Woolly apple aphid (WAA, Eriosoma lanigerum Hausmann) (Hemiptera: Aphididae) is a major pest of apple trees (Malus domestica, order Rosales) and is critical to the economics of the apple industry in most parts of the world. Here, we generated a chromosome‐level genome assembly of WAA—representing the first genome sequence from the aphid subfamily Eriosomatinae—using a combination of 10X Genomics linked‐reads and in vivo Hi‐C data. The final genome assembly is 327 Mb, with 91% of the assembled sequences anchored into six chromosomes. The contig and scaffold N50 values are 158 kb and 71 Mb, respectively, and we predicted a total of 28,186 protein‐coding genes. The assembly is highly complete, including 97% of conserved arthropod single‐copy orthologues based on Benchmarking Universal Single‐Copy Orthologs (busco) analysis. Phylogenomic analysis of WAA and nine previously published aphid genomes, spanning four aphid tribes and three subfamilies, reveals that the tribe Eriosomatini (represented by WAA) is recovered as a sister group to Aphidini + Macrosiphini (subfamily Aphidinae). We identified syntenic blocks of genes between our WAA assembly and the genomes of other aphid species and find that two WAA chromosomes (El5 and El6) map to the conserved Macrosiphini and Aphidini X chromosome. Our high‐quality WAA genome assembly and annotation provides a valuable resource for research in a broad range of areas such as comparative and population genomics, insect–plant interactions and pest resistance management.
Bitter pit is one of the most economically-important physiological disorders affecting apple fruit production, causing soft discrete pitting of the cortical flesh of the apple fruits, which renders them unmarketable. The disorder is heritable, however the environment and cultural practices play a major role in expression of symptoms. Bitter pit has been shown to be controllable to a certain extent using calcium sprays and dips, however, their use does not entirely prevent the incidence of the disorder.Previously, bitter pit has been shown to be controlled by two dominant genes, and markers on linkage group 16 of the apple genome were identified that were significantly associated with the expression of bitter pit symptoms in a genome wide association study. In this investigation, we identified a major QTL for bitter pit defined by two microsatellite (SSR) markers. The association of the SSRs with the bitter pit locus, and their ability to predict severe symptom expression, was confirmed through screening of individuals with stable phenotypic expression from an additional mapping progeny. The data generated in this current study suggest a two gene model could account for the control of bitter pit symptom expression, however, only one of the loci was detectable, most likely due to dominance of alleles carried by both parents of the mapping progeny used. The SSR markers identified are costeffective, robust and multi-allelic and thus should prove useful for the identification of seedlings with resistance to bitter pit using marker assisted selection in apple breeding programs.
Sweet cherry (Prunus avium L.) is a temperate fruit species whose production might be highly impacted by climate change in the near future. Diversity of plant material could be an option to mitigate these climate risks by enabling producers to have new cultivars well adapted to new environmental conditions. In this study, subsets of sweet cherry collections of 19 European countries were genotyped using 14 SSR. The objectives of this study were (i) to assess genetic diversity parameters, (ii) to estimate the levels of population structure, and (iii) to identify germplasm redundancies. A total of 314 accessions, including landraces, early selections, and modern cultivars, were monitored, and 220 unique SSR genotypes were identified. All 14 loci were confirmed to be polymorphic, and a total of 137 alleles were detected with a mean of 9.8 alleles per locus. The average number of alleles (N = 9.8), PIC value (0.658), observed heterozygosity (Ho = 0.71), and expected heterozygosity (He = 0.70) were higher in this study compared to values reported so far. Four ancestral populations were detected using STRUCTURE software and confirmed by Principal Coordinate Analysis (PCoA), and two of them (K1 and K4) could be attributed to the geographical origin of the accessions. A N-J tree grouped the 220 sweet cherry accessions within three main clusters and six subgroups. Accessions belonging to the four STRUCTURE populations roughly clustered together. Clustering confirmed known genealogical data for several accessions. The large genetic diversity of the collection was demonstrated, in particular within the landrace pool, justifying the efforts made over decades for their conservation. New sources of diversity will allow producers to face challenges, such as climate change and the need to develop more sustainable production systems.
Woolly apple aphid (WAA, Eriosoma lanigerum Hausmann) (Hemiptera: Aphididae), is a major pest of apple trees (Malus domestica, order Rosales) and is critical to the economics of the apple industry in most parts of the world. Here, we generated a chromosome-level genome assembly of WAA -representing the first genome sequence from the aphid subfamily Eriosomatinae -using a combination of 10X Genomics linked-reads and in vivo Hi-C data.The final genome assembly is 327 Mb, with 91% of the assembled sequences anchored into six chromosomes. The contig and scaffold N50 values are 158 kb and 71 Mb, respectively, and we predicted a total of 28,186 protein-coding genes. The assembly is highly complete, including 97% of conserved arthropod single-copy orthologues based on BUSCO analysis.Phylogenomic analysis of WAA and nine previously published aphid genomes, spanning four aphid tribes and three subfamilies, reveals that the tribe Eriosomatini (represented by WAA) is recovered as a sister group to Aphidini + Macrosiphini (subfamily Aphidinae). We identified syntenic blocks of genes between our WAA assembly and the genomes of other aphid species and find that two WAA chromosomes (El5 and El6) map to the conserved Macrosiphini and Aphidini X chromosome. Our high-quality WAA genome assembly and annotation provides a valuable resource for research in a broad range of areas such as comparative and population genomics, insect-plant interactions and pest resistance management.
Background Apple replant disease (ARD) is a phenomenon associated with poor tree establishment at sites where the same, or a closely-related species, has grown for at least 1–2 years. No single organism has been identified as the universal causal agent, but there is increasing evidence that multiple soil-borne plant pathogenic fungi and oomycetes form an ARD disease complex. Root damage caused by root lesion nematodes has also been implicated in facilitating the entry of pathogens into root tissues resulting in the development of severe ARD. Methods We used a reductionist approach to determine effects of one or more members of the ARD complex on ARD in a number of selected rootstock genotypes with contrasting characteristics. Through a 15-month pot-based experiment in which semi-selective biocides were applied to soil from a replant orchard, we investigated (1) the nature of the interactions (i.e. antagonistic, additive or synergistic) between different groups of soil biota and ARD severity, and (2) whether rootstock characteristics modify ARD severity. Results There might be competitive interactions between oomycetes and fungal pathogens in infecting apple roots and hence subsequent ARD development. Controlling all three ARD components (oomycetes, fungi, and nematodes) led to the best root development. However, these effects on root development were not manifested in the above-ground tree development 15 months after treatment. Specific soil biocide treatments against fungi and oomycetes led to large changes in soil microbial communities whereas the nematicide treatment led to least changes. In spite of the observed ARD, comparing rhizosphere microbial sequences among treatments failed to reveal candidate pathogens for ARD. Conclusions Candidate ARD oomycetes and fungal pathogens are likely to engage in competitive interactions among themselves in infecting apple roots. Although soil amendments affected soil microbiota, such effects appear to be very unpredictable.
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