Corrigendum: How could the use of crop wild relatives in breeding increase the adaptation of crops to marginal environments?

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Prevalence and Distribution of Three Bumblebee Pathogens from the Czech Republic.

Bumblebees are significant pollinators for both wild plants and economically important crops. Due to the worldwide decrease in pollinators, it is crucial to monitor the prevalence and distribution of bumblebee pathogens. Field-caught bumblebee workers and males were examined for the presence of three pathogens during the summer months of the years 2015-2020 (Bombus terrestris/lucorum) and 2015-2017 (Bombus lapidarius). The greatest prevalence was in the case of Crithidia bombi, where significantly more workers (57%) of B. terrestris/lucorum were infected than males (41%). Infection was also confirmed in 37% of B. lapidarius workers. The average prevalence was very similar in the case of Nosema bombi in workers (25%) and males (22%) of B. terrestris/lucorum. In the case of B. lapidarius, 17% of the workers were infected. The lowest number of infected individuals was for Apicystis bombi and the prevalence of infection was significantly higher for males (22%) than workers (8%) of B. terrestris/lucorum. Only 3% of workers and 4% of males of B. terrestris/lucorum were simultaneously infected with three types of pathogens, but no worker was infected with only a combination of N. bombi and A. bombi. The greatest prevalence of C. bombi was found in urban or woodland areas.

How Could the Use of Crop Wild Relatives in Breeding Increase the Adaptation of Crops to Marginal Environments?

Alongside the use of fertilizer and chemical control of weeds, pests, and diseases modern breeding has been very successful in generating cultivars that have increased agricultural production several fold in favorable environments. These typically homogeneous cultivars (either homozygous inbreds or hybrids derived from inbred parents) are bred under optimal field conditions and perform well when there is sufficient water and nutrients. However, such optimal conditions are rare globally; indeed, a large proportion of arable land could be considered marginal for agricultural production. Marginal agricultural land typically has poor fertility and/or shallow soil depth, is subject to soil erosion, and often occurs in semi-arid or saline environments. Moreover, these marginal environments are expected to expand with ongoing climate change and progressive degradation of soil and water resources globally. Crop wild relatives (CWRs), most often used in breeding as sources of biotic resistance, often also possess traits adapting them to marginal environments. Wild progenitors have been selected over the course of their evolutionary history to maintain their fitness under a diverse range of stresses. Conversely, modern breeding for broad adaptation has reduced genetic diversity and increased genetic vulnerability to biotic and abiotic challenges. There is potential to exploit genetic heterogeneity, as opposed to genetic uniformity, in breeding for the utilization of marginal lands. This review discusses the adaptive traits that could improve the performance of cultivars in marginal environments and breeding strategies to deploy them.

Wild emmer wheat, the progenitor of modern bread wheat, exhibits great diversity in the VERNALIZATION1 gene.

Wild emmer wheat is an excellent reservoir of genetic variability that can be utilized to improve cultivated wheat to address the challenges of the expanding world population and climate change. Bearing this in mind, we have collected a panel of 263 wild emmer wheat (WEW) genotypes across the Fertile Crescent. The genotypes were grown in different locations and phenotyped for heading date. Genome-wide association mapping (GWAS) was carried out, and 16 SNPs were associated with the heading date. As the flowering time is controlled by photoperiod and vernalization, we sequenced the VRN1 gene, the most important of the vernalization response genes, to discover new alleles. Unlike most earlier attempts, which characterized known VRN1 alleles according to a partial promoter or intron sequences, we obtained full-length sequences of VRN-A1 and VRN-B1 genes in a panel of 95 wild emmer wheat from the Fertile Crescent and uncovered a significant sequence variation. Phylogenetic analysis of VRN-A1 and VRN-B1 haplotypes revealed their evolutionary relationships and geographic distribution in the Fertile Crescent region. The newly described alleles represent an attractive resource for durum and bread wheat improvement programs.

Corrigendum: American Foulbrood in the Czech Republic: ERIC II Genotype of Paenibacillus Larvae Is Prevalent.

[This corrects the article DOI: 10.3389/fvets.2021.698976.].

American Foulbrood in the Czech Republic: ERIC II Genotype of Paenibacillus Larvae Is Prevalent.

