Annals of Applied Biology ISSN 0003-4746 REVIEW ARTICLE Aspects in oat breeding: nutrition quality, nakedness and disease resistance, challenges and perspectives A. Gorash1 , R. Armonienė1 , J. Mitchell Fetch2 , Ž. Liatukas1 & V. Danytė1 1 Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry, Akademija, Lithuania 2 Agriculture and Agri-Food Canada, Brandon Research and Development Centre, Brandon, Manitoba, Canada Keywords Avena sativa L.; disease resistance; naked oat; oat agronomy; oat breeding. Correspondence A. Gorash, Institute of Agriculture, Lithuanian Research Centre for Agriculture and Forestry, Instituto 1, LT-58344 Akademija, Kėdainiai, Lithuania. Email: andrej@lzi.lt Received: 19 October 2016; revised version accepted: 28 June 2017. doi:10.1111/aab.12375 Abstract Traditionally, the oat crop (Avena sativa) has been neglected in a number of respects, cultivated in cropping areas not optimal for wheat, barley or maize. In recent years the interest in oats has increased, particularly because of its dietary benefits and therapeutic potential for human health. The uniqueness and advantages of naked oats over other popular cereals, due to its potentially valuable nutritional composition, have been well studied and reported, opening new market “niches” for oats. Despite the well-documented benefits, the status of the oat crop is still fragile, due to many reasons. The area cultivated for the oat crop is much less compared with other cereals, and therefore commercial efforts in oat breeding are less. Oat groat yield is lower than other cereals such as wheat and the nutritious uniqueness has not been reflected in agreeable market prices. The same price still exists for both naked and conventional/covered oats in the world grain market. The absence of visible market competitiveness, and some of the oat biological drawbacks, including low grain yield, keeps the oat crop as a lower profitability minor crop. This review is intended to analyse and summarise main achievements and challenges in oat genetics, agronomy and phytopathology to find possible ways of oat improvement and future perspectives for oat breeding. Introduction The genus Avena includes about 70 species, many of which are commercially cultivated. Most oats under production worldwide belongs to the hexaploid species: Avena sativa L. (white oats, the most important cultivated oat) (2n = 6x = 42. AACCDD) and Avena byzantina C. Koch (red oats, grown in warmer climates generally as a winter oat) (2n = 6x = 42. AACCDD). Other cultivated species with minor, regional importance include Avena abyssinica Hochst. (Ethiopian Oats) (2n = 4x = 28, AABB), Avena strigosa Schreb. (known by several common names such as Lopsided, Bristle, Sand or Black Oats) (2n = 2x = 14, AsAs) and Avena nuda L. (Naked Oat or Hulless Oat) (2n = 2x = 14, AsAs). Diploid naked oats, Avena nuda L., are not commonly cultivated, and are predominantly grown at high altitudes in China. Naked types of oats occur in several oat species. Most of the commercially grown naked cultivars belong to the hexaploid species, Ann Appl Biol (2017) © 2017 Association of Applied Biologists Avena sativa (Reynolds, 2004; Gazal et al., 2014; Menon et al., 2016). In recent decades, the discussion on oat grain dietetic value and suitability for the production of functional food has increased in public and scientific literature. A large and growing body of literature has documented its dietary benefits for health and therapeutic potential (Biel et al., 2009; Daou & Zhang, 2012; Clemens & van Klinken, 2014). It is well known that oats can be used for preventive/therapeutic health care in the treatment of such diseases as coronary heart disease (Mellen et al., 2008; Thies et al., 2014a; Nwachukwu et al., 2015; Schuster et al., 2015) through the reduction of serum cholesterol and control of obesity (Chen et al., 2006; Zdunczyk et al., 2006; Chang et al., 2013; Shebini El et al., 2014; Whitehead et al., 2014; Nwachukwu et al., 2015). Consumption of oat may aid in treatment of Type II diabetes, through stabilisation of blood sugar levels (Tapola et al., 2005; Priebe et al., 2008; Zhang et al., 2014; Ho, 2015; 1 Aspects in oat breeding Hou et al., 2015), and certain cancers (Egeberg et al., 2010; Boffetta et al., 2014; Clemens & van Klinken, 2014; Thies et al., 2014b). Oats have superior and unique combinations of nutrients: high protein content (12.4%–24.4%) with beneficial composition of amino acids, soluble and insoluble dietary fibre (2.85%–12%), including 𝛽-glucan, and rich in fat (2%–12%) (Peterson, 2004; Redaelli et al., 2013; Rasane et al., 2015; Menon et al., 2016). 𝛽-glucan in humans is involved in natural defence against infections caused by viruses, bacteria and fungi, and in reduction of glucose and cholesterol levels in the blood (Queenan et al., 2007; Brindzová et al., 2008; Rondanelli et al., 2009; Djukic & Kneževic, 2014). Numerous studies have reported that oats are an excellent source of antioxidants (Peterson, 2001; Rasane et al., 2015; Van den Broeck et al., 2016). The 𝛽-glucan in oat differs from 𝛽-glucan of barley and wheat in many physicochemical properties, such as solubility, gelation and molecular weight, all of which positively affect physiological functions in the gastrointestinal tract. These particular properties of 𝛽-glucan may explain the connection between oat consumption and lowering of serum cholesterol levels (Chu, 2014). The oat crop differs from other cereals (wheat, barley and rye) because it contains a higher proportion of salt–water soluble globulin, whereas most of the other cereals contain higher proportions of prolamins (the alcohol–soluble fraction). Oat protein provides a better balance of most essential amino acids for humans and other monogastric mammals (Givens et al., 2004; Biel et al., 2009; Klose & Arendt, 2012; Chu, 2014). The levels of crude fat in oats are much higher than those of other cereal grains, giving oats prevalence for livestock feeding by supplying more calories (metabolisable energy). Some authors made predictions that oats could be used for industrial oil extraction (Zhou et al., 1999; Piironen et al., 2002; Könkö et al., 2012; Aro et al., 2013). Nevertheless, even though research in the nutritional and health benefits of oats has advanced significantly, a very different picture is observed on the global scene of oat production. Oats are placed seventh among cereals for cultivated areas, but contribute only 0.86% to the total cereal production worldwide (average for 2009–2013) (FAO, 2013). The dispersion of oat production on a world scale by country is presented in Fig. 1 (FAO, 2015). The world oat cultivated area (average for 2009–2013) is about 9.6 million ha, in comparison to wheat at 220 million ha, and barley at 50 million ha. In most countries, including Europe, the oat cultivated area has continuously declined during the past decades (Fig. 2), partially connected to replacement of horse-drawn implements by modern machinery (historically, oats were the main horse feed). 