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In wheat, a lack of genetic diversity between breeding lines has been recognized as a significant block to future yield increases. Species belonging to bread wheat's secondary and tertiary gene pools harbour a much greater level of genetic variability, and are an important source of genes to broaden its genetic base. Introgression of novel genes from progenitors and related species has been widely employed to improve the agronomic characteristics of hexaploid wheat, but this approach has been hampered by a lack of markers that can be used to track introduced chromosome segments. Here, we describe the identification of a large number of single nucleotide polymorphisms that can be used to genotype hexaploid wheat and to identify and track introgressions from a variety of sources. We have validated these markers using an ultra‐high‐density Axiom® genotyping array to characterize a range of diploid, tetraploid and hexaploid wheat accessions and wheat relatives. To facilitate the use of these, both the markers and the associated sequence and genotype information have been made available through an interactive web site.

• The control of stem canker disease of Brassica napus (rapeseed), caused by the fungus Leptosphaeria maculans is based largely on plant genetic resistance: single-gene specific resistance (Rlm genes) or quantitative, polygenic, adult-stage resistance. Our working hypothesis was that quantitative resistance partly obeys the gene-for-gene model, with resistance genes ‘recognizing’ fungal effectors expressed during late systemic colonization. • Five LmSTEE (stem-expressed effector) genes were selected and placed under the control of the AvrLm4-7 promoter, an effector gene highly expressed at the cotyledon stage of infection, for miniaturized cotyledon inoculation test screening of a gene pool of 204 rapeseed genotypes. • We identified a rapeseed genotype, ‘Yudal’, expressing hypersensitive response to LmSTEE98. The LmSTEE98–RlmSTEE98 interaction was further validated by inactivation of the LmSTEE98 gene with a CRISPR-Cas9 approach. Isolates with mutated versions of LmSTEE98 induced more severe stem symptoms than the wild-type isolate in ‘Yudal’. This single-gene resistance was mapped in a 0.6 cM interval of the ‘Darmor_bzh’ × ‘Yudal’ genetic map. • One typical gene-for-gene interaction contributes partly to quantitative resistance when L. maculans colonizes the stems of rapeseed. With numerous other effectors specific to stem colonization, our study provides a new route for resistance gene discovery, elucidation of quantitative resistance mechanisms and selection for durable resistance.

Comparative whole-genome analyses have demonstrated that horizontal gene transfer (HGT) provides a significant contribution to prokaryotic genome innovation. The evolution of specific prokaryotes is therefore tightly linked to the environment in which they live and the communal pool of genes available within that environment. Here we use the term supergenome to describe the set of all genes that a prokaryotic 'individual' can draw on within a particular environmental setting. Conjugative plasmids can be considered particularly successful entities within the communal pool, which have enabled HGT over large taxonomic distances. These plasmids are collections of discrete regions of genes that function as 'backbone modules' to undertake different aspects of overall plasmid maintenance and propagation. Conjugative plasmids often carry suites of 'accessory elements' that contribute adaptive traits to the hosts and, potentially, other resident prokaryotes within specific environmental niches. Insight into the evolution of plasmid modules therefore contributes to our knowledge of gene dissemination and evolution within prokaryotic communities. This communal pool provides the prokaryotes with an important mechanistic framework for obtaining adaptability and functional diversity that alleviates the need for large genomes of specialized 'private genes'.

• Powdery mildew, a fungal disease caused by Blumeria graminis f. sp. tritici (Bgt), has a serious impact on wheat production. Loss of resistance in cultivars prompts a continuing search for new sources of resistance. • Wild emmer wheat (Triticum turgidum ssp. dicoccoides, WEW), the progenitor of both modern tetraploid and hexaploid wheats, harbors many powdery mildew resistance genes. We report here the positional cloning and functional characterization of Pm41, a powdery mildew resistance gene derived from WEW, which encodes a coiled-coil, nucleotide-binding site and leucine-rich repeat protein (CNL). Mutagenesis and stable genetic transformation confirmed the function of Pm41 against Bgt infection in wheat. • We demonstrated that Pm41 was present at a very low frequency (1.81%) only in southern WEW populations. It was absent in other WEW populations, domesticated emmer, durum, and common wheat, suggesting that the ancestral Pm41 was restricted to its place of origin and was not incorporated into domesticated wheat. • Our findings emphasize the importance of conservation and exploitation of the primary WEW gene pool, as a valuable resource for discovery of resistance genes for improvement of modern wheat cultivars.

