Introduction

Spelt wheat (Triticum spelta L.) is considered to be an ancient European wheat, and it was one of the main crops from the Bronze and Iron Age up to the Middle Ages in western Austria, Switzerland and southwestern Germany (Rösch et al. 1992; Lechterbeck and Kerig 2024). Thereafter, spelt was continuously replaced by higher yielding landraces of common wheat (T. aestivum L.) and despite the installation of first breeding programmes in Germany and Switzerland at the turn of the twentieth century its cultivation in Europe nearly disappeared (Grausgruber 2018). Spelt came back in the 1970s with an increased interest in a healthy lifestyle and the development of organic farming (Longin and Würschum 2016; Alvarez 2021) as this wheat (sub)species was always associated with being more nutritious, less input demanding and more tolerant to biotic and abiotic stresses. Compared to common wheat, spelt achieves lower grain yields and requests additional processing (i.e. dehulling). Thus, spelt products are generally more expensive.

A significant advantage of spelt is its tolerance to adverse climatic and soil conditions, which predetermines it to be grown in organic farming. Some spelt accessions were also used as sources of disease resistance in the development of common wheat germplasm. Resistance to fungal diseases is a prerequisite for varieties cultivated in organic agriculture as their control by pesticides is forbidden, and organic plant protection is often limited, or as in case of foliar copper fungicides, there is concern over the toxicity and persistence of residues (Edward-Jones and Howells 2001).

Common bunt (Tilletia caries and T. laevis) is a seedborne disease that causes significant losses in grain yield and end-use quality. The use of healthy (certified) seed and/or seed treatment by effective fungicides is essential to avoid outbreaks of common bunt. In organic farming, additional preventive measures include seed analysis, brush-cleaning of seeds, crop rotation, inspections of crop stands, seed treatment with products registered for organic farming and, certainly, the use of resistant varieties (Goates 1996; Matanguihan et al. 2011).

Stem rust (Puccinia graminis f. sp. tritici) re-emerged in European countries to a greater extent in 2016 and 2017. These occurrences indicate a possible spread of the disease in near future. The potential harmfulness of stem rust in case of an epidemic is very high, resulting in up to 80% yield losses. More frequent occurrences are related to the spread of new races of stem rust and its variants (Singh et al. 2015). Spelt wheat may be a valuable source of resistance genes, for instance, McVey and Leonard (1990) identified more than 20 new Sr genes in spring spelt accessions of the USDA National Small Grains Collection. Yellow rust (P. striiformis f. sp. tritici) may also cause yield losses in the range of 60–70% during epidemic occurrences. In Europe, since 2000, there have been frequent changes in the yellow rust population. The original population has been largely replaced by new races. These new races are adapted to higher temperatures, which leads to the expansion of yellow rust to areas previously unaffected by infection (Hovmøller et al. 2016; Ali et al. 2017). Spelt wheat is a source of yellow rust resistance genes Yr5 and Yr10 which were detected in var. album (Macer 1966; Kema 1992) and line 415 from Iran (Kema and Lange 1992), respectively. Leaf rust (P. triticina) causes high yield losses due to regular widespread occurrences. It is especially harmful in dry, hot years. When growing susceptible varieties and with higher infection pressure, the yield can be reduced by up to 50% (Samborski 1985; Huerta-Espino et al. 2011). Resistance genes Lr44, Lr65 and Lr71 were identified in spelt line 7831 from Spain (Dyck and Sykes 1994) and variety ʻAltgoldʼ from Switzerland (Wang et al. 2010; Mohler et al. 2012; Singh et al. 2013), respectively.

Powdery mildew (Blumeria graminis f. sp. tritici) is a serious foliar disease of wheat causing significant yield losses up to 20–40% especially if the flag leaf and the ear are affected at early stages, i.e. head emergence (Johnson et al. 1979; Conner et al. 2003). In case of a heavy and early attack, yield losses are mainly due to a decrease in grain weight. Resistance allele Pm1d was found in T. spelta var. duhamelianum (Hsam et al. 1998), and a recessive resistance gene to powdery mildew was located on chromosome 2D of Swiss variety ʻHubelʼ (Peng et al. 2014). Another QTL for adult-plant resistance was detected on chromosome 5A of Swiss spelt variety ʻOberkulmerʼ (Keller et al. 1999). The occurrence of powdery mildew is supported by higher temperatures and nitrogen fertilisation rates (Last 1953), therefore, less a problem in organic agriculture compared to conventional high-input agriculture.