2 A. Gorash et al. Declining demand for oats significantly reduced the amount and the scope of oat breeding. For example, in 1973 oat breeding was performed by 17 companies in Germany and seven in Austria. These numbers were cut to five in Germany and one in Austria by 2006 (Buerstmayr et al., 2007). Farmers/producers prefer other profitable cereals such as wheat and barley because they produce higher yield and profit compared to oats. Farmers who do choose to produce oats, as a rule select conventional/covered/hulled oats instead of naked oats. On a global scale, about 25%–30% of the average oat grain weight is husk (hull), depending on cultivar, location and year of production (Rhymer, 2002). The thick hulls reduce the total energy and nutritional value of the grain for livestock feeding and add additional cost for transporting, storing or dehulling. The additional yield provided by the hull is valueless, other than to provide protection to the groats during handling. The situation is caused by the absence of an immediately visible market for naked oats, and the same price in the grain market for both conventional and naked oats. Farmers are compelled to choose conventional oats as a more “profitable” crop. Oat breeders follow the preference of growers and buyers, not being willing to divide already small resources, and preferring to concentrate on the improvement of conventional oats. Development of new highly productive naked oat cultivars could eliminate these problems. Reducing hull percentage in oat is an important goal in breeding programmes, since lower hull percentage and higher groat content (a groat is the oat grain minus the hull) improves milling yield and increases the grain value for the millers (Valentine, 1995; Cabral et al., 2000). Nutrition quality Historically, oat production mainly focused on the animal feed market and nowadays, in the world scale, about 75% of oat grain is still used for animal feeding (Webster & Wood, 2011). However, the unique nutritional values and advantages of oats for human consumption as a healthy food were confirmed in recent decades. Recently, the interest in oats for the milling industry and functional food production has increased. The main driving force for the further development of oat breeding, scientific research and increase in oat growing and consumption will depend on developing new cultivars which meet the requirements of millers and consumers. The primary characteristics of oat grain quality are: groat percentage, test weight, protein, fat and 𝛽-glucan level. To a lesser degree, but also important for milling, are easy dehulling, uniform kernels, low groat breakage during dehulling, uniformity of colour and taste (Chu, 2014). Ann Appl Biol (2017) © 2017 Association of Applied Biologists Aspects in oat breeding A. Gorash et al. Figure 1 Oat production quantities (in metric tonnes) by country (average 2009–2013). Figure 2 Changes in world oat cultivated area. Groat percentage and protein content are important both for food and feed. High fat level is more important for feed, providing more metabolisable energy. In contrast, high fat is not desirable for human consumption, because it may cause rancidity and shorten the storage life of oat products. Also, low fat content along with high 𝛽-glucan level is a part of the requirement for health claims on oat products. A high 𝛽-glucan level is more valuable for human consumption and less for animals because higher fibre levels resulted in lower nutritional energy. High Ann Appl Biol (2017) © 2017 Association of Applied Biologists amounts of 𝛽-glucan in oat feeds are inefficiently utilised by poultry, especially by young chicks (Humphreys et al., 1994; Peterson, 2004). Some industrial applications demand minimums for protein and 𝛽-glucan level and maximums for fat concentration, to meet labelling requirements of food end products. That is why a processor may require oat cultivars with specific content of the target compounds. Separate oat nutrients are isolated in industry, such as starch and protein for use in cosmetics, 𝛽-glucan and antioxidants as 3 Aspects in oat breeding complements for human food, and polar lipids extracted for pharmaceutical and food supplements. Therefore, special cultivars with enhanced attributes may be developed for particular applications (Humphreys & Mather, 1996; Doehlert et al., 2001; Peterson, 2004). A. Gorash et al. Table 1 Methods for the measurement of 𝛽-glucan Method References Enzymatic Humphreys et al., 1994 Genç et al., 2001 Tosh et al., 2004 Demirbas, 2005 Havrlentová & Kraic, 2006 McCleary, 2006 Ahmad & Zaffar, 2014 Lambo et al., 2005 Bhatty, 1995 Ahmad et al., 2010 Pérez-Vendrell et al., 1995 Johansson et al., 2004 Demirbas, 2005 Chernyshova, 2006 Virkki et al., 2005 Groat percentage and test weight Groat percentage is under control of one main gene and three modifying genes, so this trait depends mainly on genotype, but some influence of environment is also observed (Marshall & Shaner, 1992; Doehlert et al., 2001) Several researchers have highlighted the high heritability of groat percentage which can be improved through recurrent selection. Test weight (hectolitre weight) is less heritable and highly dependent on the environmental/growing conditions (Doehlert et al., 2001). Protein A number of researchers indicate relatively high heritability of protein content. Normally, however, high protein content is negatively correlated with grain yield (Humphreys & Mather, 1996). The protein level is determined both by genotype and environmental effects. A number of studies show that nitrogen fertilisation increased protein content in oat kernels. Therefore, the protein content can be managed both by proper choice of cultivar and by optimal level of fertilisation (Doehlert et al., 2001; May et al., 2004; Fan et al., 2009). Fat Oats contain higher levels of fat and some genotypes even exceed the fat level of corn (Doehlert et al., 2001; Menon et al., 2016). Oat cultivars with high fat have advantages for animal feeding because of higher metabolisable energy. Studies show high heritability of oil concentration (Branson & Frey, 1989; Schipper & Frey, 1991), and oat lines with 18% fat were developed via recurrent selection programmes (Peterson & Wood, 1997; Frey & Holland, 1999). However, fat content is negatively correlated with 𝛽-glucan and protein content. Accordingly, although the protein concentration increased through applying nitrogen fertilisation, oil decreased (May et al., 2004; Gazal et al., 2014). However, cultivars with high protein and high oil level have been developed (Youngs & Forsberg, 1979). 𝛽-glucan 𝛽-glucan is a polygenic trait controlled mainly by genes with additive effects. Heritability of 𝛽-glucan content 4 Centrifugation-dialysis filtration Extraction using NaOH Alkaline extraction HPLC HPEC-PAD Spectrophotometry in the UV Flow injection analysis (FIA) IR-spectra has ranged from 0.27 to 0.58 (Holthaus et al., 1996; Humphreys & Mather, 1996; Kibite & Edney, 1998). Although 𝛽-glucan content is influenced by environmental factors (nitrogen level and amount of precipitation), the variation due to genotype is generally greater than the environmental effect (Dvončová et al., 2010). 𝛽-glucan content is positively correlated with protein content, but negatively with fat concentration (Kibite & Edney, 1998). The negative correlation with fat content challenges the development of cultivars with high 𝛽-glucan and low-fat content, targeted for human consumption. The selection of genotypes with the desired 𝛽-glucan content can be made in early generations, when adequare seed amounts are available, using laboratory methods of 𝛽-glucan determination. The most common method is an enzymatic method, based on the specific enzymatic degradation of the carbohydrate followed by quantification of the products. Moreover, for rapid measurement of 𝛽-glucan content, several other techniques based on chemical extractions and physical methods have been developed (Table 1). The breeding approaches to improve nutritional quality are mostly based on selection of parents which possess high levels of target traits, followed by hybridisation cycles, pedigree selection and/or recurrent selection. To obtain high genetic variation and valuable transgressive segregants with needed complexes of genes, large segregating populations are required. Laboratory measurements of 𝛽-glucan, protein and fat content may facilitate the phenotypic selection of genotypes with the desired quality