaining 17 accessions were classified as admixed. In general, P1 corresponded to resistance to most of the tested P. coronata race isolates, whereas P2 corresponded to susceptibility to these isolates. The analysis of the population structure in a graphical way refers to the results of the variation level within the accession obtained with the use of Shannon’s index and the coefficient of Nei’s diversity.

4. Discussion

The constant evolution of the P. coronata pathogen has caused the rapid loss of the effectiveness of the currently used crown rust resistance genes; therefore, the search for new ones is necessary. Wild oat progenitors have been proven to be a rich source of useful genes [32,33,35,52]; however, A. strigosa still remains unexploited. This study was carried out on 39 mostly European accessions from the Polish National Centre for Plant Genetic Resources with the majority originating from Poland (22 genotypes). A set of five P. coronata isolates was used to postulate the presence of potentially novel resistance genes.
Thirty-eight (97%) of the accessions studied showed a heterogeneous infection pattern; none of the accessions displayed homogeneous susceptibility, and only one, 51887, was homogeneously resistant to all P. coronata races. The heterogeneity of response to the rust inoculation within a single accession was already reported in the studies of wild oat species [32,33,53,54]; however, the level of phenotype variability within the analyzed A. strigosa was significantly higher, similar to the results obtained for A. fatua, where 85% of tested genotypes showed a heterogeneous infection pattern [31].
More than half of the A. strigosa genotypes screened in this research were characterized in terms of genetic (ISSR and SRAP), isoenzymatic, and morphological diversity by Podyma et al. [55,56]. According to Rodionova et al. [57], 17 botanical A. strigosa varieties can be distinguished based on clearly recognizable morphological traits. The results of the abovementioned authors revealed both genetic, botanical, and isoenzymatic variations in the analyzed objects. In terms of the morphology, within each accession, one to four varieties were recorded. Interestingly, within the most phenotypically variable A. strigosa accessions identified in our study (51586, 51520, 51523, and 51524), according to previous research, only one or two botanical varieties could be distinguished.
In this study, a detached leaf assay was used for resistance evaluation, allowing for the simultaneous testing of multiple rust isolates on a single plant. This is an important consideration when genotypes may be mixed as for many genebank accessions of landrace or previously uncharacterized material [35,58]. Additionally, the use of P. coronata races for the establishment of infection profiles (IP) allows postulating known and new Pc genes/alleles by matching the IPs of the tested plants with the profiles identified in differential lines. Twenty-eight infection profiles were defined within the 39 A. strigosa accessions, of which ten corresponded to the profile of known Pc genes. One hundred and sixty-eight out of 390 plants revealed an IP indicative of uncharacterized genes. Among the most resistant genotypes, 43 plants were immune to four of the five P. coronata races; each of these profiles corresponded to that of a highly efficient known Pc gene. However, this does not rule out that the identified profiles may correspond to new genes. To assess the genetic background of this resistance, it would be necessary to perform crosses with susceptible parents to determine the heredity model and conduct allelism tests to determine gene novelty.
Thirty-three plants within nine accessions were resistant to all crown rust races. A highly resistant response was shown by accessions 51578 from Uruguay and 51596 from Chile, with one plant in each resistant to all races and nine plants immune only to CR257. The most homogeneous accession was 51887 from Poland, resistant or moderately resistant to all isolates. According to the Polish Genebank, 51578 was acquired by the USDA (United States Department of Agriculture, Agricultural Research Service Small Grains Collection in Aberdeen, ID) in 1951 from the Instituto Fitotecnico y Semillero Nacional, Montevideo, and the equivalent of this number is PI 194201. This accession obtained from the USDA was tested by Admassu-Yimer et al. [59] for seedling resistance against eight P. coronata races. PI 194201 along with PI 193040, PI 237090, and PI 247930 were resistant to all the races used; however, according to USDA, all of the genotypes are classified as A. sativa. In the study of Podyma et al. [56], 51578 obtained from Polish genebank was assessed in terms of a range of morphological traits, and two A. strigosa varieties within the analyzed plants were recorded, which confirms the correct species classification. Both PI 194201 and 51578 exhibited high crown rust resistance; moreover, PI 194201, according to the GRIN database, possesses resistance to other important diseases of oats, including stem rust, barley yellow dwarf virus, and smut. The classification of both accessions should be reexamined; regardless, both could prove valuable for oat breeding programs. The equivalent number of 51596 from Chile is PI 436103. Apart from the crown rust resistance exhibited by this accession in this study, it displayed a high level of seedling resistance to five of six P. graminis races used in the study of Gold Steinberg et al. [26], which further increases the agronomic value of the genotype. The highest level of resistance was observed in 51887 acquired by the IHAR genebank in 1994 and classified as a Polish landrace. No further data regarding the resistance of this accession to other oat diseases are available, so it is worth conducting additional analysis, as previous studies indicate that the A. strigosa species can exhibit a wide range of resistance to various pathogens.