The leaf blotch disease complex (Septoria tritici blotch, Zymoseptoria tritici; Septoria nodorum blotch, Parastagonospora nodorum and tan spot, Pyrenophora tritici-repentis) induces major yield losses in wheat worldwide. The occurrence of the three fungi is influenced by crop rotation and tillage methods as the fungi survive and form pseudothecia on plant debris. The occurrence of mixed infections is common and widespread, resistance against all three leaf blotch diseases is rarely available in high-yielding varieties, and therefore, control by fungicides is common practice. However, fungicide resistance by mutations of the pathogens and increasing adverse regulatory framework for widely used active ingredients will make resistance breeding a major driver for sustainable wheat production (Singh et al. 2016; Garnault et al. 2021; Justesen et al. 2021). New sources of resistance against leaf blotch diseases of wheat have been identified in spelt (Singh et al. 2006). Partial resistance to Septoria tritici blotch was found in line 69Z6.886 from Spain (Kolomiets et al. 2017). A quantitative resistance to some Septoria tritici blotch isolates was mapped in spelt wheat to chromosome 7D (Simon et al. 2010). Four QTL for resistance to tan spot have been identified by Karlstedt et al. (2019) in the German landrace ʻZeiners Schlegeldinkelʼ.

Resistance of spelt wheat to Fusarium head blight (caused mainly by Fusarium graminearum and F. culmorum) and its most important mycotoxin deoxynivalenol was investigated by Chrpová et al. (2021). A total of 16 genotypes were classified as resistant to Fusarium head blight, and it was found that typical spelt traits such as tall plant height, lax spikes and tough glumes play a role as passive resistance factors.

The aim of the present study was the evaluation of a spelt wheat diversity panel including historic and current European winter spelt germplasm for its resistance against wheat rusts, powdery mildew, the leaf blotch complex and common bunt.

Materials and methods

Plant material

Eighty spelt wheat genotypes were selected to represent a diversity panel of European winter spelt germplasm including landraces, old and obsolete varieties as well as modern varieties and breeding lines. The material was grouped into (i) ʻLRʼ consisting of old varieties from Switzerland and Germany (or selected from landraces/old varieties such as ʻRubiotaʼ, registered 1981 in Czechia; ʻEbners Rotkornʼ, registered 1999 in Austria and ʻÖko 10ʼ, registered 2000 in Hungary); (ii) ʻCVʼ representing modern varieties (post-1970) from Switzerland, Germany and Belgium and (iii) ʻPGRʼ including plant genetic resources and genebank accessions of uncertain breeding status. The diversity panel was already evaluated before for resistance to Fusarium head blight (Chrpová et al. 2021).

Field experiments

Field experiments have been carried out in Austria (Raasdorf and Tulln), Czechia (Prague), Estonia (Jõgeva), Germany (Darmstadt) and Switzerland (Rheinau: natural occurence of rust; artificial infection with rust spreaders in Mesikon 2015, Seegräben 2016 and Fehraltorf 2017 and common bunt trials in Stäfa 2016, Feldbach 2017 and Lützelsee 2018). The whole diversity panel was evaluated from 2013 to 2017 resulting in 12 environments for powdery mildew, 18 for yellow rust, 19 for leaf rust, 3 for stem rust, 6 for leaf blotch and 8 for common bunt. Twenty genotypes were selected for additional testing from 2018 to 2019 in a hulled (four environments) and dehulled status (three environments) for resistance to common bunt (Table 1). The genotypes were randomly selected to represent different levels of disease incidence in hulled and dehulled status seen in the previous years. One or two rows were evaluated for natural infection (powdery mildew, rusts and leaf blotch) or artificial infection according to the method used in the respective test environment. Inoculum for artificial infection consisted of the locally most prevalent pathotypes, applied through an inoculated spreader variety (rusts) or seed inoculation by shaking with a surplus of teliospores (common bunt). Scoring of the leaf diseases has been carried out on 1–9 scale (9 = severe infection), modified after Saari & Prescott (1975). For common bunt, the genotype’s reaction was expressed as percentage of spikes exhibiting bunt. For the identification of races, an infection incidence above 10% of the spikes indicates virulence (Goates 1996). Additionally, plant height was measured from the ground to the top of the spike excluding awns if present.