characteristics. Molecular genetics is a prospective avenue to facilitate oat breeding for quality traits. For example, markers associated with 𝛽-glucan content have been found (Orr & Molnar, 2008). Ann Appl Biol (2017) © 2017 Association of Applied Biologists A. Gorash et al. Naked oats compared with covered oats are higher in nutrients (protein, fat, oil, antioxidants and others) due to the absence of hulls (Valentine, 1995; Givens et al., 2004). Breeding for naked oats and the development of cultivars targeted for special markets could increase the worldwide value of oats. Naked oats Naked (hulless) oats differ from the covered (husked/ conventional/hulled) types by only a single major gene (with modifying genes). Marshall & Shaner (1992) established that a single, incompletely dominant gene (N-1) interacting with modifying genes (N-2, N-3 and N-4) control the expression of the hulless grain characteristic in oats. Depending on the alleles present at each of the four loci, the different phenotypic expressions of nakedness are observed. A completely naked phenotype is expressed when all alleles at the loci N-1, N-2 and N-3 are homozygous dominant. The presence of homozygous recessive alleles at the loci N-1 will produce the covered phenotype, the recessive alleles of N-2 and N-3 will confer various proportions of ‘mosaic phenotypes’, the mixture of naked and covered kernels (Jenkins & Hanson, 1976). When alleles at the loci N-1 are in a heterozygous condition and the alleles at the N-4 locus are homozygous dominant, a covered phenotype is observed (Kibite, 2002). Modern naked oat cultivars are often not fully naked; hull content may vary from 1% to 15% depending on environment and genotype (Kirkkari et al., 2004; Kirkkari, 2008b). As well as genetic influences, the expression of the nakedness is affected by environmental conditions (Boland & Lawes, 1973; Lawes & Boland, 1974; Marshall & Shaner, 1992). The influence of temperature and humidity on the expression of the nakedness was observed more than 40 years ago. Lawes & Boland (1974) noticed that naked oats grown in greenhouse conditions compared to those grown in the field produced more naked grains. They suggested that the main factor influencing the expression of nakedness is temperature; under 25∘ C the plants of all studied cultivars produced mostly naked grains, whereas at 20–15∘ C expression of nakedness was significantly lower (Lawes & Boland, 1974). Traditionally, it has been argued that naked oat cultivars have a lower yield potential than covered oat cultivars (Peltonen-Sainio, 1997). Covered (husked/conventional) oats usually have two (rarely three or four) fertile florets per spikelet, whereas naked oats are multiflorous (Valentine, 1995). This multiflorous spikelet has led some researchers to speculate the groat yield of naked oats should be higher than that of covered oats because it has potential to produce more grains per spikelet. Others disagree because the groat yield of naked Ann Appl Biol (2017) © 2017 Association of Applied Biologists Aspects in oat breeding oat cultivars in comparison to covered cultivars was significantly lower in the past. Those authors considered that the floral morphology of the naked oats in some way negatively connected with yield potential (Valentine, 1995; Burrows et al., 2001). In recent years, a number of studies have demonstrated that some types of naked oats have already exceeded the groat yield of covered oats. Peltonen-Sainio (1997) studied three naked and two covered lines at varying nitrogen fertiliser and seeding rates in Finland. She established that the naked oat variety Rhiannon produced about 9% higher groat yield than the popular covered Finnish cultivar Veli. The study of naked oats in Nordic European countries during the 1990s and early 2000s indicated that under northern growing conditions, groat yield of naked oats was already similar to that of covered oats; depending on the cultivars compared, it may range from 20% lower to 10% higher (Peltonen-Sainio, 1994, 1997; Kirkkari et al., 2004). A key study of Burrows et al. (2001) compared near-isogenic naked and covered lines and showed there was no significant difference in groat yield between the covered and naked isolines. The study authors concluded that the difference in floral morphology of covered and naked oats had no effect on determining the groat yield potential. Thus, if naked oat cultivars yield fewer groats than covered cultivars, it is not connected with the genes controlling the naked trait and the reduced yield is probably related to other factors (Burrows et al., 2001). Doehlert et al. (2001) reported that groat yield of the naked oat cultivar Paul was higher than groat yields of 11 covered oat cultivars over 12 environments during 3 years in the USA. In the Czech Republic, Moudrý et al. (2004) demonstrated that groat yield was 23% higher in naked than in covered oat varieties. Maunsell et al. (2004) found no significant difference between covered and naked lines for groat production during 2001–2002 in the UK (Maunsell et al., 2004). However, naked oats are relatively new in agriculture, and the few developed cultivars of naked oats indicate that less breeding effort has been undertaken to develop new naked cultivars compared to covered types (Brown & Patterson, 1992). For example, there are 332 cultivars of covered oats and only 35 cultivars of naked oats proposed for production in the European catalogue of crop varieties (European Commission, 2015). Buerstmayr et al. (2007) studied 120 oat genotypes (111 covered and nine naked types) of worldwide origin and demonstrated that the best groat yield of covered lines was significantly higher than the groat yield of naked lines. The top yielding naked cultivar, Abel, produced 15% lower groat yield than the top yielding covered cultivar, Chantilly, in Austrian and German 5 Aspects in oat breeding environments. For this reason, breeders tried to transfer the genetic yield potential of the best covered cultivars to the gene pool of naked oat by crossing with covered types. However, these crosses may also transfer less desirable genes from the covered types. The comparison of groat yield between naked and conventional cultivars will depend on cultivar numbers examined and the oat genetic pool taken for analysis. Naked oat performance may be improved through agronomic management developed specifically for those cultivars. Peltonen-Sainio (1994) reported that naked oat genotypes produce 10% lower groat yield because the naked oats produced fewer panicles per unit area due to lower seedling emergence. The author reported this reduced yield could be improved by increasing seeding rates by 10%. Naked oat cultivars have unique end-use advantages compared to covered cultivars (Burrows et al., 1993); however, numerous limitations, including lower grain yield, have constrained the use of these cultivars. Besides genetic features, naked oat has some restrictions due to its biological properties; absence of the hull makes seeds more susceptible to damage during threshing or storage and can reduce the level of germination (Peltonen-Sainio, 1994; Valentine, 1995; Kirkkari et al., 2001). Agronomic management Oats have been cultivated in marginal cropping areas with low fertility not appropriate for wheat, barley or maize, due to apparent adaptation of oats to a wide range of soil types and ability to perform better on marginal soils than other small-grain cereals. However, oat cannot compete with wheat and barley grain yields under optimal agronomic practices (Stevens et al., 2004; Lorencetti et al., 2006; Buerstmayr et al., 2007; Ren et al., 2007; Vaisi & Golparvar, 2013; Sánchez-Martín et al., 2014). To obtain high yield and quality of naked oat requires some