5. Conclusions

The results obtained in this research confirmed the complexity and heterogeneity of the accessions gathered in genebanks. Here, we compared the resistance within as well as between the accessions based on PCA and agglomerative hierarchical clustering. The generalized average of resistance across individuals from a given accession, standardly available in the genebank databases, may obscure the presence of individuals with significant resistance to pathogens and reduce interest in looking for new resistance sources within it. Even accessions with poor overall resistance, such as 51586, may contain very resistant and often overlooked plants. At a time when many available sources of oat resistance have been overcome, it might be worth looking for desirable traits within susceptible accessions, which could be hidden donors of effective pathogen resistance.

Author Contributions

Conceptualization and methodology, E.P.-G., S.S., and V.M.; investigation, E.P.-G.; resources E.P.-G.; writing—original draft preparation, S.S.; writing—review and editing, E.P.-G. and V.M.; visualization, S.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Conflicts of Interest

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

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Figure 1. Principal component analysis of the Avena strigosa L. accessions. A scatter plot of PC1 (explaining 41% of the variance) versus PC2 (explaining 11.3% of the variance). Label colors indicate the origin countries of the samples.
Figure 1. Principal component analysis of the Avena strigosa L. accessions. A scatter plot of PC1 (explaining 41% of the variance) versus PC2 (explaining 11.3% of the variance). Label colors indicate the origin countries of the samples.
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Figure 2. Ward’s dendrogram of 39 accessions of Avena strigosa L. The accessions were assigned with the numbers used in Table 1 and the colors indicating the origin countries of the samples used in Figure 1.
Figure 2. Ward’s dendrogram of 39 accessions of Avena strigosa L. The accessions were assigned with the numbers used in Table 1 and the colors indicating the origin countries of the samples used in Figure 1.
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Figure 3. Bar graphs showing the population structure of 39 accessions of Avena strigosa L. based on the resistance to five isolates of Puccinia coronata f. sp. avenae as assessed using STRUCTURE. Each population is represented by a different color.
Figure 3. Bar graphs showing the population structure of 39 accessions of Avena strigosa L. based on the resistance to five isolates of Puccinia coronata f. sp. avenae as assessed using STRUCTURE. Each population is represented by a different color.
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Sowa, S.; Mohler, V.; Paczos-Grzęda, E. Searching for Novel Oat Crown Rust Resistance in Diploid Oat Avena strigosa Schreb. Reveals the Complexity and Heterogeneity of the Analyzed Genebank Accessions. Agriculture 2023, 13, 296. https://doi.org/10.3390/agriculture13020296

AMA Style

Sowa S, Mohler V, Paczos-Grzęda E. Searching for Novel Oat Crown Rust Resistance in Diploid Oat Avena strigosa Schreb. Reveals the Complexity and Heterogeneity of the Analyzed Genebank Accessions. Agriculture. 2023; 13(2):296. https://doi.org/10.3390/agriculture13020296

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Sowa, Sylwia, Volker Mohler, and Edyta Paczos-Grzęda. 2023. "Searching for Novel Oat Crown Rust Resistance in Diploid Oat Avena strigosa Schreb. Reveals the Complexity and Heterogeneity of the Analyzed Genebank Accessions" Agriculture 13, no. 2: 296. https://doi.org/10.3390/agriculture13020296

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