The Role of Plant Genetic Resources and Grain Variety Mixtures in Building Sustainable Agriculture in the Context of Climate Change

Abstract

In an era of global warming, sustainable agriculture, which emphasises the conservation of biodiversity and the rational use of natural resources, is growing in importance. One of the key elements is to increase the genetic diversity of crops through the use of crop wild relatives (CWRs) and local varieties, which provide a source of genes for resistance to biotic and abiotic stresses. Modern agricultural systems are characterised by low biodiversity, which increases the susceptibility of plants to diseases and pests. Growing mixtures of varieties, both intra- and interspecific, is a practical strategy to increase plant resistance, stabilise yields and reduce pathogen pressure. This manuscript has a review character and synthesises the current literature on the use of CWRs, local varieties, and variety mixtures in sustainable agriculture. The main research question of the study is to what extent plant genetic resources, including CWRs and local varieties, as well as the cultivation of variety mixtures, can promote plant resistance, stabilise yields and contribute to sustainable agriculture under climate change. The objectives of the study are to assess the role of genetic resources and variety mixtures in maintaining biodiversity and yield stability, and to analyse the potential of CWRs and local varieties in enhancing plant resistance. Additionally, the study investigates the impact of variety mixtures in reducing disease and pest development, and identifies barriers to the use of genetic resources in breeding along with strategies to overcome them. The study takes an interdisciplinary approach including literature and gene bank data analysis (in situ and ex situ), field trials of cultivar mixtures under different environmental conditions, genetic and molecular analysis of CWRs, the use of modern genome editing techniques (CRISPR/Cas9) and assessment of ecological mechanisms of mixed crops such as barrier effect, and induced resistance and complementarity. In addition, the study considers collaboration with participatory and evolutionary breeding programmes (EPBs/PPBs) to adapt local varieties to specific environmental conditions. The results of the study indicate that the integration of plant genetic resources with the practice of cultivating variety mixtures creates a synergistic model that enhances plant resilience and stabilises yields. This approach also promotes agroecosystem conservation, contributing to sustainable agriculture under climate change.

1. Introduction

In the era of global warming, the rational use of sustainable agricultural practices is gaining popularity. According to the 1987 definition by the Food and Agriculture Organization of the United Nations (FAO), sustainable agriculture “involves the use and conservation of natural resources and the orientation of technology and institutions in such a way as to meet the needs of present and future generations” [1,2]. One of the most important aspects of sustainable agriculture is the protection of biodiversity, which is the foundation of agricultural ecosystems [3]. Current agricultural systems are often characterized by low levels of biodiversity, making them more susceptible to disease and pest pressure [4]. The greatest threats to biodiversity include the intensification and expansion of agriculture, excessive use of fertilizers and pesticides, and the degradation of natural habitats, leading to species diversity being, on average, 40% lower than in the original vegetation [3].

Integrated Pest Management (IPM) guidelines and upcoming European Green Deal regulations emphasize biodiversity’s importance. Growing cereals in mixed crops, both inter-species and inter-varietal, represents a practical and cost-effective strategy. The key is the selection of genetically diverse components that combine resistance and susceptibility to main diseases, ensuring a balance between productivity and resilience [5].

Global warming, gene pool depletion, and crop production intensification are significant challenges for modern agriculture [6,7,8]. These elements are closely intertwined and require a strategic, integrated approach, particularly in plant resistance breeding. Research on Climate-Smart Agriculture demonstrates that addressing climate change requires integrating agronomic approaches, such as conservation agriculture and improved varieties. It also involves ecological strategies, including resource conservation and emission reduction, and evolutionary approaches like genomics and variety adaptation [6,7,8]. Studies show that combining these strategies enhances both crop resilience and yield stability [9]. The ecological approach emphasizes the preservation of agrobiodiversity and plant–plant interactions, considering genotypes, environment, and their interactions in crop stability and ecosystem services [10,11,12,13]. Agronomic practices, combined with participatory science, enable testing of variety mixtures and the development of locally adapted cultivars. The evolutionary approach identifies adaptive variants and traits enhancing resilience through experimental evolution, genetic mapping, and molecular phenotyping [5]. The synergy of these perspectives fosters innovative breeding tools, yield stabilization, and improved resistance of cropping systems to biotic and abiotic stresses.

Plant genetic resources (PGRs), defined as reproductive material currently in cultivation, including primitive, ancient, and local varieties, as well as elite breeding lines, are collected in gene banks worldwide [14]. These genetic resources provide a unique and diverse gene pool, offering intraspecific variability essential for breeding crops adapted to changing environmental conditions [15,16]. Climate change and selective breeding focused on yield have narrowed the gene pool in crop plants, leading to a gradual and irreversible loss of intra- and inter-species diversity and increased differentiation between populations due to fragmentation and limited gene flow [17].