fine tuning of crop management. Among cereal crops, oats are characterised by an extremely soft endosperm texture compared with common wheat, rye and barley (Pedersen et al., 1996; Pogna et al., 2002; Hansen et al., 2004; Iwami et al., 2005; Taddei et al., 2009). A number of authors have considered this trait in oats leads to some negative agronomic traits, especially in naked cultivars. In the absence of hulls, the damage to the embryo during mechanical harvesting and threshing significantly reduces germination percentage as well as grain vitality, healthiness and consequently, decreases the grain yield (Valentine & Hale, 1990; Peltonen-Sainio et al., 2001; Kirkkari et al., 2001). The initial promotion and expansion of naked oats in the UK was constrained because the seed did not meet the minimum official germination standard of 85%. Valentine 6 A. Gorash et al. & Hale (1990) established that hand-threshed grains of naked oat cultivar Rhiannon showed 90% (normal) germination, whereas grains harvested using an experimental plot thresher and a commercial combine harvester gave 83% and 72% germination, respectively (Valentine & Hale, 1990). Subsequently it was proved that the reduced germination of naked oats could be economically compensated for, by increasing the seeding rate. The EC Standing Committee on Seeds accepted a successful submission which allowed naked oat seed to be marketed at 75% germination from 1988 (Valentine, 1995). The caryopsis of naked oats is sensitive to mechanical damage during harvesting, especially at high grain moisture content. To produce naked oat seed with high germination, it is recommended that harvesting be carried out at the lowest grain moisture content possible. However, if this is not feasible, better germination can be attained by reducing the cylinder speed. This reduces mechanical damage to the grain and eliminates the negative influence on grain germination (Kirkkari et al., 2001; Kirkkari, 2008b). Zieliński et al. (2007) investigated the effect of cylinder speed and moisture content on mechanical damage of naked cultivars. The amount of microdamage and damage to the embryo was significantly higher, up to 10% when grain moisture content ranged from 22.9% to 19.3% and with a cylinder speed of 2.4 m·s−1 . Increasing threshing cylinder speed from 1.6 to 2.4 m·s−1 resulted in a 15% increase of the numbers of grains with microdamage and a 40% increase in the area of microdamage. To reduce this microdamage during threshing, the grain moisture content must be between 14% and 16% at harvest (Zieliński et al., 2007). A high germination percentage is essential if oats are to be used as seed material or for particular food processing that requires germination, such as malting. However, low germination does not reduce the value of the crop as feed, or in the food industry where the germination capacity is not important. For seed production, it is also possible to compensate for the reduction in germination by increasing the seeding rate (Valentine & Hale, 1990, Peltonen-Sainio, 1997; Kirkkari et al., 2001). Experiments under Finnish conditions indicate that the seeding rate for naked oats should be increased about 10% more than for covered oats (550 germinating seeds per square metre) due to the lower seedling emergence, and the number of panicles produced per square metre (Peltonen-Sainio & Rajala, 2001; Peltonen-Sainio, 1994, 1997). Increasing the sowing rate from 400 to 790 seeds per square metre caused a significant increase in grain yield, both in naked and covered oats in Poland (Stankowski & Świderska-Ostapiak, 2004). However, in typical situations, a rate of 300 seeds per square metre Ann Appl Biol (2017) © 2017 Association of Applied Biologists Aspects in oat breeding A. Gorash et al. for winter covered types and 400 seeds per square metre for naked oats would be optimum rates in Great Britain (Green, 1999). It has been demonstrated that optimal nitrogen fertilisation significantly increases the protein content, and the proportion of most of the essential amino acids in both covered and naked oat cultivars. However, some differences were observed in the response to nitrogen treatment between them in terms of amino acid composition. According to Givens et al. (2004) glutamic acid, alanine and arginine increased and the proportion of tyrosine, cystine and lysine were slightly reduced in covered oats after nitrogen application, whereas, in the naked cultivars, an increase was observed in the proportion of glutamic acid, phenylalanine and arginine and a slight reduction in the proportion of proline, serine and lysine after nitrogen treatment. However, nitrogen treatment had no significant influence on the proportions of fatty acids in both type of oat cultivars. Nitrogen fertiliser generally increases protein content, but slightly reduces or does not change the oil content (Humphreys et al., 1994; Rhymer, 2002; Givens et al., 2004). The correlation between nitrogen fertilisation and fat content is not as evident as the correlation between nitrogen and protein. Contradictory results for the effects of nitrogen fertilisation on 𝛽-glucan concentration were published. Some authors found significant correlation between nitrogen fertilisation and 𝛽-glucan accumulation (Welch et al., 1991; Brunner & Freed, 1994; Fan et al., 2009; Andersson & Börjesdotter, 2011; Güler, 2011). Other authors reported no significant correlation between application of nitrogen fertiliser and 𝛽-glucan content (Humphreys et al., 1994; Jackson et al., 2010; Weightman et al., 2004; Saastamoinen et al., 2008). The level of 𝛽-glucan can be shifted by other environmental factors. Generally, 𝛽-glucan is higher in warmer and dry climates and lower in cold, wet climates (Brunner & Freed, 1994; Saasatamoinen, 1995; Güler, 2011). The sensitivity of oat cultivars to lodging is an important factor which limits application and effectiveness of nitrogen fertilisation in maximising grain yield. Due to the lodging sensitivity, Ma et al. (2012) did not find positive effects of nitrogen fertilisation on yield grain in both naked and hulled oats. In addition to increasing lodging, increasing the rate of nitrogen fertiliser also decreased test weight and oil concentration. Therefore, depending on the end purpose or use of oat grains, nitrogen fertiliser rates could be changed to optimise the desired traits in the grain (Chalmers et al., 1998; Ma et al., 2012). Generally, oats are less affected by fungus than wheat or barley and requires less fungicide protection (Givens et al., 2004). Possessing resistance to the soil-borne fungus ‘take-all’ (Gaeumannomyces graminis), oats can be an Ann Appl Biol (2017) © 2017 Association of Applied Biologists effective ‘break’ crop for winter wheat in a cereals rotation (Chalmers et al., 1998). However, susceptibility to diseases, especially rusts, which continue to cause severe epidemics in countries where oat production acreage is higher, such as the USA, Canada, China and Brazil, is another important factor decreasing oat productivity (Chong et al., 2011; Li et al., 2015). The most economically profitable and environmentally safe method of protection is plant breeding for disease resistance. The successful solution of oat resistance to diseases requires the development of new methods and complex approaches for oat breeding. Oat breeding for disease resistance The common oat diseases are: rusts (crown rust, stem rust), powdery mildew, smuts (loose smut, covered smut), fusarium head blight and septoria leaf blotch. Crown rust (caused by Puccinia coronata Corda f. species avenae Eriks.) is the most widespread and economically important disease of oat worldwide, occurring in all environments where this cereal is cultivated, with incidence and severity