Table 1 Environment (location × year) means for disease reaction of the HealthyMinorCereals spelt (Triticum spelta) diversity panel
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PCR detection of leaf rust and stem rust resistance genes

Susceptible genotype T. spelta Kromeriz and 16 genotypes showing the least susceptible response in the field trials were analysed for rust resistance genes using available molecular markers, currently used at CRI for winter wheat screening. Genomic DNA was isolated from the youngest leaves of 20–30 plants per genotype. Leaf tissue was frozen in liquid nitrogen, ground to a powder and used for DNA extraction by commercial kit (Qiagen, Germany). Polymerase chain reaction (PCR) protocols used for corresponding markers for genes Lr1, Lr9, Lr10, Lr19/Sr25, Lr24/Sr24, Lr28, Lr34/Sr57/Yr18, Lr37/Sr38/Yr17 and Sr6 are listed in Table 2. The gene complexes were originally transferred from wheat wild relatives to bread wheat (McIntosh et al. 1995) and may be present in modern spelt varieties because of spelt × bread wheat crosses largely deployed in spelt breeding programmes in Belgium, Germany and Switzerland since the 1970s (Grausgruber 2018). PCR was performed in the thermal Labcycler (SensoQuest GmbH, Germany). Amplification products were separated by electrophoresis on 1.6% agarose gels stained with ethidium bromide and visualised under UV light. GeneRulerTM 100-bp DNA Ladder (Fermentas, Lithuania) was used as a molecular weight marker.

Table 2 Molecular markers used in PCR assays to indicate the presence of resistance genes
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Statistical analysis

Normal distribution of data was tested by the Shapiro–Wilk test, genetic groups were compared according to the Tukey’s HSD test, correlation analyses and statistical graphs were carried out in Statistica 14.0.0.5 (TIBCO Software Inc., Palo Alto, CA). Linear mixed model analysis of variance for each disease was performed with the lme4 (v. 1.1–31) package (Bates et al. 2015) of R software (R Foundation for Statistical Computing, Vienna, Austria). All models were fitted using restricted maximum-likelihood estimation (REML) and the default settings. Genotypes were considered as fixed effect; location, year and replication as random effects. The replication effect was nested within the ‘environment’ (location × year). In case of stem rust, only one location and one replication were available; therefore, only the year effect was considered. Best linear unbiased estimators (BLUEs) were calculated for genotypes in each analysis.

Results

The highest environmental mean for common bunt incidence was 13.5% in the hulled variant (nE = 10) and 55% in the dehulled variant (nE= 5) (Table 1). Leaf blotch highest mean score was 4.1 (nE = 6); powdery mildew highest mean score was 6.6 (nE = 12); leaf rust highest mean score was 8.9 (nE = 19); stem rust highest mean score was 8.7 (nE = 3) and yellow rust highest mean score was 5.3 (nE = 18). Environments with too many missing values were excluded from the calculation of BLUEs (Fig. 1).

Correlations between plant height and disease severity were all extremely low and/or not significant: common bunt (r = − 0.10; p = 0.373); leaf blotch (r = − 0.20; p < 0.001); powdery mildew (r = − 0.003; p = 0.925); leaf rust (r = 0.11; p < 0.001); stem rust (r = 0.12; p = 0.073) and yellow rust (r = 0.06; p = 0.017).