Increasing crop biodiversity is a current direction in sustainable agriculture. Crop diversity enhances productivity through beneficial interactions between plants and soil microorganisms [18,19,20]. Maintaining biodiversity also influences crop susceptibility and tolerance to pests and diseases. Studies on resistance to fungal diseases and pests in intraspecific mixtures of rice, maize, and soybeans confirm these benefits [20,21,22]. Rising temperatures and rainfall variability affect fungal diseases, cereal parasites, and viruses. For instance, maize streak virus can cause crop losses of 30–100%, while warmer, wetter conditions favor the spread of bacterial diseases in rice and soil nematodes, reducing maize yields by over 25% [23]. Climate warming increases pathogen mobility, reducing crop quantity and quality, and threatening food security.

Currently, a decline in the diversity of cultivated wheat is observed in most European countries, with the exception of Finland, Belgium, and France, where biodiversity is increasing [17]. Slovakia has also been identified as an effective source of biodiversity [17]. Interspecific and intraspecific mixtures can support sustainable agriculture by stabilizing yields and reducing pathogen and pest pressure [5].

The main objective of this study is to assess the role of plant genetic resources and cereal variety mixtures in maintaining biodiversity and yield stability under climate change, and to evaluate their contribution to sustainable agricultural systems. The analysis focuses on examining the potential of crop wild relatives (CWRs) and local varieties to increase crop resistance to biotic and abiotic stresses, as well as assessing the impact of using mixtures of cereal varieties and species on stabilizing yields and limiting the development of diseases and pests. Biological, genetic, and technological barriers limiting the use of plant genetic resources in breeding and strategies to overcome them are also considered. Understanding the available genetic sources of resistance in wheat and barley is essential for developing effective breeding strategies and integrated plant protection, which constitutes a central element of this study.

We hypothesize that including genetic resources, crop wild relatives and local varieties, together with the cultivation of cereal variety mixtures, enhances biodiversity, crop resilience, and adaptation to biotic and abiotic stresses, thereby supporting sustainable agriculture in a global warming context. The manuscript has a review character and synthesizes the current literature on the role of CWRs, local varieties, and variety mixtures in sustainable agriculture. This study emphasizes that understanding the genetic sources of resistance in wheat and barley is key to developing strategies that combine breeding and integrated plant protection.

This study aims to answer the following questions: to what extent can genetic resources be a source of new adaptive traits in plant breeding, what ecological mechanisms—such as induced resistance, barrier effect, or complementarity—are responsible for the benefits observed in mixed crops, and how the integration of genetic resources and mixing practices can support the implementation of sustainable agricultural systems in Europe.

2. Materials and Methods

2.1. Nature and Purpose of the Work

This work is a systematic review and a synthetic study of the current state of knowledge on the role of crop genetic resources, their wild relatives (CWRs), local varieties, and variety mixtures in shaping sustainable agriculture in the context of climate change.

The aim of the study was to:

• present the importance of genetic diversity for plant resistance and crop stability,
• discuss strategies for the conservation and use of genetic resources (in situ and ex situ),
• analyze the application of modern genome editing techniques (CRISPR/Cas9, base editing, prime editing),
• to identify synergies between genetic resources, variety mixtures, and participatory breeding (EPB/PPB).

2.2. Data Sources

Scientific publications, project reports, gene bank data, and documents from international organizations were analyzed. The analysis included original articles, review articles, and reports describing the use of CWRs, local varieties, and variety mixtures in sustainable crop production.

2.3. Review Procedure

The review process consisted of four stages:

• Identification of sources—searching for publications using specific keywords: crop wild relatives, plant genetic resources, variety mixtures, biodiversity, wheat, barley, sustainable agriculture, CRISPR, in situ conservation, ex situ conservation.
• Publication selection—elimination of duplicates and materials of low scientific quality.
• Qualitative analysis—evaluation of content in relation to the research objectives and thematic areas.
• Comparative synthesis—compilation of agronomic, genetic, and ecological research results in the context of sustainable agriculture and adaptation to climate change.

2.4. Analytical Framework

The analysis was based on three complementary approaches:

• agronomic—assessment of the effectiveness of inter- and intraspecific mixtures in reducing pathogen pressure and stabilizing yields,
• ecological—analysis of mechanisms such as the barrier effect, induced resistance, and genotype complementarity,
• evolutionary-genetic—identification of adaptive alleles and genetic mechanisms in CWRs and local varieties associated with tolerance to biotic and abiotic stresses.

2.5. Genome Editing Techniques

Particular attention was paid to modern genome editing techniques such as CRISPR/Cas9, base editing, and prime editing, which enable the rapid and precise introduction of resistance genes and quality traits into crop varieties. Examples of their applications in wheat, barley, rice, and tomatoes were analyzed, as well as technological limitations related to transformability and genome complexity.

2.6. Example of Practical Application

An example of the practical implementation of the concept of genetic diversity and participatory breeding is the LIVESEED project, which is being carried out in European countries. The project promotes organic breeding, the preservation of local varieties, and the development of so-called organic heterogeneous material, which is an example of the integration of on-farm gene resource conservation with participatory and evolutionary breeding.

2.7. Limitations of the Study

The study is based solely on secondary sources, which entails certain limitations. The most important of these are incomplete genomic data for some CWR species, varying quality and comparability of studies, and a lack of field data from Central and Eastern Europe. Despite these limitations, the study provides a comprehensive synthesis of the current state of knowledge and identifies key research gaps and directions for further analysis on the use of genetic resources in sustainable agriculture.

