Characterization of resistance genes to Cladosporium fulvum on the short arm of chromosome 1 of tomato

J. Haanstra

Research output: Thesisinternal PhD, WU

Abstract

<p>Plant breeders generally use qualitative resistance that is associated with a hypersensitive reaction (HR) to obtain cultivars that are resistant to pathogens and pests. The genetics of this resistance is based on the gene-for-gene relationship, which involves the product of a plant resistance gene and the product of an avirulence gene of the pathogen occurs. The interaction between leaf mold ( <em>Cladosporium fulvum</em> ) and its solely host, tomato ( <em>Lycopersicon esculentum</em> ), complies with this model. In the last few years, the isolation of several avirulence ( <em>Avr</em> ) and resistance ( <em>R</em> ) genes have contributed to an increase in our knowledge on this interaction. Several resistance genes to <em>C. fulvum</em> ( <em>Cf</em> genes) have been isolated from tomato. These <em>Cf</em> genes are located on two different clusters on the tomato genome, which contain not only functional <em>Cf</em> genes, but also several homologs with yet unknown function.. The short arm of Chromosome 1 harbors one of these clusters, designated "Milky Way", comprising functional <em>Cf</em> genes ( <em>Cf-4</em> , <em>Cf-4A</em> , <em>Cf-9</em> ). Moreover, two other clusters are located on the short arm of Chromosome 1, designated "Northern Lights" and "Southern Cross", which only harbor homologs ( <em>Hcr9</em> s), but no functional <em>Cf</em> genes. Also, there are several reports about the presence of other <em>Cf</em> genes on the short arm of Chromosome 1.</p><p>To increase our knowledge on the genetic and molecular organization of <em>Cf</em> genes on the short arm of Chromosome 1, an experimental approach was chosen to identify <em>Cf</em> genes with novel specificities that map on the short arm of Chromosome 1. To saturate the tomato genome with molecular markers, an integrated high-density AFLP-RFLP map was constructed using two different <em>L. esculentum</em> x <em>L. pennellii</em> F <sub>2</sub> mapping populations. Although 1175 AFLP markers were mapped on the tomato genome, covering 1482 cM, only nine AFLP markers were detected between the RFLP markers CT233 and TG51, which mark a 23.6 cM interval, comprising several <em>Hcr9</em> clusters, on the short arm of Chromosome 1. This relatively low number of markers is due to the clustering of most <em>Eco</em> RI/ <em>Mse</em> I AFLP markers around the centromeres (Chapter 2).</p><p>Testcross populations of 66 <em>C. fulvum</em> resistant <em>Lycopersicon</em> accessions were obtained by crossing these accessions with the near isogenic line Moneymaker-Cf4 and subsequent crossing of the F <sub>1</sub> with the susceptible tomato cultivar Moneymaker (Chapter 3). Using disease resistance tests with <em>C. fulvum</em> race 0 on only 24 plants of these testcross populations, susceptible plants were identified. An under-representation of susceptible plants identified <em>Cf</em> resistance linked to <em>Cf-4</em> , and hence location of the unknown resistance on the short arm of Chromosome 1. Out of the 21 resistant accessions that have been tested in this way, ten showed a <em>Cf-4</em> linked <em>Cf</em> gene. Among these ten accessions, one accession specifically recognized the extracellular protein ECP5 of <em>C. fulvum</em> and the corresponding gene was designated <em>Cf-ECP5</em> . This gene was more accurately mapped using a testcross population of 338 plants and an F <sub>2</sub> population of a cross between Moneymaker and CfECP5, consisting of 233 individuals. <em>Cf-ECP5</em> mapped 4 cM proximal to the <em>Hcr9</em> locus Milky Way and the corresponding <em>Cf</em> locus was designated Aurora. An amplification product that cosegregated completely with the <em>Cf-ECP5</em> gene, was cloned and nine clones were sequenced (Chapter 6). These nine clones could be classified into four groups, indicating that the Aurora locus comprises several <em>Hcr9</em> s.</p><p>Of the 66 resistant <em>Lycopersicon</em> accessions mentioned above, 64 have been screened for the presence of <em>Cf-4</em> and/or <em>Cf-9</em> , using PVX:: <em>Avr4</em> and PVX:: <em>Avr9</em> , respectively. A relatively large proportion of these accessions all harbored the functional genes <em>Cf-4</em> and <em>Cf-4A</em> (Chapter 4). Sequence analysis of the 3' end of <em>Cf-4</em> and part of the 3' untranslated region of <em>Cf-4</em> showed no differences from the previously published <em>Cf-4</em> sequences, hence these lines contain an introgression fragment with identical <em>Cf-4</em> and <em>Cf-4A</em> genes. Since several of these lines were previously designated with different <em>Cf</em> digits, a change in nomenclature is proposed.</p><p>Five out of the 66 accessions studied, showed an HR upon specific recognition of ECP2 and therefore harbor the corresponding resistance gene <em>Cf-ECP2</em> (Chapter 5). Using two different testcross populations and one F <sub>2</sub> population from a cross between Moneymaker and CfECP2, representing in total 282 individuals, <em>Cf-ECP2</em> was accurately mapped. <em>Cf-ECP2</em> cosegregates with the molecular marker CT116, which is located proximal to the Milky Way and Aurora clusters, but distal to the Southern Cross locus. Southern hybridization, using <em>Cf-9</em> as a probe, showed a hybridizing band of<img src="/wda/abstracts/ongeveer_enkel.gif"/>7.5 kb cosegregating with <em>Cf-ECP2</em> , indicating that <em>Cf-ECP2</em> is a member of a previously unidentified <em>Hcr9</em> locus, that has been designated Orion.</p><p>Studies in Chapters 3, 5 and 6 show that functional <em>Cf</em> genes can be located on several different <em>Hcr9</em> loci on the short arm of Chromosome 1 and that these <em>Hcr9</em> loci are highly polymorphic.</p>
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
Supervisors/Advisors
  • Stam, P., Promotor, External person
  • Lindhout, P., Promotor, External person
Award date4 Jan 2000
Place of PublicationS.l.
Print ISBNs9789058081421
Publication statusPublished - 2000

Keywords

  • tomatoes
  • solanum lycopersicum
  • passalora fulva
  • plant pathogenic fungi
  • disease resistance
  • pathogenicity
  • plant breeding

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