American foulbrood (AFB) is a dangerous disease of honeybees (Apis mellifera) caused by the spore-forming bacterium Paenibacillus larvae. According to the ERIC (enterobacterial repetitive intergenic consensus) classification, five genotypes are distinguished, i.e., I, II, III, IV, and V, which differ in their virulence and prevalence in colonies. In the Czech Republic, AFB prevalence is monitored by the State Veterinary Administration; however, the occurrence of specific P. larvae genotypes within the country remains unknown. In this study, our aim was to genotype field P. larvae strains collected in the Czech Republic according to the ERIC classification. In total, 102 field isolates from colonies with AFB clinical symptoms were collected from various locations in the Czech Republic, and the PCR genotypization was performed using ERIC primers. We confirmed the presence of both ERIC I and II genotypes, while ERIC III, IV, and V were not detected. The majority of samples (n = 82, 80.4%) were identified as ERIC II, while the ERIC I genotype was confirmed only in 20 samples (19.6%). In contrast to other European countries, the ERIC II genotype is predominant in Czech honeybee colonies. The ERIC I genotype was mostly detected in border regions close to Poland, Slovakia, and Austria.

Intricate Distribution Patterns of Six Cytotypes of Allium oleraceum at a Continental Scale: Niche Expansion and Innovation Followed by Niche Contraction With Increasing Ploidy Level.

The establishment and success of polyploids are thought to often be facilitated by ecological niche differentiation from diploids. Unfortunately, most studies compared diploids and polyploids, ignoring variation in ploidy level in polyploids. To fill this gap, we performed a large-scale study of 11,163 samples from 1,283 populations of the polyploid perennial geophyte Allium oleraceum with reported mixed-ploidy populations, revealed distribution ranges of cytotypes, assessed their niches and explored the pattern of niche change with increasing ploidy level. Altogether, six ploidy levels (3x-8x) were identified. The most common were pentaploids (53.6%) followed by hexaploids (22.7%) and tetraploids (21.6%). Higher cytotype diversity was found at lower latitudes than at higher latitudes (>52° N), where only tetraploids and pentaploids occurred. We detected 17.4% of mixed-ploidy populations, usually as a combination of two, rarely of three, cytotypes. The majority of mixed-ploidy populations were found in zones of sympatry of the participating cytotypes, suggesting they have arisen through migration (secondary contact zone). Using coarse-grained variables (climate, soil), we found evidence of both niche expansion and innovation in tetraploids related to triploids, whereas higher ploidy levels showed almost zero niche expansion, but a trend of increased niche unfilling of tetraploids. Niche unfilling in higher ploidy levels was caused by a contraction of niche envelopes toward lower continentality of the climate and resulted in a gradual decrease of niche breadth and a gradual shift in niche optima. Field-recorded data indicated wide habitat breadth of tetraploids and pentaploids, but also a pattern of increasing synanthropy in higher ploidy levels. Wide niche breadth of tetra- and pentaploids might be related to their multiple origins from different environmental conditions, higher "age", and retained sexuality, which likely preserve their adaptive potential. In contrast, other cytotypes with narrower niches are mostly asexual, probably originating from a limited range of contrasting environments. Persistence of local ploidy mixtures could be enabled by the perenniality of A. oleraceum and its prevalence of vegetative reproduction, facilitating the establishment and decreasing exclusion of minority cytotype due to its reproductive costs. Vegetative reproduction might also significantly accelerate colonization of new areas, including recolonization of previously glaciated areas.

Physical Dormancy Release in Medicago truncatula Seeds Is Related to Environmental Variations.

Seed dormancy and timing of its release is an important developmental transition determining the survival of individuals, populations, and species in variable environments. Medicago truncatula was used as a model to study physical seed dormancy at the ecological and genetics level. The effect of alternating temperatures, as one of the causes releasing physical seed dormancy, was tested in 178 M. truncatula accessions over three years. Several coefficients of dormancy release were related to environmental variables. Dormancy varied greatly (4-100%) across accessions as well as year of experiment. We observed overall higher physical dormancy release under more alternating temperatures (35/15 °C) in comparison with less alternating ones (25/15 °C). Accessions from more arid climates released dormancy under higher experimental temperature alternations more than accessions originating from less arid environments. The plasticity of physical dormancy can probably distribute the germination through the year and act as a bet-hedging strategy in arid environments. On the other hand, a slight increase in physical dormancy was observed in accessions from environments with higher among-season temperature variation. Genome-wide association analysis identified 136 candidate genes related to secondary metabolite synthesis, hormone regulation, and modification of the cell wall. The activity of these genes might mediate seed coat permeability and, ultimately, imbibition and germination.