Fig. 1
figure 1

Genotypic variation of spelt in the disease score across the test environments: a PM, powdery mildew score of visual symptoms (1–9); b LB, leaf blotch score of visual symptoms (1–9); c LR, leaf rust score of visual symptoms (1–9); d YR, yellow rust score of visual symptoms (1–9); e CB, common bunt incidence (% of bunted ears); environments with an asterisk indicate trials with dehulled seeds and f SR, stem rust score of visual symptoms (1–9). Cross symbols represent mean values; boxes represent the lower quartile, median and upper quartile; whiskers are drawn to the lower and upper extreme within the ± 1.5 × IQR area and circles represent outliers

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Common bunt

Common bunt incidence usually fluctuates to some extent from year to year even in carefully conducted trials with artificial infection; however, in our trials, the presence of hulls was the most important influencing factor. The dehulled variant had a higher common bunt incidence and revealed that most genotypes tested do not carry effective genes for resistance. For the hulled variant, most of the obtained environmental means did not exceed 10% (Table 1), indicating that the hulls provide some mechanical protection from infection. The means of common bunt incidence for a subset of 20 genotypes in a hulled and dehulled variant show clearly a higher attack in the hulled variant (Fig. 2). The correlation for all 80 genotypes in hulled and dehulled variant (r = 0.56) was significant (p < 0.001) (Fig. 3). It is important to know that genetic variation exists with respect to the tightness of the hulls which may affect the level of infection and thus the strength of correlation.

Fig. 2
figure 2

Difference in common bunt (CB) incidence of the subset of 20 spelt genotypes after artificial inoculation of a hulled and b dehulled seeds. Cross symbols represent mean values; boxes represent the lower quartile, median and upper quartile; whiskers are drawn to the lower and upper extreme within the ± 1.5 × IQR area and circles represent outliers

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Fig. 3
figure 3

Relationship between common bunt (CB) incidence in the hulled vs. dehulled variant. Linear regressions and confidence bands (α = 0.05) were fitted to all data

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‘Sofia 1’ and ‘Albin’ showed very low disease severity in all eight environments (Table 3 and Table S1), both in the hulled and dehulled status. Considering a cutoff of 10%, the other genotypes with a low level of common bunt infection were ‘T. spelta Kromeriz’, ‘Altgold’, ‘Ceralio’, ‘Gugg 2G’, ‘Badengold’ and ‘Spy’. However, genotypes ‘Tauro’, ‘Gugg 6A’, ‘Toess 5B’ and ‘LW12 Nürtingen’ would also fall into the category of resistant genotypes based on the common bunt incidence lower than 10% of ears. Genotypes ‘T. spelta Kromeriz’, ‘Altgold’, ‘Ceralio’, ‘Gugg 2G’, ‘Gugg 6A’, ‘LW12 Nürtingen’ and ‘Badengold’ proved resistant reaction in the hulled variant, but in the dehulled variant, they had a susceptible reaction exceeding 10% of bunted ears. In the group of genotypes ‘Spy’, ‘Tauro’ and ‘Toess 5B’, there were occurrences in individual environments with more than 10% even in the hulled variant. The 10% genotypes with the highest susceptibility were ‘T. spelta album Tabor’, ‘Vögeles Dinkel weiß’, ‘Cosmos’, ‘Strickhof’, ‘Samir’, ‘Black Forest’, ‘Speltvete från Gotland’ and ‘Schwabenspelz’.

Table 3 Best linear unbiased estimators and rating of genotypes
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Leaf blotch

Leaf blotch was common and has occurred to some degree in all environments but no serious incidence was recorded (Table 1). Genotypes ‘Sofia 1’, ‘Riniken Weißkorn’, ‘Zürcher Oberländer Rotkorn’, ‘Alkor’, ‘Gugg 11A’, ‘Gugg 2F’, ‘Gugg 5C’ and ‘Toess 5B’ were among the most resistant 10% (Table 3 and Table S1). However, there were a total of 64 genotypes with resistant reaction according to their mean disease score between 1 and 3. ‘Sofia 1’, ‘Riniken Weißkorn’, ‘Zürcher Oberländer Rotkorn’ and ‘Toess 5B’ showed resistant reaction in all environments. Individual cases of environments with disease score 4, i.e. moderately resistant (MR), appeared in varieties ‘Alkor’, ‘Gugg 11A’, ‘Gugg 2F’ and ‘Gugg 5C’. The 10% genotypes with the highest susceptibility were ‘Rosén (Sel.)’, ‘Hercule’, ‘Albin’, ‘Cosmos’, ‘Holstenkorn’, ‘Poeme’, ‘Badenkrone’ and ‘Von Rechbergs Früher Winterspelz’.