Saffron crocus (Crocus sativus) is the source of the most expensive spice of the world, produced from manually harvested stigmas, thus serving as a cash crop for rural communities. However, despite its economic importance, its genome and chromosomes are poorly studied. C. sativus is a sterile triploid species harboring eight chromosome triplets, and propagated only as a clonal lineage by corms. Saffron’s evolutionary origin, parental species and allo- or autotriploidy has been a matter of discussion for almost a century. We performed a survey sequencing of the saffron genome and selected cytogenetic land-mark sequences consisting of major tandem repeats, which we used as probes in comparative multicolor fluorescent in situ hybridization (FISH). We tagged 92 chromosomal positions and resolved the chromosomal composition of saffron triplets. By comparative FISH of six Crocus species from 11 accessions, we demonstrate that C. sativus is an autotriploid hybrid derived from heterogeneous Crocus cartwrightianus cytotypes. The FISH reference karyotype of saffron is crucial for integrating genome sequencing data with chromosomes and for investigating the relationship among Crocus species. We provide an evolutionary model of the saffron emergence; the knowledge of the parental origin offers a route towards the resynthesis of C. sativus from C. cartwrightianus to broaden saffron’s gene pool.

We have studied the nucleotide diversity of common bean, Phaseolus vulgaris, which is characterized by two independent domestications in two geographically distinct areas: Mesoamerica and the Andes. This provides an important model, as domestication can be studied as a replicate experiment. We used nucleotide data from five gene fragments characterized by large introns to analyse 214 accessions (102 wild and 112 domesticated). The wild accessions represent a cross-section of the entire geographical distribution of P. vulgaris. A reduction in genetic diversity in both of these gene pools was found, which was three-fold greater in Mesoamerica compared with the Andes. This appears to be a result of a bottleneck that occurred before domestication in the Andes, which strongly impoverished this wild germplasm, leading to the minor effect of the subsequent domestication bottleneck (i.e. sequential bottleneck). These findings show the importance of considering the evolutionary history of crop species as a major factor that influences their current level and structure of genetic diversity. Furthermore, these data highlight a single domestication event within each gene pool. Although the findings should be interpreted with caution, this evidence indicates the Oaxaca valley in Mesoamerica, and southern Bolivia and northern Argentina in South America, as the origins of common bean domestication.

Background Genetic diversity is crucial for conservation efforts as well as breeding programs targeted at the development of improved varieties. Taro, a climate-resilient crop, plays a vital role in the nutritional and economic livelihoods of many households in Nigeria, but its yield is very low due to inadequate genetic improvement efforts. A diversity assessment of Nigerian taro is therefore required to create a premise for its improvement in yield, quality and disease tolerance. In this study, the genetic diversity and population structure of 490 taro cultivars comprising two main gene pools: Dasheen (215) and Eddoe (275), collected from farmers and marketers across seven states in Nigeria was assessed using 3047 Diversity Array Technology single nucleotide polymorphism (DArT-SNP) markers. A subset of 114 taro cultivars, comprising 30 Dasheens and 84 Eddoes were further phenotyped using 24 agro-morphological descriptors. Results Both phenotypic and molecular characterization revealed higher genetic diversity among the Eddoes than Dasheens. Estimates of gene flow (Nm = 0.353) revealed intermixing of cultivars among the States of collection, with the highest gene flow occurring between cultivars from Anambra and Ondo states and the lowest between Anambra and Kwara states. Population structure and Ward’s minimum variance hierarchical cluster based on DArT-SNPs identified four groups, one comprising Dasheen and three comprising Eddoe cultivars. Hierarchical clustering based on phenotypic traits delineated three clusters. Variation between gene pools (49%) was higher than within gene pools (32%). Variation among States of collection was high (41%), while variation among individuals within gene pools (18%) and States of collection (19%) was relatively low. Correlation between phenotypic and genotypic diversity assessments was low ( r  = 0.01), indicating that both approaches were necessary for assessing genetic diversity in taro. However, genotypic assessment provided better information about genetic diversity of the taro cultivars. Conclusion This is the first study that represented germplasm collection across the major taro growing regions of Nigeria. The findings from this study based on agro-morphological characterization and DArT-SNP genotyping are critical for genetic characterization, conservation and breeding of taro in Nigeria, mainly initiating hybridization between the two genepools after careful assessment of ploidy levels of the accessions collected in this study. This will facilitate in developing improved taro varieties with desirable traits, such as higher yield, better disease resistance, and improved nutritional quality.