from low to high (Fig. 3; Šebesta et al., 2003; Leonard & Martinelli, 2005; Graichen et al., 2011; Gnanesh et al., 2014; Sikharulidze et al., 2015; G. Montilla-Bascón et al., 2015, personal communication). In Canada, annual yield losses averaged 5.1% during the 5-year period from 2001 to 2005 (Chong et al., 2011), with the highest losses of 11.2% and 8.8% in 2001 and 2005, respectively (McCallum et al., 2007). In the USA, average yield losses for the 10-year period of 1996–2005 were 2.7% up to 20% in individual years and states (Carson, 2009). In the USA, breeding for resistance to crown rust began in 1919 (Simons, 1985), and to date, over 100 resistance genes have been described (Cabral et al., 2014; Gnanesh et al., 2014, 2015). Stem rust (caused by Puccinia graminis Pers. f. sp. avenae Eriks. and Henn.), another important disease for oats, caused severe epidemics in the past in the major oat producing countries: USA, Canada and Australia (Gnanesh et al., 2014). The most recent epidemic of oat stem rust in Canada, observed in the eastern prairie region, caused yield losses of about $14 million (losses about 5%–10%) in 2002 (Fetch, 2005). Similar epidemics occurred in China in 2012–2013, causing yield losses of approximately 10%–15% (Li et al., 2015). Currently, 17 oat stem rust resistance genes (Pg genes) and the Pg-a complex have been described (Gnanesh et al., 2014). Powdery mildew [caused by Blumeria graminis (D.C.) Speer f. sp. avenae Em. Marchal] is the most important foliar disease of oat in the cooler humid regions of Europe, and in some countries of Eastern Europe (Roderick et al., 2000; Okoń, 2015). Clifford (1995) reported annual crop 7 Aspects in oat breeding A. Gorash et al. Figure 3 Spread and economic impact of oat crown rust in the world. losses from 5% to 10% in the UK. Resistance to powdery mildew in oats is governed by major genes that have been characterised as oat mildew resistance (OMR) groups (Jones & Jones, 1979). So far, six OMR groups and seven resistance genes to powdery mildew have been described (Roderick et al., 2000; Yu & Herrmann, 2006; Okoń, 2012, 2015; Hsam et al., 2014), but only three (OMR1, OMR2 and OMR3) have been used commonly in breeding programmes (Okoń, 2012, 2015; Hsam et al., 2014). Fusarium head blight (FHB, Fusarium spp.) has not been reported to have caused large epidemics or yield losses in oats. This may be attributable to the absence of visual symptoms of disease development. Nevertheless, FHB can impact significantly on oat grain quality due to the production of mycotoxins (Tekauz et al., 2004; He et al., 2013; Cabral et al., 2014; Xue et al., 2015). Leaf spot (Pyrenophora avenae), loose smut (Ustilago avenae) and covered smut (Ustilago hordei) are seed-borne diseases which are successfully controlled by fungicidal seed treatments and are not of major importance where these treatments are applied (Clifford, 1995; Šebesta et al., 2001). Coexistence of plants and pathogens in combination with the high evolution potential of pathogens results in the breakdown of plant genetic resistance after fairly short time intervals. The pathogen evolution occurs through sexual recombination and mutations, and the biological 8 ability to spread by air results in continual emergence of new virulence which can be transferred easily within and between continents (Kolmer, 2005; Wellings, 2011). The durability of plant resistance is determined by several factors: genetic complexity [the more genes (transcripts) conferring resistance, the more difficult for the pathogen to evolve virulence]; the more cultivated area with the same genetic base of resistance, the higher probability of virulence emergence; environments and the presence of the alternate host for rusts (favourable environments for pathogen development increase its speed of evolution, the presence of the alternate host supporting sexual recombination). Comprehensive understanding of the underlying mechanisms can assist the efficiency and duration of host genetic resistance. Breeding strategies and concepts for disease resistance In breeding for disease resistance, there have been several breeding strategies proposed: incorporation of major race-specific genes, selection for partial resistance, gene pyramiding and use of multiline cultivars or varietal mixtures (Rubiales & Niks, 2000; Long et al., 2006; Carson, 2009; Cabral, 2009; Jackson et al., 2010; Cabral et al., 2014; Brown, 2015). Most current oat breeding strategies are based on major seedling resistance genes, because race-specific genes are easier to utilise in breeding programmes. However, Ann Appl Biol (2017) © 2017 Association of Applied Biologists A. Gorash et al. large-scale production of oat cultivars with single major gene resistance results in quick emergence of new virulence in the pathogen. Carson (2011) reported oat cultivars with single major gene resistance to crown rust in the USA were generally overcome by the pathogen in 5 years or less after release. Zambonato et al. (2012) underlined that in southern Brazil, resistance to crown rust controlled by race-specific genes is overcome by the pathogen so quickly that it is almost impossible to maintain a sufficient level of resistance by releasing new oat cultivars. Numerous studies have established that partial resistance (non-race-specific or adult plant resistance) does not prevent infection development completely, but reduces the number of pustules per leaf, pustule (uredinial) size, spore production and increases the latency period of pustule development. Partial resistance does not confer a high level of resistance, but due to its slowdown effect on pathogen development, it prevents epidemics of diseases and may provide a long-term solution (Portyanko et al., 2005; Long et al., 2006; Zambonato et al., 2012). Partial resistance against crown rust in oats was identified in several genotypes, for example line MN841801–1 (Portyanko et al., 2005), the oat cultivar URS 21 (Zambonato et al., 2012) and the UFRGS lines (Chaves et al., 2004). Portyanko et al. (2005) investigated molecular markers associated with adult plant resistance (APR) in the line MN841801–1, detecting four major Quantitative trait loci (QTL) and three minor QTL. Acevedo et al. (2010) found additional QTL associated with partial resistance in the same oat line. Lin et al. (2014) detected additional major QTL, which explained up to 76 % of the phenotypic adult plant expression of resistance in MN841801. However, partial resistance is more difficult to apply in plant breeding since, in most cases, it is inherited polygenically and the breeder must select the plants on the basis of quantitative differences in disease reaction. Moreover, the presence of race-specific genes may mask the small effects of genes conferring partial resistance, and under certain environments (and infection pressures) partial resistance can be confused with race-specific resistance (Rubiales & Niks, 2000; Lin et al., 2014). Another concept is to mix different genotypes for sowing in the same plot unit: multiline mixtures, multiline varieties and mixtures of cultivars. Multilines are defined as mixtures of genetically uniform lines (near-isogenic lines) that differ only in resistance to one particular disease (Browning & Frey, 1981). Multiline cultivars are composited of lines (up to 10) that are isogenic for almost all agronomic traits, but only vary genetically in resistance to one specific disease. Cultivar mixtures are blends of agronomically compatible cultivars, but differing in resistance to one disease. Each cultivar of the Ann Appl Biol (2017) © 2017 Association of Applied Biologists Aspects in oat breeding mixture must be phenotypically similar for agronomically important traits including maturity, height, grain quality