3. Genetic Diversity for Sustainable Agriculture

3.1. The Importance and Applications of Crop Wild Relatives in Sustainable Agriculture

Crop wild relatives (CWRs) are a crucial source of genetic biodiversity, representing a unique gene pool present in the genomes of wild species, including both the ancestors of cultivated plants and closely related species [24]. CWRs have been used in breeding programs for over a century, and with the rapid advances in molecular biology and gene-editing techniques, transferring beneficial genes is now technically feasible. Their applications include increasing plant resistance to diseases and pests (biotic stress), improving tolerance to environmental stress (abiotic stress), and enhancing the nutritional value of crops. The economic significance of CWRs is substantial—already in the 1980s, their contribution to improving crop yields and quality in the US was estimated at over $340 million annually [24], while a 2013 analysis of 32 crops indicated annual benefits of approximately USD 68 billion, with potential future benefits of USD 196 billion [14,25]. The contribution of CWRs to plant breeding has generated substantial economic benefits for agriculture worldwide, estimated at around $186.3 billion in 2020 [26]. Over the last 80 years, it has also been found that yields have increased by around 30%, equating to USD 100 billion, as a result of CWRs being used in plant cultivation [27]. For instance, the wild variety of tomato enriched the gene pool with genes that increased solid content by 2.4%, generating an annual profit of USD 250 million for the global tomato industry. Similarly, three wild varieties of peanut whose genes increased resistance to a certain type of nematode resulted in savings of around $100 million per year worldwide [28].

The effects of climate change pose serious challenges to agricultural production and food systems. Greater crop diversification and the availability of more climate-resilient varieties are essential. CWRs represent a broad and diverse source of genetic variation, which can be harnessed in resistance breeding. It is uncertain how long currently cultivated varieties will remain sufficiently resistant to diseases and pests under changing climatic conditions. CWRs possess desirable traits that can be transferred to cultivated plants, increasing their resistance to biotic stresses, tolerance to drought, and resilience to other adverse environmental conditions.

Rising temperatures, biotic and abiotic stresses—including salinity and drought—and the emergence of new pest and disease strains threaten crop growth and yields. Additionally, the domestication process has reduced the diversity of modern crops, both locally and at the genomic level [29]. For example, rice cultivation has lost over half of its genetic variability [30], and substantial reductions have also been observed in maize [31] and soybean [32] compared to their wild ancestors. To address these challenges, it is necessary to develop new crop varieties using CWRs that are resistant to both abiotic and biotic stresses, including drought and high temperatures, with improved pest and disease resistance, and optimized resource use [33].

3.2. Gene Pools and Challenges in Using Crop Wild Relatives (CWRs)

In resistance breeding, wild relatives of cultivated plants are increasingly utilized as sources of genetic diversity, resistance to biotic stress, and tolerance to abiotic stress. Despite growing interest in CWRs, their practical use in breeding programs faces several significant barriers and challenges [8,28].

The most serious difficulties undoubtedly include biological and genetic barriers. Difficulties in crossbreeding result primarily from ploidy. Cross-incompatibility significantly limits the possibility of desirable selection for a specific trait [28].

Plant genetic resources within a given species are divided into gene pools based on genetic relatedness [28,33]. The literature distinguishes four main types of gene pools forming the basis of genetic diversity in crops and their wild relatives [8,34,35,36].

The primary gene pool includes cultivated species, their varieties, and wild species capable of producing fully fertile hybrids with domesticated forms. This pool contains many useful alleles often lost in breeding. Examples: local and old wheat varieties, wild ancestors like Triticum turgidum, T. tauschii, diploid barley and local varieties [37].

The secondary gene pool includes species closely related to crops with crossbreeding barriers. Gene transfer here is difficult, often with low seed viability or recombination disorders. Examples: polyploid T. timopheevii, Hordeum bulbosum, Secale silvestre [38,39]. The tertiary gene pool consists of distantly related species without shared genomes, preventing homologous crossing. Gene transfer requires chromosome or genetic engineering. Examples: Hordeum bogdanii, species of Triticum and Aegilops used in wheat breeding [8,40]. The quaternary gene pool consists of synthetic forms not found in nature, created through genetic transformation [8,36,41].

Another challenge in utilizing CWRs is the so-called linkage drag effect. When beneficial traits from wild species are introduced into elite cultivars, undesirable traits—affecting yield or disease resistance, among others—can also be transferred. This occurs because undesirable genes located near beneficial genes are co-introduced, and their removal is difficult [28,42]. Wild relatives of cultivated plants (CWRs) have enormous potential for breeding and sustainable agriculture, but their use faces numerous barriers. Worldwide, approximately 7.4 million individual CWRs are stored in around 1750 gene banks (ICARDA 132,793, 2008 data). Genomic data is lacking for a significant proportion of the available accessions. This hinders their molecular characterization and use in marker-assisted breeding. In addition, imprecise taxonomic classification and a lack of knowledge about gene-trait relationships and allele expression in different genetic gene pool make it difficult to assess their usefulness and compatibility [28].