Maintenance of standing genetic diversity and effective population size (Ne) in trees is essential for sustainability, adaptation, and evolution, especially for dioecious tree species under changed climatic conditions. We examined the gene pool of Taxus baccata along latitudinal gradients in the Hyrcanian forest from west to east using 15 simple sequence repeat markers (SSR). A high level of genetic diversity and a significant level of fixation index was observed, and the populations showed spatial genetic structure. The fixation index ranged from 0.027 to 0.197. In six out of eleven populations inbreeding was the significant factor influencing deviation from the Hardy–Weinberg equilibrium. There was no bottleneck effect in any of the analysed populations and the global Fst with ENA correction was 0.044. The average total number of migrants per generation ranged from 4.93 to 2.14. Under the six tested scenarios, the DIYABC analysis showed that the eastern and western parts of the Hyrcanian yew forests split about 134 generations ago but these two pools meet in the central part of these forests about 49 generations ago. Although the genetic diversity of T. baccata in the Hyrcanian forest is relatively high, it is expected that the inbreeding depression will increase over time, causing the accumulation of destructive alleles and intensifying the extinction process. This process is caused by anthropogenic activities, habitat fragmentations, the age of the trees, low regenerations, the existence of high geographical barriers, and a significant reduction in gene flow among the habitats.

Lima bean ( Phaseolus lunatus L.) is composed of two major gene pools. The Andean gene pool gave rise to the Gran Lima cultigroup, and the Mesoamerican gene pool gave rise to the Papa and Sieva cultigroups. In the Yucatan Peninsula, Lima bean presents a great diversity of landraces that belong to the Mesoamerican gene pool. However, studies so far have not been able to determine whether the Papa and Sieva cultigroup germplasm resources managed by Maya farmers can be morphologically or genetically differentiated. In addition, the physiological seed quality traits of P. lunatus are still unknown. Therefore, the objectives of the study were: (1) To evaluate morphological differentiation of the Papa and Sieva cultigroups of Lima bean and (2) To evaluate the physiological seed quality based on standard germination and emergence of seedlings tests. Results showed two well-defined groups. Group A comprised landraces JMC1288, JMC1336, JMC1364 and JMC1271 belonging to the Sieva cultigroup; group B included landraces JMC1208, JMC1264, JMC1313 and JMC1337 belonging to the Papa cultigroup. The germination percentage was 84%, and rate was 15 seeds germinated d −1 . The percentage of seedling emergence was 86%, and seedling emergence rate was 14 emerged seedlings d −1 . Results confirmed the presence of the Papa and Sieva cultigroups in the Yucatan Peninsula. The landraces of Papa cultigroup produced seeds with the best physiological quality for use in breeding and conservation programmes.

Patterns of genetic variation in crops are the result of multiple processes that have occurred during their domestication and improvement, and are influenced by their wild progenitors that often remain understudied. The locoto chile, Capsicum pubescens , is a crop grown mainly in mid-highlands of South-Central America. This species is not known from the wild and exists only as a cultigen. The evolutionary affinities and exact origin of C. pubescens have still not been elucidated, with hypotheses suggesting its genetic relatedness and origin to two wild putative ancestral Capsicum species from the Central Andes, C. eximium and C. cardenasii . In the current study, RAD-sequencing was applied to obtain genome-wide data for 48 individuals of C. pubescens and its wild allies representing different geographical areas. Bayesian, Maximum Likelihood and coalescent-based analytical approaches were used to reconstruct population genetic patterns and phylogenetic relationships of the studied species. The results revealed that C. pubescens forms a well-defined monotypic lineage closely related to wild C. cardenasii and C. eximium , and also to C. eshbaughii . The primary lineages associated with the diversification under domestication of C. pubescens were also identified. Although direct ancestor-descendant relationship could not be inferred within this group of taxa, hybridization events were detected between C. pubescens and both C. cardenasii and C. eximium . Therefore, although hybrid origin of C. pubescens could not be inferred, gene flow involving its wild siblings was shown to be an important factor contributing to its contemporary genetic diversity. The data allowed for the inference of the center of origin of C. pubescens in central-western Bolivia highlands and for better understanding of the dynamics of its gene pool. The results of this study are essential for germplasm conservation and breeding purposes, and provide excellent basis for further research of the locoto chile and its wild relatives.