Powdery mildew

Environmental fluctuations in powdery mildew with both low and higher incidence were observed. The highest disease pressure was observed in the Austrian site Raasdorf, characterised by warmer temperatures in spring compared to the other environments. Lowest disease pressure was recorded for the organically managed Swiss environments. Mean disease scores in the range between 1 and 3, which means resistant reaction (R), occurred in a total of 47 genotypes (Table 3 and Table S1). The 10% genotypes with the lowest disease score were ‘Speltvete från Gotland’, ‘T. spelta Kromeriz’, ‘Epanis’, ‘Gugg 11A’, ‘Lonigo’, ‘Black Forest’, ‘Gugg 6A’ and ‘Sofia 1’. They were resistant according to their mean values, although each genotype showed a higher rating (5–6) in at least one environment. The 10% genotypes with the highest susceptibility were ‘Muri Rotkorn’, ‘Rottweiler Frühkorn’, ‘Gugg 5A’, ‘Schwabenspelz’, ‘Von Rechbergs Brauner Winterspelz’, ‘Hercule’, ‘Vögeles Dinkel weiß’ and ‘Gugg 4E’.

Stem rust

There were only three evaluations and one single location for stem rust evaluation, i.e. CZ_Pr15, CZ_Pr16 and CZ_Pr17, but the plant damage was the most serious one of all monitored diseases (Fig. 4). The vast majority of genotypes were highly susceptible (Table 4 and Table S1). Resistant was ‘Sofia 1’, moderately resistant was ‘Samir’, then already susceptible, but slightly better than the other susceptible genotypes was ‘Lonigo’ with a mean disease score 6.7 and the rest of the 80 genotypes was highly susceptible. In 25 cases, the mean score had the highest possible value of 9. None of the stem rust resistance genes analysed by molecular markers were assumed either in resistant ‘Sofia 1’ or in moderately resistant ‘Samir’. They may carry resistance genes for which we did not have markers available or even some undescribed genes.

Fig. 4
figure 4

Heatmap of the resistance performance of the spelt diversity panel. Green cells indicate resistant, orange cells indicate susceptible genotypes (top and worst 10%, respectively, for all diseases except stem rust). CB, common bunt; LB, leaf blotch complex; PM, powdery mildew; LR, leaf rust; YR, yellow rust and SR, stem rust

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Table 4 Best linear unbiased estimators and rating of genotypes
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Leaf rust

Leaf rust incidence was often high, low occurrences were rather rare and observed more in the Czech and Estonian environments. Contrary to powdery mildew, organically managed trials (i.e. Germany and Switzerland) did not exhibit a lower disease severity (Table 1). The 10% genotypes with the lowest disease score were ‘Sofia 1’, ‘Spy’, ‘Epanis’, ‘Black Forest’, ‘Filderstolz’, ‘Farnsburger Rotkorn 6’, ‘Gugg 4H’ and ‘Fuggers Babenhauser Zuchtvesen’ (Table 4 and Table S1). There were a total of 12 varieties with resistance to rust, including ‘Rottweiler Dinkel St. 6’, ‘Badenkrone’ and ‘Öko 10’. Only for ‘Sofia 1’, the maximum score in individual environments never exceeded 6; otherwise, disease score of 9 appeared at least once in the individual genotype evaluations. The 10% genotypes with the highest susceptibility were ‘Elsenegger Weißkorn’, ‘Burghof’, ‘Winiger-Egg Weißkorn 19’, ‘Burgdorf Weißkorn 1’, ‘Frienisberger Weißkorn 49’, ‘Vorrenwalder Weißkorn 15’, ‘Gugg 9A’ and ‘Ruefenacher Weißkorn 6’.