The use of CWRs in breeding practice is also hampered by logistical and technological barriers. Sampling from natural, remote sites is difficult. In addition, the regeneration of CWRs after transformation is very often limited. This limits the possibilities for their rapid domestication.

3.3. Conservation and Use of Crop Wild Relatives: In Situ and Ex Situ Strategies

Plant genetic resources are vital in enhancing plant resilience and ensuring food security. As the world’s population grows, so does the demand for plant genetic diversity. Therefore, the global conservation of these resources is becoming a key priority. Two primary methods of preserving these resources are in situ and ex situ [43].

In situ conservation involves protecting genetic resources in their natural habitats, enabling plants to develop and adapt to changing environmental conditions. One example is the preservation of traditional plant varieties grown directly in fields, which allows farmers to select the most valuable plants and promotes natural evolution. Another example is protecting wild plant species in nature reserves or forests [44].

Ex situ conservation involves storing genetic resources outside their natural environment. The most common form is seed banks, which store seeds long-term at low temperatures, typically between −18 °C and −20 °C, preserving their germination capacity for many years [45]. Gene banks are a key form of ex situ conservation, crucial for preserving plant genetic diversity, particularly seeds. There are approximately 1750 gene banks worldwide, storing over 6 million specimens. In Europe, 461 gene banks hold nearly 2.1 million accessions (Figure 1). The largest European collections are in the United Kingdom (848,922), Russia (200,717), and Germany (185,014) [46]. Most stored specimens are cereals (45%), followed by legumes (15%), fruits and fodder plants (6–9% each), and root and tuber vegetables, oil, and fiber plants (2–3% each). Seeds account for about 90% of all conserved resources, with less than 10% stored in vivo (field gene banks) and around 1% stored in vitro (tissue cultures and cryopreservation). Therefore, research on seed longevity and storage methods is crucial to improve conservation efficiency [47].

Another ex situ conservation method is plant tissue culture, enabling mass propagation and storage of vegetative material under controlled conditions. Cryopreservation involves storing plant tissues at extremely low temperatures, typically in liquid nitrogen at −196 °C, halting metabolic processes entirely and ensuring long-term protection of genetic material [48]. DNA banks store genetic material in isolated DNA, which is essential for species that are difficult to preserve using traditional methods or threatened with extinction [49]. Another approach is collecting digital DNA sequence information (DSI), which involves digitizing molecular data for specific species [43].

There is an urgent need to identify and protect wild crop relatives threatened by climate change. While increased habitat protection is important for most species, those predicted to experience severe range reductions should be prioritized for collection and inclusion in gene banks (ex situ conservation). In situ conservation is also essential to maintain a greater margin of genetic diversity, ensuring that CWR habitats are protected and wild species can continue evolving naturally [24,50].

Wild species and local populations maintain biodiversity and provide resilience to abiotic and biotic stresses [51]. Gene banks, offering ex situ and in situ conservation, play a crucial role in preserving the diversity found in crop species [52]. Moreover, wild plant species and local populations represent the genetic richness of natural plant populations, enabling adaptation to changing environmental conditions and contributing to ecosystem biodiversity and integrity.

The importance of wheat as a major global crop is reflected in the number of wheat specimens stored in gene banks. The largest collections contain 856,000 wheat specimens, followed by rice (774,000) and barley (467,000). In Gatersleben, extensive screening for fungal disease resistance and plant responses to abiotic stresses has been conducted. Phytopathological tests involved 10,348 plants from 21 Triticum species and 489 plants from 20 Aegilops species. Results showed high variability in disease resistance and susceptibility [53].

Wild-growing crop species face genetic erosion and extinction. It is estimated that 15–37% of wild plant species are threatened with extinction [54]. Jarvis et al. [24] estimate that 16–22% of wild relatives of cultivated plants may be threatened. Studies using species distribution models indicate range losses for wild crop relatives, with particular emphasis on wild potato (Solanum) species. Range reductions are projected at 38–69%, with 108 Solanum species predicted to become extinct [24]. These findings align with Huang et al. [42], who report that 16–35% of species in various US regions are threatened, with 7% critically endangered and 50% endangered in their natural habitats. Globally, about one-third of priority CWRs are unprotected, another third are poorly protected, and 95% require additional data collection [42].

3.4. Crop Wild Relatives (CWRs) for Abiotic and Biotic Stress Tolerance

Wild relatives of cultivated plants are an extremely important component of genetic resources. Their significance for sustainable agriculture is considerable, as CWRs represent a key element of biodiversity. They constitute valuable and unique breeding material, serving as a source of effective resistance genes. High resistance to abiotic and biotic stresses is precisely the trait for which CWRs are utilized in breeding programs. Both CWRs and local varieties are characterized by their ability to adapt to marginal environments and exhibit higher resistance to pathogens [8]. The long-term co-evolution of CWRs with pathogens of varying virulence has contributed to the accumulation of resistance genes [55]. Wild relatives have not been subjected to intensive breeding selection, and their genetic heterogeneity combined with environmental pressures has favored the preservation of numerous desirable resistance alleles [55].