Allelic Diversity of Acetyl Coenzyme A Carboxylase accD/bccp Genes Implicated in Nuclear-Cytoplasmic Conflict in the Wild and Domesticated Pea (Pisum sp.).

Reproductive isolation is an important component of species differentiation. The plastid accD gene coding for the acetyl-CoA carboxylase subunit and the nuclear bccp gene coding for the biotin carboxyl carrier protein were identified as candidate genes governing nuclear-cytoplasmic incompatibility in peas. We examined the allelic diversity in a set of 195 geographically diverse samples of both cultivated (Pisum sativum, P. abyssinicum) and wild (P. fulvum and P. elatius) peas. Based on deduced protein sequences, we identified 34 accD and 31 bccp alleles that are partially geographically and genetically structured. The accD is highly variable due to insertions of tandem repeats. P. fulvum and P. abyssinicum have unique alleles and combinations of both genes. On the other hand, partial overlap was observed between P. sativum and P. elatius. Mapping of protein sequence polymorphisms to 3D structures revealed that most of the repeat and indel polymorphisms map to sequence regions that could not be modeled, consistent with this part of the protein being less constrained by requirements for precise folding than the enzymatically active domains. The results of this study are important not only from an evolutionary point of view but are also relevant for pea breeding when using more distant wild relatives.

Variation in wild pea (Pisum sativum subsp. elatius) seed dormancy and its relationship to the environment and seed coat traits.

BACKGROUND: Seed germination is one of the earliest key events in the plant life cycle. The timing of transition from seed to seedling is an important developmental stage determining the survival of individuals that influences the status of populations and species. Because of wide geographical distribution and occurrence in diverse habitats, wild pea (Pisum sativum subsp. elatius) offers an excellent model to study physical type of seed dormancy in an ecological context. This study addresses the gap in knowledge of association between the seed dormancy, seed properties and environmental factors, experimentally testing oscillating temperature as dormancy release clue. METHODS: Seeds of 97 pea accessions were subjected to two germination treatments (oscillating temperatures of 25/15 °C and 35/15 °C) over 28 days. Germination pattern was described using B-spline coefficients that aggregate both final germination and germination speed. Relationships between germination pattern and environmental conditions at the site of origin (soil and bioclimatic variables extracted from WorldClim 2.0 and SoilGrids databases) were studied using principal component analysis, redundancy analysis and ecological niche modelling. Seeds were analyzed for the seed coat thickness, seed morphology, weight and content of proanthocyanidins (PA). RESULTS: Seed total germination ranged from 0% to 100%. Cluster analysis of germination patterns of seeds under two temperature treatments differentiated the accessions into three groups: (1) non-dormant (28 accessions, mean germination of 92%), (2) dormant at both treatments (29 acc., 15%) and (3) responsive to increasing temperature range (41 acc., with germination change from 15 to 80%). Seed coat thickness differed between groups with dormant and responsive accessions having thicker testa (median 138 and 140 µm) than non-dormant ones (median 84 mm). The total PA content showed to be higher in the seed coat of dormant (mean 2.18 mg g-1) than those of non-dormant (mean 1.77 mg g-1) and responsive accessions (mean 1.87 mg g-1). Each soil and bioclimatic variable and also germination responsivity (representing synthetic variable characterizing germination pattern of seeds) was spatially clustered. However, only one environmental variable (BIO7, i.e., annual temperature range) was significantly related to germination responsivity. Non-dormant and responsive accessions covered almost whole range of BIO7 while dormant accessions are found in the environment with higher annual temperature, smaller temperature variation, seasonality and milder winter. Ecological niche modelling showed a more localized potential distribution of dormant group. Seed dormancy in the wild pea might be part of a bet-hedging mechanism for areas of the Mediterranean basin with more unpredictable water availability in an otherwise seasonal environment. This study provides the framework for analysis of environmental aspects of physical seed dormancy.

