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The Impact of Interspecific Hybridization on Fungal Plant Pathogens: A Case Study on the Emerging Pathogen Verticillium longisporum.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	The Impact of Interspecific Hybridization on Fungal Plant Pathogens: A Case Study on the Emerging Pathogen Verticillium longisporum./
作者:	Depotter, Jasper R. L.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2018,
面頁冊數:	206 p.
附註:	Source: Dissertations Abstracts International, Volume: 83-02, Section: B.
Contained By:	Dissertations Abstracts International83-02B.
標題:	Infections. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28232997
ISBN:	9798708788030

The Impact of Interspecific Hybridization on Fungal Plant Pathogens: A Case Study on the Emerging Pathogen Verticillium longisporum.
Depotter, Jasper R. L.

The Impact of Interspecific Hybridization on Fungal Plant Pathogens: A Case Study on the Emerging Pathogen Verticillium longisporum. - Ann Arbor : ProQuest Dissertations & Theses, 2018 - 206 p.

Source: Dissertations Abstracts International, Volume: 83-02, Section: B.

Thesis (Ph.D.)--Wageningen University and Research, 2018.

Emerging plant diseases pose a threat to agricultural and natural ecosystems. Understanding the mechanisms behind such emergences is important in order to control them and prevent them from occurring in the future. Diseases can emerge because of several reasons, which are discussed in Chapter 1. Diseases emerge in pristine ecosystems through new pathogen introductions. Alternatively, alterations in the pathogen, host or environment may cause the balance of longer established plant/ pathogen interactions to shift, which may lead to the emergence of disease.Verticillium diseases cause considerable losses worldwide annually, and affect major crops such as tomato, cotton and oilseed rape. Chapter 2 focuses on one particular Verticillium pathogen, namely V. longisporum, an allodiploid species that is specialized on brassicaceous hosts. Similar to other Verticillium pathogens, V. longisporum causes wilt symptoms on Brassica horticulture crops. However, on oilseed rape V. longisporum does not induce wilting, but rather induces stem striping symptoms.Verticillium stem striping is an emerging disease in the UK as it was reported for the first time only in 2007, but is currently present in most regions in England. In Chapter 3, UK V. longisporum isolates were genotyped along with isolates from various countries in continental Europe, Japan and USA. UK isolates belong to the V. longisporum lineage that contains hybrids between the hitherto unfound Verticillium species A1 and species D1. Collectively, lineage A1/D1 consists of two populations; one that is abundant in Western Europe (including all UK samples) and one that is abundant more eastern in Europe. Both A1/D1 populations originate from the same hybridization event and diverged after hybridization for currently unknown reasons.In Chapter 4, the UK V. longisporum isolates were further characterized through pathogenicity tests under glasshouse conditions. The UK isolates were as virulent as previously characterized V. longisporum A1/D1 isolates on various Brassica hosts. However, as previously demonstrated, the virulence of A1/D1 isolates is distinct from V. longisporum strains from other hybridization events. Generally, the virulence was positively correlated with fungal colonization levels in the stem of infected plants.The impact of V. longisporum for UK oilseed rape production was assessed in Chapter 5, as hitherto a significant impact of Verticillium stem striping on yield was never demonstrated. The oilseed rape cultivars Incentive and Vision developed few symptoms upon V. longisporum challenge, whereas Harper and especially Quartz displayed abundant stem striping. The impact of V. longisporum on yield was variable over the two cropping years with one-year significant losses for all cultivars, whereas in the other year no significant losses were observed.V. longisporum emerged as a new pathogen through hybridization and colonized a host range that differs from the host range of other Verticillium pathogens. Chapter 6 describes the impact of hybridization as an evolutionary mechanism for filamentous microbes. New allele combinations with or without whole genome duplication upon hybridization can be invigorating for pathogens, leading to new disease emergences. Hybrid pathogens often developed distinct traits from their parents, such as an altered host range or higher virulence.The impact of hybridization on V. longisporum was further investigated in Chapter 7 by elucidating how these novel pathogenicity traits may evolve. V. longisporum received two complete chromosome sets from different Verticillium species that rearranged with each other. Consequently, V. longisporum genomes have a mosaic structure as chromosomes consist of sections of both parental origins. Furthermore, genes in V. longisporum generally have a higher diversification rate than the genes in haploid Verticillium spp., likely due to the presence of most genes in two copies. Hybridization also combined gene transcriptome patterns of two parental species leading to a novel transcription pattern in V. longisporum.As a side step, genome evolution of a notorious non-hybrid Verticillium pathogen, Verticillium dahliae, was studied. Previously, V. dahliae was suggested to evolve according to the two-speed genome model, as strains of this species carry lineage-specific regions that are hotspots for presence/absence polymorphisms, chromosomal rearrangements, active transposable elements and in planta-induced effector genes. Moreover, lineagespecific regions are enriched for segmental duplications. In Chapter 8 the sequence diversification of lineage-specific regions was investigated. Intriguingly, these regions display increased sequence conservation that affects both coding and non-coding regions. Such sequence conservation of accessory genome regions is an unprecedented finding in filamentous pathogens.Two-speed genome evolution in filamentous pathogens is further discussed in Chapter 9. Filamentous pathogens employ a variety of evolutionary mechanisms to generate genomic variation, especially in accessory genome regions. The diversity by which rapid evolution is achieved in filamentous pathogens to evade host immunity can be appointed to differences in lifestyle within this heterogeneous group of organisms.

