HOST RESISTANCE

Natural Sources of Powdery Mildew Resistance in Arabidopsis

Luc Adam, Postdoctoral Fellow
Iain Wilson, Postdoctoral Fellow

In a collaborative project with Simon Ellwood, S. Xiao and J. Turner (University of East Anglia, Norwich, U.K.), 360 Arabidopsis accessions were screened for resistance or susceptibility to two species of powdery mildew, Erysiphe cruciferarum UEA1 and E. cichoracearum UCSC1 (Adam et al. 1999). A summary of this survey is given in Figure  1. A majority of accessions were susceptible to both powdery mildew isolates. Among the resistant accessions, 50 were strongly resistant to E. cichoracearum UCSC1, of which 38 were also strongly or moderately resistant to E. cruciferearum UEA1. Thus, there is significant natural diversity for powdery mildew resistance in Arabidopsis. In addition, it was confirmed that isolate UEA1 is a member of the species E. crucifereaum and the isolate UCSC1 is a member of the species E. cichoracearum (Adam and Somerville 1996).


Fig. 1. Summary of a survey of 360 Arabidopsis accessions for resistance to E. cichoracearum UCSC1 or E. cruciferearum UEA1. Accessions that were strongly or moderately resistant were grouped together and those that were strongly or moderately susceptible were grouped together in this analysis.


References:
  1. Adam, L., and S. Somerville. 1996. Genetic characterization of five powdery mildew disease resistance loci in Arabidopsis thaliana. Plant Journal 9: 341-356.
  2. Adam, L., S. Ellwood, I. Wilson, S. Xiao, G. Saenz, R. Oliver, J.G. Turner, and S. Somerville. 1999. Comparison of Erysiphe cichoracearum and E. cruciferarum and a survey of 360 Arabidopsis thaliana accessions for resistance to these two powdery mildew pathogens. Molecular Plant-Microbe Interactions 12:1031-1043.

Complex Inheritance of Powdery Mildew Resistance in Kashmir-1 and Warschau-1

Iain Wilson, Postdoctoral Fellow
Celine Schiff, Visiting Student
Douglas Hughes, Technian

Among the resistant accessions, Kashmir-1 (Kas-1) was one of the most strongly resistant to E. cichoracearum UCSC1. To determine the inheritance of resistance, Kas-1 was crossed to the susceptible Columbia-gl1. A set of F6 (Col-gl1 x Kas-1) recombinant inbred lines was established from this cross for mapping purposes. Initial results suggested that the inheritance was controlled by more than one gene and quantitative trait loci analysis (QTL) was used to provide an estimate of the number of resistance loci segregating in this cross. Three genes were identified: RPW10 on chromosome 3, RPW11 on chromosome 5 and RPW12 on chromosome 2 (Wilson et al. 2001). Of these genes, RPW10 had the strongest impact on the resistance phenotype, explaining 63% of the variation for this trait between the parent lines. Subsequently RPW10 was shown to be allelic to RPW8, a gene conferring resistance to a wide range of powdery mildews, including E. cruciferearum UEA1 and E. cichoracearum UCSC1 (Xiao et al. 2001).

The parent lines Kas-1 and Columbia-gl1 differ in a number of morphological attributes and in their vernalization requirement. The set of recombinant inbred lines can be used to study the inheritance of a range of traits in addition to powdery mildew disease resistance.

Table 1. Scores for the molecular markers for 129 F6 (Col-gl1 x Kas-1) recombinant inbred lines.

(Tab-delimited text file of Table) - can be imported directly into Excel if saved as a text file

(Downloadable Excel Spreadsheet) - works well with Internet Explorer, may have problems if using Netscape

Excel html file - best for on-screen viewing of the data . . . BUT WARNING, it may load slowly depending on your browser.

A second accession, Warschau-1 (Wa-1), was also highly resistant to E. cichoracearum UCSC1. In a parallel study, 94 F8 (Col-0 x Wa-1) were used to determine the inheritance of powdery mildew resistance. Two QTL designated RPW13 and RPW14 were identified (Schiff et al. 2001). The stronger locus, RPW13, was mapped to the bottom of chromosome 3 and was subsequently shown to be allelic to RPW8 and RPW10 (Xiao et al. 2001). RPW14 was placed on the upper arm of chromosome 1. The two loci, which act additively, explain 65% of the variation if disease resistance between Wa-1 and Col-0. Thus, four distinct powdery mildew resistance loci were identified in these two accessions.

Table 2. Scores for the molecular markers for 94 F6 (Col-0 x Wa-1) recombinant inbred lines.

Tab-delimited text file of Table) - can be imported directly into Excel if saved as a text file

(Downloadable Excel Spreadsheet) - works well with Internet Explorer, may have problems if using Netscape

(Excel html file) - best for on-screen viewing of the data . . . BUT WARNING, it may load slowly depending on your browser.


References:
  1. Schiff, C.L., I.W. Wilson and S.C. Somerville. 2001. Polygenic powdery mildew disease resistance in Arabidopsis thaliana. Quantitative trait analysis of the accession Warschau-1. Plant Pathology 50: 690-701.
  2. Wilson, I.W., C.L. Schiff, D.E. Hughes and S.C. Somerville. 2001. Quantitative trait loci analysis of powdery mildew disease resistance in the Arabidopsis thaliana accession Kashmir-1. Genetics 158: 1301-1309.
  3. Xiao, S., S. Ellwood, O. Calis, E. Patrick, T. Li, M. Colemen and J.G. Turner. 2001. Broad-spectrum resistance in Arabidopsis thaliana mediated by RPW8. Science 291: 118-120.