and type. Thus, the cultivar mixtures are genetically heterogeneous but phenotypically uniform (Lammerts van Bueren et al., 2002). The concept of utilising multi-lines to control diseases was first proposed by Jensen (1952). Some authors (Browning & Frey, 1969; Wolfe, 1985) confirmed the advantages of multi-lines over pure line cultivars in disease control. However, using a mixture of multi-lines and cultivar mixtures can only partially assist in disease control. The mixture should consist of genotypes which all possess effective resistance and should be resistant to all other common diseases, or the multi-line could promote epidemics of other diseases (Van der Plank, 1982). In contrast Browning & Frey (1981) published that populations of Puccinia coronata f. sp. avenae were more virulent on multi-lines than on pure lines. Also, some authors reported that the composition of multi-lines or cultivar mixtures permits selection of complex races that decrease the long-term durability of that resistance (Groth, 1976; Barrett, 1980). Carson (2009), to investigate the interaction between multilines and the population of P. coronata isolates, used multi-line cv. E77. This cultivar was composed of 10 components, all of which contained resistance genes matched to virulence in the pathogen population. The oat plots were planted between parallel hedges of common buckthorn (Rhamnus cathartica L. – an alternate host of P. coronata) to promote sexual recombination in the pathogen. Carson concluded that complex races, “super races”, could emerge rapidly in response to the widespread resistance of an oat multi-line and therefore that resistance cannot be durable. Although multi-lines and/or cultivar mixtures potentially could provide some initial protection against pathogens, due to their observed weak effectiveness and other drawbacks, this approach was not adopted widely (Barrett, 1980; Van der Plank, 1982). Van der Plank (1963), observing the decline of plant resistance and emergence of virulence which caused severe epidemics, postulated that all plant resistance can be classified into one of two categories, horizontal and vertical resistance. Horizontal resistance is usually quantitative (polygenic) and often conditioned by minor genes; vertical resistance is qualitative (oligogenic) and normally conferred by major genes. However, this classification of plant resistance does not correspond completely with practice and new discoveries in science. For example, in wheat, major genes have been identified for resistance against leaf rust: Lr34, Lr46, Lr67 and Lr68, which act as race-non-specific genes (Singh et al., 1998; Hiebert et al., 2010; Da-Silva et al., 2012). Lr34 has been used broadly in wheat breeding programmes around the world since 1966 and has not been overcome by 9 Aspects in oat breeding the pathogen so far (Kolmer et al., 2007; Dakouri et al., 2013). Borojević & Borojević (1971) underlined that dividing resistance into vertical and horizontal categories is not biologically based, rather only a reflection of man’s desire to systematise and explain the phenomena of plant resistance. Nelson (1978) emphasised that the definition of horizontal resistance (minor genes) and vertical resistance (major genes) is not correct, as only resistance genes can be differentiated according to the type of expression and effectiveness. Borojević (1992) emphasised that quantitative resistance is not only controlled by minor genes; major genes also can be involved. Rubiales & Niks (2000) highlighted that we still do not completely understand what mechanisms cause a resistance to be durable, nor how to differentiate durable resistance from non-durable. However, there exist examples in cereals where durable resistance to rusts is controlled by a complex of genes, in others durability is conferred by single genes not resulting in hypersensitivity and acting as race-non-specific. The durability of resistance can be significantly enhanced when combined in one genotype, even race-specific genes with race-non-specific. These authors consider that the combination of genes with different resistance mechanisms can greatly increase the durability of resistance and accordingly that the development of cultivars with single race-specific genes should be avoided (Rubiales & Niks, 2000). Prospects of disease resistance breeding in oats The efficacy of oat breeding for disease resistance depends on understanding the mechanisms of plant–pathogen interactions and proper breeding methodology for disease resistance. Better understanding of plant–pathogen interaction systems and mechanisms of plant resistance can be attained through research at cellular and molecular levels. Sanchez-Martin et al. (2011), through detailed histological study, found two oat cultivars and nine landraces with a high level of APR to powdery mildew. The results of this study showed that cell-wall-associated penetration resistance was one of the primary components of adult plant resistance. Moreover, pathogen colonies developed in the adult plant produced a lower number of secondary hyphae compared with the colonies infecting the first/seedling leaves. Sanchez-Martin et al. (2011) suggested that if the penetration resistance was combined with genes responsible for limiting colony growth, it would be possible to develop cultivars with a high level of durable resistance. Coram et al. (2008a,b) and Chen et al. (2013) used a transcriptomics approach to detect the differences in molecular mechanisms of durable and non-durable resistance to stripe rust in wheat. They chose 10 A. Gorash et al. an all-stage resistance gene Yr39 and race-specific gene Yr5. Their results indicated that Yr39 produced 113 transcripts, while Yr5 produced 75. The transcripts involved in high-temperature adult-plant resistance were shown to be induced more slowly than transcripts involved in all-stage resistance. Pioneering work in molecular mechanisms of host–pathogen interaction indicates that applying transcriptome analysis will allow, not only a deeper understanding of the molecular mechanisms, but also enable selection of genes for producing durable resistance. The analysis may have revealed which genes are more likely to be durable and which are not (Coram et al., 2008a,b; Chen et al., 2013). Oat breeding strategies for disease resistance are mostly based on screening for resistant genotypes and involving them in hybridisation programmes. The successful selection of resistant genotypes depends on proper infection pressure. The absence of favourable conditions for disease development makes the proper visual selection of resistant genotypes not possible. The evaluation of plant resistance can be done after artificial disease inoculation in environments where natural growth of disease is not enough for estimation. Interspecific crosses will continue to be an important source of new effective genes of resistance in the future, together with partial resistance through the accumulation of minor race-non-specific genes by inter-crossing oat lines or cultivars with partial resistance. Durable resistance in most cases is based on a complex of minor race-non-specific genes, or on a combination of minor genes with major race-specific genes. It can be impossible to select plants by phenotype if they contain major genes plus minor race-non-specific genes or to separate genotypes with one major gene from genotypes with two, three and more major genes (pyramided genes). Therefore, marker-assisted selection (MAS) simplifies the pyramiding of genes by enabling detection of any number of resistance genes in one genotype. Health claims and oat market The effective nutrition marketing of oat products started in 1980 by the Quaker Oats Company. However, the advertising approaches of