ISBN: 9798708788030Subjects--Topical Terms:

1621997
Infections.

The Impact of Interspecific Hybridization on Fungal Plant Pathogens: A Case Study on the Emerging Pathogen Verticillium longisporum.
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However, on oilseed rape V. longisporum does not induce wilting, but rather induces stem striping symptoms.Verticillium stem striping is an emerging disease in the UK as it was reported for the first time only in 2007, but is currently present in most regions in England. In Chapter 3, UK V. longisporum isolates were genotyped along with isolates from various countries in continental Europe, Japan and USA. UK isolates belong to the V. longisporum lineage that contains hybrids between the hitherto unfound Verticillium species A1 and species D1. Collectively, lineage A1/D1 consists of two populations; one that is abundant in Western Europe (including all UK samples) and one that is abundant more eastern in Europe. Both A1/D1 populations originate from the same hybridization event and diverged after hybridization for currently unknown reasons.In Chapter 4, the UK V. longisporum isolates were further characterized through pathogenicity tests under glasshouse conditions. The UK isolates were as virulent as previously characterized V. longisporum A1/D1 isolates on various Brassica hosts. However, as previously demonstrated, the virulence of A1/D1 isolates is distinct from V. longisporum strains from other hybridization events. Generally, the virulence was positively correlated with fungal colonization levels in the stem of infected plants.The impact of V. longisporum for UK oilseed rape production was assessed in Chapter 5, as hitherto a significant impact of Verticillium stem striping on yield was never demonstrated. The oilseed rape cultivars Incentive and Vision developed few symptoms upon V. longisporum challenge, whereas Harper and especially Quartz displayed abundant stem striping. The impact of V. longisporum on yield was variable over the two cropping years with one-year significant losses for all cultivars, whereas in the other year no significant losses were observed.V. longisporum emerged as a new pathogen through hybridization and colonized a host range that differs from the host range of other Verticillium pathogens. Chapter 6 describes the impact of hybridization as an evolutionary mechanism for filamentous microbes. New allele combinations with or without whole genome duplication upon hybridization can be invigorating for pathogens, leading to new disease emergences. Hybrid pathogens often developed distinct traits from their parents, such as an altered host range or higher virulence.The impact of hybridization on V. longisporum was further investigated in Chapter 7 by elucidating how these novel pathogenicity traits may evolve. V. longisporum received two complete chromosome sets from different Verticillium species that rearranged with each other. Consequently, V. longisporum genomes have a mosaic structure as chromosomes consist of sections of both parental origins. Furthermore, genes in V. longisporum generally have a higher diversification rate than the genes in haploid Verticillium spp., likely due to the presence of most genes in two copies. Hybridization also combined gene transcriptome patterns of two parental species leading to a novel transcription pattern in V. longisporum.As a side step, genome evolution of a notorious non-hybrid Verticillium pathogen, Verticillium dahliae, was studied. Previously, V. dahliae was suggested to evolve according to the two-speed genome model, as strains of this species carry lineage-specific regions that are hotspots for presence/absence polymorphisms, chromosomal rearrangements, active transposable elements and in planta-induced effector genes. Moreover, lineagespecific regions are enriched for segmental duplications. In Chapter 8 the sequence diversification of lineage-specific regions was investigated. Intriguingly, these regions display increased sequence conservation that affects both coding and non-coding regions. Such sequence conservation of accessory genome regions is an unprecedented finding in filamentous pathogens.Two-speed genome evolution in filamentous pathogens is further discussed in Chapter 9. Filamentous pathogens employ a variety of evolutionary mechanisms to generate genomic variation, especially in accessory genome regions. The diversity by which rapid evolution is achieved in filamentous pathogens to evade host immunity can be appointed to differences in lifestyle within this heterogeneous group of organisms.
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