3.5. Genome Editing of Crop Wild Relatives: Advances, Applications, and Challenges

Crop wild relatives (CWRs) are a key source of unique genes that confer resistance to diseases, pests, and tolerance to abiotic stresses such as drought, salinity, and high temperatures [56,57]. Traditional transfer of these traits to cultivated varieties is time-consuming, hampered by cross-breeding barriers and the risk of introducing undesirable characteristics [58,59]. The development of genome editing techniques, including CRISPR-Cas9, enables the precise introduction of beneficial alleles identified in CWRs without the need for lengthy crossbreeding. This allows for the rapid enrichment of the genetic pool of crops with traits that increase resistance and yield stability under climate change conditions [60].

The selection of suitable CWR material is a significant challenge that can be supported by algorithmic analyses and machine learning [61,62,63]. The use of satellite data or drones allows for rapid screening of wild populations and assessment of genetic resources. Genetic resources include not only physical material but also data characterizing and phenotyping CWRs. Making data available at the accession level, including digital DNA sequences, is critical for fully exploiting the potential of CWRs and modern genome editing technologies [64,65,66].

Using digital DNA sequence information and precise genome editing techniques such as CRISPR/Cas9, it is possible to modify genes in available plant genetic resources (PGRs) to obtain desired domesticated traits. The CRISPR/Cas9 system uses a single RNA guide to direct the enzyme complex to the target DNA sequence, inducing double-strand breaks [67,68,69]. Various tools then enable the required changes to the DNA, for example, through base editors that alter specific nucleotides and amino acids [70]. Cas9 variants without PAM requirements increase flexibility in target selection [71], and prime editing enables precise nucleotide changes in the protospacer region, including larger integrations in twin prime editing [72]. Multiplexing allows multiple targets to be edited simultaneously, limited only by the size of the plasmid [66,73].

Genome editing using CRISPR/Cas9 in barley is already well established. Kapusi et al. (2017) [74] induced deletions in the ENGase gene, and Holme et al. (2017) [75] neutralized the HvPAPhy_a gene encoding phytase. CRISPR/Cas has also expanded knowledge of lignin modification [76], vitamin E biosynthesis [77], and protein function [78]. Panting et al. (2021) [79] modified barley to produce recombinant proteins. Evidence from de novo domestication and domestication of CWR receptors in tomato, edible physalis, and allopolyploid rice demonstrates the potential impact of these new technologies [80,81,82].

Examples of de novo domestication of CWRs highlight the enormous potential of this technology. In wild tomato, editing several domestication genes resulted in a T1 generation with ten times more fruits, three times larger fruits, and five times higher lycopene content [60]. Similar successes have been reported in edible physalis, where plant architecture and yield were improved, and in wild allopolyploid rice, where homologous genes associated with domestication and agronomic traits were modified. In contrast, undesirable characteristics such as high seed shattering and long awns were removed [28].

Despite its great potential, CWR genome editing faces challenges, such as limited knowledge of the genomes of many wild relatives, difficulties in accessing genetic and genomic resources, lack of well-established genetic transformation systems, and the need to characterize gene expression profiles. The success of de novo domestication also depends on the precise selection of material, effective multiplex editing, and integration of genotypic, phenotypic, and sequential data to maximize the use of CWR resources. Transformability remains a major barrier, particularly in barley, where research is mainly conducted on the ‘Golden Promise’ variety due to its good regeneration [83,84,85]. Success has been achieved using the barley germplasm system [86], but the method needs to be optimized for wild barley.

De novo domestication represents a novel approach for developing crop species with a broad genetic base, increased resistance to environmental stresses, and improved nutritional value [56,57,58,59,60]. Progress in this area will largely depend on the pace of characterization of CWRs and integration into the breeding program.

3.6. Summary of Genetic Diversity for Sustainable Agriculture

Wild crop relatives (CWRs) are a key source of genetic diversity, essential for sustainable agriculture. They provide valuable and effective genes for resistance to biotic stresses and tolerance to abiotic stresses. They carry crucial traits that, among other things, improve tolerance to drought stress and extreme environmental conditions. However, the widespread use of CWRs faces biological and genetic barriers.

The conservation of CWRs through in situ and ex situ strategies is crucial for maintaining biodiversity and food security. Gene banks play a central role in this process. It is estimated that more than 6 million genetic resources are stored worldwide. This is our heritage, and it must be protected. Global warming poses a significant threat to CWRs, and many wild species are increasingly vulnerable to climate change and progressive genetic erosion.

Modern genome editing technologies, in particular the CRISPR/Cas9 system, have revolutionized the use of CWRs. The precise transfer of desired traits to breeding varieties in resistance breeding is extremely important. New crop varieties that have better adapted to changing environmental conditions have been developed. This is an important step towards organic farming and sustainable food production worldwide.

4. Genetic Resistance as a Basis for Sustainable Wheat and Barley Production

Understanding the genetic sources of resistance in wheat and barley is a key element of strategies aimed at increasing crop stability and productivity under changing environmental conditions. This chapter presents both wild ancestors and local varieties as the foundations for breeding varieties resistant to disease and abiotic stresses. An overview of resistance genes and their introduction into cultivated varieties, along with the role of variety mixtures in agricultural practice, provides a more comprehensive understanding of the mechanisms that enhance resistance and genetic diversity. The inclusion of this chapter directly relates to the hypothesis of the work, which assumes that integrating genetic sources of resistance with breeding practices can lead to more resilient and sustainable cereal production systems.