In the 16 genotypes showing the least susceptible response to leaf rust in the field trials, the resistance genes Lr1 and Lr10 are present according to the applied molecular markers: ‘Sofia 1’, ‘Spy’ and ‘Badenkrone’ (Lr1); ‘Filderstolz’ and ‘Rottweiler Dinkel St. 6’ (Lr10); ‘Epanis’, ‘Farnsburger Rotkorn 6’, ‘Fuggers Babenhauser Zuchtvesen’, ‘Gugg 4H’ and ‘Öko 10’ (Lr1, Lr10) and ‘Black Forest’ (Lr10) (Table 5). Genes Lr9, Lr19/Sr25, Lr24/Sr24, Lr28, Lr34 and Lr37/Sr38 are not present in the tested diversity panel.

Table 5 Wheat leaf rust, stem rust and yellow rust resistance genes identified in a subset of 16 genotypes showing the least susceptible response in the field trials using molecular markers
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Yellow rust

Disease severity of yellow rust varied significantly between environments. Both low infestations as well as devastating occurrences were recorded even within the same location in different years. ‘Speltvete från Gotland’ showed very low disease severity in all environments (Table 4 and Table S1). Other genotypes showed in at least one environment a susceptible disease score 5. The 10% genotypes with the lowest disease score were ‘Speltvete från Gotland’, ‘T. spelta album Tabor’, ‘Holstenkorn’, ‘Lonigo’, ‘T. spelta Svetla’, ‘Gugg 4E’, ‘Zuzgen 15A’ and ‘Zeiners Weißer Schlegeldinkel’. There were a total of 69 varieties with resistant reaction according to their mean disease score in the range of 1–3. The 10% genotypes with the highest susceptibility were ‘Muri Rotkorn’, ‘Ostro’, ‘Tauro’, ‘Öko 10’, ‘Ebners Rotkorn’, ‘Zürcher Oberländer Rotkorn’, ‘Filderstolz’ and ‘Samir’.

Breeding period

The influence of the breeding period on the mean disease severities is shown in Table 6. The proportion of susceptible genotypes in the individual groups was different for the various diseases studied (Table 7). Modern spelt varieties showed a higher susceptibility to leaf blotch compared to old landraces. The proportion of susceptible genotypes in modern varieties was 14.3% compared to only 2.2% in old landraces and varieties. The 10% genotypes with the lowest leaf blotch incidence were mainly from the group of old landraces. Modern varieties have also shown a higher susceptibility to yellow rust than old landraces. The proportion of susceptible genotypes in modern varieties was 14.3%, whereas in old landraces and varieties, it was only 2.2%. The 10% genotypes with the lowest yellow rust incidence were mainly from the group of plant genetic resources. On the contrary, higher resistance to common bunt was observed in modern varieties. In this case, 91.1% of old landraces and 76.2% of modern varieties were susceptible. However, the 10% genotypes with the lowest incidence were mainly from the old landraces group. Resistance to leaf rust was more frequent in modern varieties. The proportion of susceptible varieties in old landraces was with 53.3% significantly greater compared to 23.8% in modern varieties. In the 10% genotypes with the lowest incidence, the number of old landraces and modern varieties was equal. The response of old landraces to powdery mildew did not differ from modern varieties; 4.8% of modern varieties and 4.4% of old landraces were susceptible. The 10% genotypes with the lowest incidence were mainly from the group of plant genetic resources. ‘Samir’ was the only modern variety with moderate resistance to stem rust. None of the landraces was resistant to stem rust. Resistant genotype ‘Sofia 1’ is grouped into the plant genetic resources as its origin and breeding history is unclear.