Molecular Evidence for Two Domestication Events in the Pea Crop.

Pea, one of the founder crops from the Near East, has two wild species: Pisum sativum subsp. elatius, with a wide distribution centered in the Mediterranean, and P. fulvum, which is restricted to Syria, Lebanon, Israel, Palestine and Jordan. Using genome wide analysis of 11,343 polymorphic single nucleotide polymorphisms (SNPs) on a set of wild P. elatius (134) and P. fulvum (20) and 74 domesticated accessions (64 P. sativum landraces and 10 P. abyssinicum), we demonstrated that domesticated P. sativum and the Ethiopian pea (P. abyssinicum) were derived from different P. elatius genepools. Therefore, pea has at least two domestication events. The analysis does not support a hybrid origin of P. abyssinicum, which was likely introduced into Ethiopia and Yemen followed by eco-geographic adaptation. Both P. sativum and P. abyssinicum share traits that are typical of domestication, such as non-dormant seeds. Non-dormant seeds were also found in several wild P. elatius accessions which could be the result of crop to wild introgression or natural variation that may have been present during pea domestication. A sub-group of P. elatius overlaps with P. sativum landraces. This may be a consequence of bidirectional gene-flow or may suggest that this group of P. elatius is the closest extant wild relative of P. sativum.

Author Correction: Genomic diversity and macroecology of the crop wild relatives of domesticated pea.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Correction: Genetic structure of wild pea (Pisum sativum subsp. elatius) populations in the northern part of the Fertile Crescent reflects moderate cross-pollination and strong effect of geographic but not environmental distance.

[This corrects the article DOI: 10.1371/journal.pone.0194056.].

Genetic structure of wild pea (Pisum sativum subsp. elatius) populations in the northern part of the Fertile Crescent reflects moderate cross-pollination and strong effect of geographic but not environmental distance.

Knowledge of current genetic diversity and mating systems of crop wild relatives (CWR) in the Fertile Crescent is important in crop genetic improvement, because western agriculture began in the area after the cold-dry period known as Younger Dryas about 12,000 years ago and these species are also wild genepools of the world's most important food crops. Wild pea (Pisum sativum subsp. elatius) is an important source of genetic diversity for further pea crop improvement harbouring traits useful in climate change context. The genetic structure was assessed on 187 individuals of Pisum sativum subsp. elatius from fourteen populations collected in the northern part of the Fertile Crescent using 18,397 genome wide single nucleotide polymorphism DARTseq markers. AMOVA showed that 63% of the allelic variation was distributed between populations and 19% between individuals within populations. Four populations were found to contain admixed individuals. The observed heterozygosity ranged between 0.99 to 6.26% with estimated self-pollination rate between 47 to 90%. Genetic distances of wild pea populations were correlated with geographic but not environmental (climatic) distances and support a mixed mating system with predominant self-pollination. Niche modelling with future climatic projections showed a local decline in habitats suitable for wild pea, making a strong case for further collection and ex situ conservation.

Genomic diversity and macroecology of the crop wild relatives of domesticated pea.

There is growing interest in the conservation and utilization of crop wild relatives (CWR) in international food security policy and research. Legumes play an important role in human health, sustainable food production, global food security, and the resilience of current agricultural systems. Pea belongs to the ancient set of cultivated plants of the Near East domestication center and remains an important crop today. Based on genome-wide analysis, P. fulvum was identified as a well-supported species, while the diversity of wild P. sativum subsp. elatius was structured into 5 partly geographically positioned clusters. We explored the spatial and environmental patterns of two progenitor species of domesticated pea in the Mediterranean Basin and in the Fertile Crescent in relation to the past and current climate. This study revealed that isolation by distance does not explain the genetic structure of P. sativum subsp. elatius in its westward expansion from its center of origin. The genetic diversity of wild pea may be driven by Miocene-Pliocene events, while the phylogenetic diversity centers may reflect Pleisto-Holocene climatic changes. These findings help set research and discussion priorities and provide geographical and ecological information for germplasm-collecting missions, as well as for the preservation of extant diversity in ex-situ collections.