The breakdown of resistance by pathogens and the acquisition of effective genes are closely linked key issues in plant breeding. Breaking resistance by pathogens is a fundamental problem of resistance breeding, requiring the continuous introduction and search for genes that determine stable and long-lasting resistance to relevant stress factors. The main challenges in resistance breakdown include the emergence of new pathotypes capable of overcoming previously resistant varieties and the appearance of new physiological pathogens. To overcome these challenges, breeding often employs a pyramiding strategy, which involves the accumulation of effective resistance genes in a single genotype to ensure comprehensive resistance [8,87,88].

Mechanisms limiting resistance breakthrough include the use of population (local) varieties in non-pollinated species such as rye. Local varieties, as dynamic and heterogeneous populations, contain susceptible and resistant genotypes simultaneously. Such genetic diversity reduces selection pressure on pathogens, leading to lower infestation levels and slower progression of epiphytotics [8].

4.1. Wild Ancestors and Local Varieties: Foundations for Breeding Resistant Cereal Varieties

In wheat and barley breeding, the use of wild ancestors and local varieties is a key element in acquiring genes for resistance to diseases and abiotic stresses. An important source of effective resistance genes is the wild ancestor of common wheat, Triticum dicoccoides. This species provides numerous resistance genes, including those for powdery mildew of cereals and grasses (Pm16, Pm26, Pm36, Pm3k, Pm30) [89,90], as well as for leaf rust (Puccinia triticina) and yellow rust (P. striiformis). The Yr36 gene, which confers durable resistance to yellow rust, is particularly valuable for breeding resistant common wheat [91]. The tetraploid species T. timopheevii is used in breeding programs as a source of resistance to stem rust (Sr36 gene) and powdery mildew (Pm37 gene) [38]. The use of tertiary pool species has enabled the introduction of numerous stem rust resistance genes, including Sr24 from Thinopyrum ponticum and Sr38 from T. ventricosa [92]. Combinations of resistance genes (Sr24, Sr25, Sr26, Sr32, Sr39, Sr43, Sr47, Sr51) from species such as Th. ponticum, T. speltoides and Ae. searsii were used to combat the Ug99 race. The resistance genes Yr17, Lr37 and Sr38 were introduced into the breeding material by translocation [93]. The resistance gene Pm21, considered one of the most effective against B. graminis f. sp. tritici, comes from Haynaldia villosa (syn. Dasypyrum villosum) [94,95]. Thanks to genetic engineering, the leaf rust resistance genes Lr9 (Ae. umbellulata), Lr19, Lr24, Lr29 (Agropyron elongatum), Lr21 (Ae. tauschii) and Lr28 (Ag. intermedium) have also been introduced into wheat [92,96].

In barley (Hordeum vulgare L.), the primary gene pool includes diverse local cultivars and its diploid ancestor, H. vulgare ssp. spontaneum, which provides important resistance genes. It provides important resistance genes. Tolerance genes for barley yellow dwarf virus (BYDV–MAV, BYDV–PAV, CYDV–RPV) were identified in Ethiopian local cultivars, including Ryd2 and Ryd3 [97]. Resistance to barley leaf rust (Rph1 and Rph2) was detected in the cultivar Egypt 4 and in hybrids with H. spontaneum [98]. Primitive local cultivars from the Mediterranean basin are valuable sources of powdery mildew resistance (B. graminis f. sp. hordei) [99,100]. Alleles from the primary gene pool can be introduced into breeding programs through crossbreeding with elite cultivars [101]. However, hybrid lines rarely surpass elite cultivars in productivity, requiring multiple backcrosses to restore recipient traits [102].

4.2. Application of Resistant Varieties in Integrated Crop Management

The rules and guidelines of Integrated Plant Protection (IPP) emphasize the use of all possible and available methods aimed at reducing the development of harmful organism populations to levels that do not cause economic damage. IPP underlines the importance of research on plant diseases and breeding resistance, as well as more extensive use of varieties resistant to diseases in production conditions.

Disease-resistant varieties play a crucial role in crop cultivation and protection. It is predicted that in the coming years, their importance will significantly increase—not only within the framework of IPP, but also in relation to the need for diverse and sustainable agricultural management systems. More extensive use of varieties resistant to biotic and abiotic stress in production practice, including IPP, is going to require closer-than-before cooperation between plant cultivators, research institutions and entities devoted to variety and agricultural experimentation.

4.3. Role of Variety Mixtures in Enhancing Genetic Diversity and Disease Resilience

Modern cereal cultivation relies on intensive conventional farming and the continuous modernization of production technologies. Unfortunately, this also leads to the undesirable phenomenon of narrowing the genetic pool of cultivated plants. Large farms usually grow the same species and even varieties of crops. Although this simplifies farm management, it reduces biodiversity and increases crop susceptibility to diseases and pests. The greater sensitivity of cultivated varieties to environmental changes is also significant. The selection of one or two varieties with similar disease resistance promotes the rapid spread of single physiological strains of pathogens. One of the most cost-effective and relatively simple methods to diversify production and simultaneously increase the durability of genetic resistance in modern varieties under production conditions is to grow them in various types of variety mixtures [103,104,105,106], and recently complex interbred populations, created in line with the concept of evolution in plant breeding [107].