the Quaker Company, without scientific evidence for the beneficial properties of oat for human health, were unable to effectively promote the production and consumption of oat products (Chu, 2014). In 1995 the Quaker Oats Company filed a petition for the first health claim, summarising 37 studies, as evidence that consumption of oat products reduces the risk of coronary heart disease. In response to that petition, the U.S. Food and Drug Administration (FDA) confirmed the claim (U.S. FDA, 1997). Since then, oats have been publicly recognised as a health food with unique benefits Ann Appl Biol (2017) © 2017 Association of Applied Biologists A. Gorash et al. and properties. This created a new “brand” around oats and a market advantage for oat production for human consumption (Chu, 2014). Consequently, in 2004 the United Kingdom Joint Health Claims Initiative (JHCI) recognised the cholesterol-lowering health claim for oat 𝛽-glucan (JHCI, 2004). In 2007, Health Canada received a petition from industry for a health claim on disease risk reduction for oat products (Nwachukwu et al., 2015). Health Canada confirmed that consumption of oat 𝛽-glucan reduces blood cholesterol (Health Canada, 2010; Menon et al., 2016). The Union European Food Safety Authority (EFSA) Panel on Dietetic Products, Nutrition and Allergies (NDA), in response to a petition filed by Crea-Nutrition AG, endorsed that the consumption of oat 𝛽-glucan decreases the concentration of LDL cholesterol in blood. The panel highlighted that in order to fit the claim, oat products containing no less than 3 g of oat 𝛽-glucan should be consumed per day (EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA), 2010, 2011). The scientifically supported health approval of oat products in the USA, Canada and the European Union has resulted in an improved market for oats. The crop formerly considered a livestock feed obtained worldwide approval as a healthful food for humans. Therefore, the successful development and introduction of naked oats depends on availability of markets where its quality advantages are recognised (Valentine, 1995; Chu, 2014). Kirkkari (2008a) analysed the economics for production of naked and covered oats, considering cultivation, dehulling and grain prices. This analysis showed the main economic differences are connected with market price and yield levels, and profitability considerably dependent on price. When naked oats are sold at a specific price, it is more profitable than covered oats at all yield levels. When naked oats are sold as a feed for livestock it is more profitable only at the highest yield level. Dehulled oats do not attain the same economic profit as naked oats at any yield level, due the considerable cost of dehulling and disposing of the hull waste. In the UK, a “new culture” was initiated in 1983 when feed manufacturers, animal nutritionists and oat millers were invited to evaluate naked oats. The first research and introduction of naked oat was focused on the animal feed market. It was determined that the high oil content and low fibre level provided a higher metabolisable energy for pigs, poultry and non-ruminants than wheat or barley (Valentine, 1995). Subsequent trials in livestock largely confirmed the high nutritional value of naked oats through increasing live weight gains and feed conversion rates (Valentine, 1995). In Canada, Morris & Burrows (1986) showed that the substitution of maize with naked oats high in protein allowed the total replacement Ann Appl Biol (2017) © 2017 Association of Applied Biologists Aspects in oat breeding of soymeal in a finisher pig ration. Naked oats produced a 50% faster growth rate than wheat or barley. Naked oats also demonstrated good results in poultry trials (Cave & Burrows, 1984; Hulan & Proudfoot, 1986, 1987; Valentine, 1989; Burrows et al., 1992). Doyle & Valentine (1988) calculated the individual price in relation to the energy, protein content and amino acid requirements, to formulate the least average price for naked oats, wheat and barley in the diet of dairy cows, beef cattle and pigs. They concluded the price for naked oats for feeding pigs should be 114% higher than wheat and 132% higher than barley, for feeding dairy cattle – 113% and 114%, respectively, for feeding beef cattle – 113% and 120%, respectively. They concluded that a switch from barley to naked oats in pig diets would result in a significant saving for pork producers in the United Kingdom (Doyle & Valentine, 1988). From 1989 commercial companies in the United Kingdom have contracted farmers to grow naked oats which they purchase back at a premium price (£139 t−1 ), £35 t−1 above barley in 1991 (Valentine, 1995). Now in the UK, farmers can contract with companies via the internet for premium prices from £30 to £50 over the base price (or over the feed wheat price) (http://www.nidera-uk.com/ products/grain/oats/; http://www.farming4profit.co.uk/ contract/naked-oats/; http://copeseeds.co.uk/products/ conventional-seed/conventional-oats/organic-nakedoats/). However, achieving a premium price for naked oat worldwide is still unattainable. In a global grain market, oat prices for four major oat producing countries from 1991 to 2014 increased on average by 307%. The average price within those areas was 187 US$ t−1 in 2014 (Fig. 4). In comparison, the price of the world cereal leader (wheat) for the same period of time increased on average 258%, with the average price of 251 US$ t−1 in 2014 (Fig. 5) (FAO, 2015). Molecular genetics and biotechnology methods Molecular genetics research of oats has a huge gap compared with other cereal crops due to the size and complexity of its genome and by the lack of DNA sequence information. The limited financing of oat research has resulted in a deficit of a complete set of either nullisomic or nullitetrasomic lines (Gazal et al., 2014). However, since the first linkage-based QTL map was developed by O’Donoughue et al. (1995), there have been continued efforts to increase the density of the map with various kinds and numbers of markers in oats. Several mapping populations were developed using amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) markers (Jin et al., 2000; Groh et al., 2001; Wight et al., 11 Aspects in oat breeding A. Gorash et al. Figure 4 Producer oat prices of top four producing countries (1991–2014, US$ t−1 ). Figure 5 Producer wheat prices of top four producing countries (1991–2014, US% t−1 ). 2003), or in combination with RAPDs, ISSRs, SCARs (De Koeyer et al., 2004; Barbosa et al., 2006). The first doubled haploid linkage map for cultivated oats was created in 2008 (Tanhuanpä et al., 2008). The map is composed of 28 linkage groups containing 625 DNA markers including AFLPs, ISSRs, SSR, RAPDs, IRAPs and SNPs. Oliver et al. (2013) developed and published the first physically anchored hexaploid oat linkage map. The consensus map included 985 SNPs and 68 previously published 12 markers, resolving 21 linkage groups with a total map distance of 1838.8 cM. Tinker et al. (2014) developed a SNP genotyping array for hexaploid oat including 4975 SNPs. A genetic linkage map of hexaploid naked oats consisting of 22 linkage groups covering 2070.50 cM was constructed by Song et al. (2015) including 208 SSR markers. Alternative approaches for QTL detection are genomewide association studies (GWAS). GWAS is the method Ann Appl Biol (2017) © 2017 Association of Applied Biologists Aspects in oat breeding A. Gorash et al. of choice for accurate identification of genomic regions that are in linkage disequilibrium (LD) with QTL influencing traits of interest in natural populations or breeding germplasm (Price et al., 2010). Newell et al. (2011) indicated that GWAS in oats can be a successful option for QTL detection using diversity