ARS | Publication request: Pathogenic variability of individuals and populations of cucurbit powdery mildew–great confusion and great mystery, or why we still need the classical phytopathology.

Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: July 30, 2009
Publication Date: September 2, 2009
Citation: Lebeda, A., E. Krístková, B. Sedláková, J.D. McCreight, and M.D. Coffey. 2009. Pathogenic variability of individuals and populations of cucurbit powdery mildew–great confusion and great mystery, or why we still need the classical phytopathology, p.8. In: I. Šafránková, Šefrová, H. (Eds.) (ed.). XVIII. Ceská a slovenská konference o ochrane rostlin. Sborník abstraktu (XVIII. Czech and Slovak Plant Protection Conference. Proceedings of Abstracts). Mendelova zemedelská a lesnická univerzita v Brne (Mendel Agriculture and Forestry University in Brno), 2.-4. zárí 2009 (2.-4. September 2010), p. 8. (ISBN 978-80-7375-316-0), Brno (Czech Republic).

Technical Abstract: Golovinomyces cichoracearum and Podosphaera xanthii (family Erysiphales) are considered the most important species causing cucurbit powdery mildew (CPM), a serious disease of field and greenhouse cucurbits. Podosphaera xanthii (Px) is common in subtropical and tropical areas and in greenhouses in temperate areas, while G. cichoracearum (Gc) occurs more frequently in fields in temperate and colder areas. Both species may occur singly or together on cucurbits in Central Europe. Cucurbit isolates of Gc and Px differentially cross-infect all cucurbit species and genera and may be characterized as pathotypes. Populations of CPM vary spatially and temporally. Breeding of cucurbits for resistance to CPM is hindered by the lack of clear and uniform descriptions of the genetic variation in the pathogenicity of the CPM pathogens and genetics of resistance in the cucurbits. Various, independent systems of pathotype and race determinations and denominations of CPM pathotypes and races are in use worldwide, and there is no international cooperation or agreement in those topics. In this paper we critically review the current state of understanding of variation for pathogenicity of these two CPM pathogens at the pathotype and race levels, and propose for use by the international CPM research, breeding, seed and production communities: 1) two sets of differential cucurbit genotypes for the identification of CPM pathotypes and races, respectively, and 2) an objective, efficient, uniform, comprehensive coded system for meaningful, concise designation of CPM pathotypes (sextet code) and races (septet code). The proposed set of pathotype differentials includes six genotypes of three genera (Cucumis, Cucurbita, Citrullus). The proposed the set of CPM race differentials includes 21 genotypes of a single species, Cucumis melo L. This study clearly demonstrates that in the age of molecular biology we are still missing the basic information of “classical phytopathology,” i.e., about variation of the host-pathogen interactions from the viewpoint of host range, pathogenicity variation on different genotypes of one host species, including their precise specification and denomination. These basic data are the background for further detailed and internationally accepted studies of CPM pathogenicity variation on individual and population levels, as well as their understanding on genetical and molecular levels.