Variety mixture cultivation refers to both inter-species mixtures (cereal-pulse, cereal-cereal) and inter-variety mixtures within the same species, mainly cereals. The cultivation of cereals in mixed varieties primarily increases biodiversity. Thanks to the different characteristics of the selected varieties, the natural diversity of the environment is better and more effectively utilized. This allows for better use and sustainable development of agriculture. In genetically diverse mixtures, we observe various biological (genetic and epidemiological) and ecological mechanisms that limit diseases [103,104,105,108,109,110,111] monocultures of varieties. Resistant plants growing between susceptible varieties are a natural ‘barrier’ to the spread of pathogens. Other phenomena include induced resistance or interactions between diseases (epidemics) and ecological factors (complementation, compensation, competition, aggression, and tolerance). Variety mixtures also play a key role at the farm level. First and foremost, they influence biodiversity, natural adaptation to climate change and the evolution of a given population in specific environmental conditions. Such adaptation influences the selection of only those genotypes that are best suited to the given environmental conditions. In addition, genotypes selected through natural evolution are an effective and sustainable source of disease resistance and long-term crop stability [112].

4.4. Summary: Genetic Resistance as a Basis for Sustainable Wheat and Barley Production

Species such as Triticum dicoccoides, T. timopheevii, and Hordeum vulgare ssp. spontaneum have facilitated the introduction of genes conferring resistance to major fungal diseases of cereals, including powdery mildew of cereals and grasses. Progress in the identification and transfer of resistance genes to breeding varieties/lines has developed resistance breeding that is also geared towards changing environmental conditions.

Variety mixtures also play an important role. Greater genetic diversity significantly limits the development of pathogens, improves crop stability, and promotes the efficient use of environmental resources. In the context of climate change, genetically diverse populations are better adapted to local environmental conditions. Consequently, the long-term resistance of breeding materials and the sustainable development of agriculture are ensured. In this way, the long-term resistance of breeding material and the sustainable development of agriculture are ensured.

The synergy between genetic resources and the practice of variety mixtures creates a synergistic model for breeding resistant varieties. The integration of these two breeding strategies enhances varietal resistance, ensures yield stability, and supports the adaptation of crops while promoting the resilience of sustainable agroecosystems under changing climatic conditions.

5. Benefits of Variety Mixtures

The cultivation of cereals in mixed crops offers the advantage of reducing the need for costly chemical treatments. It represents a relatively simple, low-cost, and, above all, environmentally friendly approach. Genetic diversity allows for better use of the natural habitat resources of a particular plantation, which translates into higher and more stable yields.

Studies on the effects of variety mixtures on Blumeria graminis f. sp. hordei populations have shown that, due to diversified genetic resistance, these mixtures exert a stabilizing effect on pathogen population structure. In variety mixtures, unlike in the case of single varieties, the pathogen strains show a more complex spectrum of pathogenicity [106,113,114]. What is more, populations of pathogens in variety mixtures are more diverse in terms of pathogenicity, thus a field with a mixture is not as favourable for the fast development of single strains of pathogen populations [115,116]. As a consequence, cultivation of variety mixtures slows down the phenomenon of breakdown of resistance of varieties [103,108]. The selection of variety mixtures, both inter-species and inter-varietal, cannot be random. Determining the composition of a mixture shall be preceded by epidemiological research of the pathogen population, as well as examination of genetic resistance to diseases of potential variety mixture components [103,113,115]. It is, thus, necessary to conduct field research aimed at determining and verifying the suitability for cultivation in variety mixtures of the commercial varieties of cultivated plants available on the market [117,118].

Varieties included in a mixture should possess appropriate growth characteristics, agronomic traits, productivity, and adaptability, enabling them to perform well under mixed-crop conditions [114,115,117]. An important criterion in the selection of varieties for a mixture is the diversity in the types of genetic resistance to major diseases. A mixture should contain varieties (species) of different genetic resistance to the most important diseases and ones that are suitable for cultivation in environmental conditions of variety mixture production [108,114,117].

Due to their increased genetic diversity, variety mixtures typically produce higher and more stable yields compared with monocultures of their component varieties [103,105,106,119,120,121]. Moreover, they are less sensitive to unfavourable environmental conditions such as weather fluctuations. They are also more resistant to biotic stresses (diseases, pests, weeds) and abiotic stresses [104,109,120].

In conclusion, the main advantages of mixed cropping include ease of implementation, enhanced biodiversity within the crop, reduced reliance on costly chemical treatments, and stable yields.

6. The Role of Genetic Resources and Variety Mixtures in Diversified Agriculture

The synergy between genetic resources and variety mixtures within diversified agriculture plays an important role in preserving biodiversity (Figure 2). In addition, an integrated approach supports the ecological functions of agroecosystems which is particularly relevant in the context of Evolutionary Participatory Breeding (EPB) [112,122].