Table 6 Best linear unbiased estimators (BLUEs) for disease incidence of spelt germplasm from different breeding periods
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Table 7 Frequency and number of genotypes admitted to disease rating groups of spelt germplasm from different breeding periods
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Some genotypes appeared in the 10% with lowest disease score more than once, and thus, they have shown multiple disease resistance (Table 7). ‘Sofia 1’ showed resistance even to five diseases. It was the most resistant genotype for common bunt, leaf blotch, leaf rust and stem rust, and it belonged to the best 10% for powdery mildew. ‘Sofia 1’ previously showed also lower disease severity in field trials with Fusarium head blight (Chrpová et al. 2021). Other varieties with low diseases severity for two diseases at the same time were ‘Speltvete från Gotland’ and ‘Lonigo’ for powdery mildew and yellow rust, ‘Epanis’ and ‘Black Forest’ for powdery mildew and leaf rust, ‘Spy’ for common bunt and leaf rust, ‘Gugg 11A’ for powdery mildew and leaf blotch and ‘T. spelta Kromeriz’ for powdery mildew and common bunt.

Discussion

Generally, only a few studies are available which could be compared with our results and almost all studies hitherto carried out were done with only a limited number of genotypes. Spelt wheat is often mentioned and regarded as tolerant against diseases and adverse conditions; however, Longin and Würschum (2014) reported that susceptibility to leaf rust, powdery mildew and septoria tritici blotch in spelt was similar or even higher as compared with current bread wheat varieties. They observed in their diversity panel comprising landraces, old and new varieties mean values of 5.5 for leaf rust, 3.2 for powdery mildew and 3.4 for septoria tritici blotch. The estimates for disease incidence in the groups of landraces and old varieties (LR) and modern varieties (CV) in our study were similar: slightly lower for leaf rust (5.3 and 4.6, respectively), slightly higher for powdery mildew (4.1 and 3.9, respectively) and slightly higher for leaf blotch (3.5 and 3.9, respectively). The negative correlation between susceptibility to septoria tritici blotch and plant height observed in spelt by Longin and Würschum (2014) could not been confirmed by our study. It is well known that a tall plant height of wheat may be responsible for a disease escape of vertically spreading diseases such as septoria tritici blotch. For several genotypes, the tolerance to diseases was similar in both our study and the study of Longin and Würschum (2014): ‘Epanis’ showing the lowest scores for powdery mildew; ‘Spy’, ‘Epanis’ and ‘Gugg 4H’ showing the highest resistances against leaf rust and ‘Gugg 5C’, ‘Samir’ and ‘Alkor’ showing a low incidence of leaf blotch complex. A subset of 123 spelt lines from the spelt panel of Longin and Würschum (2014) was genotyped by a wheat SNP array, and a genome-wide association mapping was applied by Würschum et al. (2017). Mainly small effect QTL were identified; however, also two major putative QTL for leaf rust, two for powdery mildew and one for septoria tritici blotch were found. Würschum et al. (2017) showed that there is no major population structure and no grouping according to the age of the tested germplasm, most probably due to the short breeding history of spelt and the intensive use of landraces and old varieties in the past 50 years of spelt breeding in Central Europe.

Aguilar et al. (2005) described high level of resistance against septoria nodorum blotch on the ear and medium resistance on the leaf in the Swiss landrace selection ‘Oberkulmer’. Its most important QTL for resistance was associated with the q locus conferring the typical speltoid ear morphology. Leaf blotch incidence of ‘Oberkulmer Rotkorn’ was also low in our study. A very lax ear morphology and long uppermost internode leads to a less humid microclimate which is less favourable for septoria nodorum blotch. Hard glumes and thick wax layer are mechanical barriers, preventing the penetration of the pathogen. A lower susceptibility to the leaf blotch complex was also reported for two Canadian spelt wheat varieties compared to common and durum wheat varieties. A very low incidence of tan spot was found by Tadesse et al. (2011) for ‘Ceralio’ which had also a very low incidence of leaf blotch complex in our study.

A difference between hulled and dehulled seeds in relation to common bunt infection was observed previously for ‘Rubiota’ and ‘Franckenkorn’ (Dumalasová and Bartoš 2010). According to the results obtained with the hulled variant of 20 genotypes in this study, it seems that spelt seed has less of a problem with common bunt compared to winter wheat. However, after inoculation of dehulled seed it turns out, that not Bt genes present in spelt are responsible for the lower disease incidence but a protection mechanism of the hulls. Hence, to study the presence of resistance genes to the common bunt in spelt, dehulled seed should be used to obtain reliable results. It is also important to keep in mind, that the hulls will not limit dwarf bunt infections, as in this case, the infection happens at later stages of development after crop emergence when the hulls no longer play a role.