array technology (DArT) markers. In oats, only a few association analysis studies have been reported. Studies were published focused mainly on grain quality traits such as 𝛽-glucan concentration (Newell et al., 2011; Asoro et al., 2013), disease resistance (Gnanesh et al., 2015; Montilla-Bascón et al., 2015), spikelet number (Pellizzaro et al., 2016) and heading date (Klos et al., 2016). A genotyping platform developed for oats by Tinker et al. (2014) was successfully applied to identify molecular markers in two hexaploid naked oat populations (Pellizzaro et al., 2016). The first marker, GMI_ES17_c5923_221, was linked to a gene controlling the trait multiflorous spikelet. Klos et al. (2016) published results of The Collaborative Oat Research Enterprise (CORE), a global partnership spanning more than 30 sites and collaborating institutions. This wide range study evaluated genetic diversity, characterised population structure, examined the extent of pair-wise LD, and presented GWAS results for heading date (Klos et al., 2016). Four linkage groups were found associated with heading date across the location/years by using two marker platforms developed by Huang et al. (2014) and Tinker et al. (2014) (Klos et al., 2016). Massman et al. (2013) showed that genome sequencing (GS) can be more efficient than MAS for improving complex traits. Asoro et al. (2013) compared efficiency of genomic, marker-assisted and best linear unbiased prediction (BLUP) for selection for 𝛽-glucan concentration. These authors concluded the genomic method is superior for complex polygenic trait selection. However, although the genomic method provides a rapid increase in 𝛽-glucan concentration, it also leads to faster loss of genetic diversity. Therefore, Asoro et al. (2013) concluded that applying GS in large-scale breeding programmes should be combined with other methods to preserve genetic variation. Genotyping-by-sequencing (GBS) is one of the newest, low cost and powerful genetics approaches which can be applied both for general breeding purposes and in genomic studies. This method is attractive because it provides quick genome representation by digesting the genome into fragments that can be parallel sequenced by other high-throughput genotyping techniques (Elshire et al., 2011; Huang et al., 2014). During the last decade plant mutagenesis was rebirthed with the development of TILLING (Targeting Induced Local Lesions in Genomes) technology (Sikora et al., 2011). TILLING is an advanced mutation breeding Ann Appl Biol (2017) © 2017 Association of Applied Biologists method and is considered a non-genetically modified technology. In TILLING, traditional mutagenesis is combined with high-resolution mutation screening. This strategy expands the variation of traits in populations and allows detection of point mutations in individual plants with improved or novel valuable characteristics (Parry et al., 2009). Chawade et al. (2010) developed a TILLING population for spring hexaploid oats, consisting of 2550 different mutagenised seed lines. These researchers were able to identify several different mutations, including AsPAL1 and AsCslF6, which are key genes in the lignin and 𝛽-glucan biosynthetic pathways. The results demonstrated the potential of the oat TILLING population as a method for improvement or development of new specific, valuable oat characteristics. Vivekanand et al. (2014) identified significant qualitative differences in seed lignin levels between the oat TILLING population created by Chawade et al. (2010) and the cultivar Belinda, from which the TILLING population was developed. Preliminary experiments with in vitro digestion showed that some of the mutated seeds were significantly more digestible for ruminant animals than seeds of the initial cultivar Belinda. Although molecular genetics research in oats lags behind compared to other cash crops, it was proved that application of molecular breeding approaches such as MAS, mutagenesis (TILLING) and GBS, in addition to the conventional breeding methods, can facilitate the development of new competitive cultivars and provide a great leap forward (Pérez-de-Castro et al., 2012; Newell & Jannink, 2014). Future perspectives According to reports from the United States Department of Agriculture (USDA), from 1960 to 2005 the yield increase in oats was the smallest (39%) among all of the main cereals. The yield increase for wheat over the same time period was 147%, and 143% for corn (Menon et al., 2016). Theoretically the unrealised genetic potential for oat improvement may be bigger than in other cereals. Smaller breeding efforts have been invested in naked oats, which may actually possess a higher proportion of valuable nutrients and be more economically profitable. The main task in oat breeding should be focused both on yield increase and improving the nutritional quality. Moreover, correction of yield capacity should be done through increasing groat yield. For oat to become an ingredient in functional food, new cultivars should be developed with increased contents of 𝛽-glucan. Further oat improvement for polygenic traits, such as durable resistance to diseases, 𝛽-glucan, nutritional 13 Aspects in oat breeding content, and yield, can be facilitated considerably by using molecular breeding approaches such as MAS, genome-wide association studies (GWA) and mutagenesis (TILLING). The decline of oat production in global terms and the challenges associated ensure that successful development in future requires more genetics, agronomy, technological, and plant breeding research plus political efforts in order to develop and promote the cultivation of high yielding naked oat. The introduction of new highly productive naked cultivars will promote the production and increase the economic efficiency of growing oats. Conclusions The present review has described the current achievements and challenges in oat breeding. The importance of oats for human health improvement and prevention against diseases has been highlighted. Also, due to the superior amino acid profile and high fat content, oats have some advantages over wheat and barley for livestock feeding. However, less research investment and fewer commercial breeding efforts have resulted in the lower competitiveness of oats compared with other cereals, such as corn, wheat and barley. Oats are a multipurpose crop, with different quality requirements for food and feed purposes, and development of target markets for special oat nutrients will require specific varieties to be developed. With the difficulties of combining all required traits at specific levels in one genotype, and different nutritional requirements for oat cultivars, it may be reasonable to diverge breeding efforts for developing cultivars with particular traits. Developing high-yielding cultivars with high groat percentage is the main priority for oat breeding. However, oat cultivars with higher 𝛽-glucan level and lower fat are more desirable for human food markets, whereas cultivars with high protein and fat, and less fibre possess higher nutritional energy and may be developed for the animal feed market. The grains of naked cultivars compared with covered are considerably higher in metabolisable energy, fat, protein and 𝛽-glucan content. Grain oat quality, besides genetic factors, depends on agronomic management. Nitrogen fertilisation can significantly maximise grain yield and increases protein concentration, but decreases other grain quality parameters such as hectolitre weight and fat level. In recent years, oat genetics and genomic research has advanced rapidly, but to keep oats competitive with other cereal crops, further progress with modern techniques in molecular genetics is needed. 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