Furthermore, in the face of climate change and the intensification of agriculture, the role of genetic resources and variety mixtures is becoming increasingly important.

EPB is an ecological breeding approach that combines the adaptive potential of evolutionary populations with decentralized participatory plant breeding (PPB) programs [123,124]. Based on the available literature, effective improvements in selection and adaptive indices have been reported [125,126,127].

A key component of these efforts is on-farm conservation. The activities undertaken as part of the LIVESEED project are noteworthy. The main objective of the project is to expand organic breeding and seed production throughout Europe. The LIVESEED project primarily involves research aimed at adapting local varieties to specific environmental conditions and addressing the shortage of organic varieties in crops. The project promotes the development and use of ‘organic heterogeneous material’ and ‘organic varieties suitable for organic production’ using a participatory approach such as EPB. Such a comprehensive approach will ensure protection and long-term genetic diversity, as well as the autonomy of organic farming throughout Europe [128,129]. The example of the LIVESEED project is included to illustrate how practical applications of on-farm conservation and participatory breeding can enhance genetic diversity and support the resilience of diversified agricultural systems.

On-farm conservation plays the most important role in participatory breeding. This process involves adapting genotype mixtures to a specific environment. As a result, this approach ensures a high diversity of cultivated varieties. Plant material is diverse in terms of tolerance to abiotic characteristics, resistance to biotic factors, and adaptability to local environmental conditions. Over time, as a result of natural selection, genotypes best suited to local environments become dominant [112].

Local varieties, often referred to as landraces or traditional cultivars, are a key component of local agrobiodiversity. Local diversity of varieties and species is one of the fundamental elements of sustainable agriculture. It includes local, old, and amateur varieties. The cultivation of local varieties ensures the preservation of biodiversity. Although they are characterized by lower yields compared to cultivated varieties, they are an effective source of resistance genes and a vehicle for adaptation to changing weather conditions [8,130]. Local varieties are unique plant material, cultivated on small farms, with little external input and in a highly diverse environment [131]. This material should be nurtured and protected from extinction (erosion). In an era of climate change and intensification of agriculture, the preservation of local genetic diversity is at risk [8,130].

Local varieties are divided into two main types [132]. Primary local varieties were created as a result of repeated in situ selection, without formal breeding, and may be autochthonous (developed in the region where they are grown) or allochthonous (transferred from another location after prior adaptation). Secondary local varieties have been officially improved through breeding, but are now maintained and reproduced in situ through agricultural selection and seed saving [132].

Crop mixtures and other forms of in situ (on-site) and on-farm conservation are extremely important and complementary to ex situ conservation in gene banks. While gene banks preserve resources in a static manner, mixtures in farmers’ fields allow for dynamic evolution and selection [112,122]. Only a combination of both conservation methods guarantees the full safety and protection of crop biodiversity.

Currently, numerous initiatives are being implemented to collect and conserve plant genetic resources. Gene banks play a vital role in this process, supported by developed and internationally agreed political and legal frameworks that regulate the protection and management of genetic resources worldwide.

In summary, mixtures of genotypes of the same crop are an active form of utilization and conservation of plant genetic resources. Continuous evolution and adaptation to specific environmental conditions complement ex situ conservation methods [112,122]. Synergy between genetic resources and variety mixtures plays an important role in adaptation to climate change and agricultural programs.

7. Conclusions

In the face of climate change and intensification of agriculture, biodiversity conservation plays a very important role. The wild relatives of cultivated plants and local varieties are a valuable and effective genetic resource (unique genetic background). They are a source of effective and sustainable carriers of resistance to biotic stress and tolerance to abiotic stress. Effective use of CWRs promotes the stabilization of yields of modern crop varieties and has a positive effect on reducing dependence on chemical plant protection products. Combining CWR-based breeding with variety mixtures and participatory plant selection allows for the creation of evolutionarily resistant cropping systems that adapt to local conditions and support genetic diversity at the farm level.

The conservation of genetic resources requires the simultaneous use of in situ and ex situ strategies. Gene banks located around the world play a unique role in this process. In addition, dynamic field conservation, together with the preservation of crop biodiversity, ensures both ecosystem protection and long-term food security. The use of variety mixtures in agricultural practice increases genetic diversity, stabilizes yields, and reduces pressure from pathogens and pests. This approach contributes in a practical way to more sustainable and rational agricultural production.

The practical conclusions drawn from this manuscript are relevant for both breeders and farmers. The simultaneous use of valuable and effective resistance carriers in resistance breeding and agricultural practice ensures the effective and rational use of genetic resources. The synergy of CWRs, variety mixtures, and participatory plant selection should be promoted and supported by EU agricultural policy. This research direction primarily promotes the protection of biodiversity. In addition, it contributes to more effective adaptation of agricultural systems to changing climate conditions and reduces the use of chemical plant protection products in crops. In conclusion, we would like to point out that the synergistic use of genetic diversity and variety mixtures contributes to sustainable and more efficient agriculture, which in turn has a positive impact on the protection of unique natural heritage for future generations.