Schachermayr et al. (1997) described two markers for leaf rust resistance gene Lr10 and detected the gene in ‘Oberkulmer’ and ‘Ostro’ which originated from a cross with ‘Oberkulmer’. In our study, these two varieties were evaluated moderately resistant with estimates of 4.8 and 4.1, respectively. Goriewa-Duba et al. (2020) analysed breeding lines derived from crosses between spring bread and spring spelt wheat and their parental genotypes. Lr10 and Lr28 were confirmed for three and one parental spelt line out of five, respectively. In our study, Lr10 was prevalent, being present in 10 out of 16 genotypes, while Lr28 was not identified in the tested germplasm. Lr28 was originally transferred from Aegilops speltoides to spring common wheat (McIntosh et al. 1995). Goriewa-Duba et al. (2020) do not unravel the origin of their spelt line S10 carrying this resistance gene; however, it may be assumed that it already derived from a cross with bread wheat. Similarly, the Lr37/Yr17/Sr38 resistance gene complex was initially introgressed in bread wheat from Aegilops ventricosa (Maia 1967). In bread wheat, Lr37 occurs very frequently in common wheat genotypes; however, it was not detected in our study. This does not imply that our tested germplasm does not contain any bread wheat in its pedigree—as it is definitely known that a few varieties were derived from crosses with bread wheat—but only that the Ventriup/Ln2 locus was not detected in any of the used bread wheat progenitors. The low presence of effective resistance genes in spelt and bread wheat against new races poses a high risk for wheat cultivation in case of a further spreading of new aggressive races. A similar situation is existing for leaf rust. High infestations with leaf rust were observed in our study in many environments, indicating that under suitable conditions, a devastating occurrence on spelt may occur. Resistance genes Lr1 and Lr10 were found with a high frequency in the tested spelt genotypes; these genes are not very effective anymore when deployed alone, but may play a role in combinations of several Lr genes (McIntosh et al. 1995). Hanzalová et al. (2020) also have shown that 78% of the Czech leaf rust isolates are virulent to Lr1, and 91% of the isolates are virulent to Lr10. Since in the tested germplasm, resistant spelt genotypes were identified, the presence of other resistance factors not revealed by the applied molecular markers highly likely. These unspecified resistance factors may include both race-specific genes (R-genes) and race-nonspecific adult-plant resistance (APR).

Conclusion

The risk of fungal diseases in spelt is non-negligible. Based on our results, we conclude that rust diseases may pose a threat to spelt cultivation, while no serious incidence was recorded for the leaf blotch disease complex in our test environments. No considerable difference in the susceptibility to diseases has been generally observed between modern and landraces/old varieties; hence, both variety types have their authorisation for cultivation from a phytopathological point of view. A special problem in spelt is common bunt as bunted ears and/or spikelets are masked until the dehulling process and then contaminate seriously the dehulling devices and healthy seeds. The majority of spelt genotypes are highly susceptible to common bunt; however, if spelt is sown as hulled seed, the hulls act as mechanical barrier to the bunt spores on the outer surface of the hulls. Hence, sowing spelt in hulls may have some disease escape effect in case of common bunt despite the difficulties in adjusting sowing machines and sowing densities. Generally, an acceptable level of disease resistance against fungal diseases is present in spelt. Some genotypes showed a very low disease infestation in all environments tested, ‘Sofia 1’ and ‘Albin’ for common bunt, ‘Sofia 1’, ‘Riniken Weißkorn’, ‘Zürcher Oberländer Rotkorn’ and ‘Toess 5B’ for leaf blotch, ‘Sofia 1’ for leaf and stem rust and ‘Speltvete från Gotland’ for yellow rust. Multiple resistance has been identified for ‘Sofia 1’. This genetic resource may be used in future spelt breeding programmes for the development of resistant varieties which is of special importance in organic farming where spelt is especially popular.