Submitted to: Journal of Plant Diseases and Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/11/2003
Publication Date: 9/8/2003
Citation: Lebeda, A., Widrlechner, M.P. 2003. Development of an improved set of cucurbitaceae genotypes for differentiation of pseudoperonospora cubensis pathotypes. Journal of Plant Diseases and Protection. v.110. p. 337-349. Interpretive Summary: Cucurbit downy mildew is a serious disease of melons, cucumbers, squash and related species. The disease organism (pathogen) is characterized by large variation in the damage it can cause and in specificity to particular host plants. This review summarizes our current state of knowledge about interactions between cucurbit downy mildew and its host plants, the genetics of host reactions, and overall variation within the pathogen. To date, only a preliminary set of cucurbit varieties had been designated to help distinguish among different races of cucurbit downy mildew. In this paper, we propose an improved set of cucurbit varieties to characterize variation in the pathogen. The proposed set includes 12 types representing six different genera, which are all natural host plants for the disease, and basic information on host-parasite specificity and variation is available. These varieties are accurately identified and available as genebank accessions. Our proposed set can serve as an appropriate baseline for more detailed research and communication of relationships between cucurbit downy mildew and its hosts. Steps to foster international collaboration on these topics are suggested and discussed.
Technical Abstract: Cucurbit downy mildew (Pseudoperonospora cubensis) is characterized by large variation in pathogenicity, specificity and host-parasite interactions. This report reviews the current state of understanding regarding interactions between P. cubensis and Cucurbitaceae, the genetic control of host reactions, and overall variation within the pathogen. A well-characterized set of differential Cucurbitaceae genotypes for the identification of P. cubensis pathotypes or races has not yet been designated. A preliminary set designated by Thomas et al. (1987) was, in certain cases, deficient in taxonomic description, precise characterization of the genotypes at the level of accession, uniformity of differential response, and international availability. An improved differential set of cucurbit accessions for characterization of pathogenic variability of P. cubensis isolates is proposed in this paper. The proposed set includes 12 genotypes from six genera (Benincasa, Citrullus, Cucumis, Cucurbita, Lagenaria and Luffa). These differentials are natural host plants of P. cubensis, and basic information on their host-parasite specificity and variability is available. The members of this new set are taxonomically characterized and available as genebank accessions. The data about host genera and pathogen variation summarized here fully support previous reports about the existence of distinct physiological forms (pathotypes and races) of P. cubensis, and a tetrade coding system is offered to designate P. cubensis pathotypes. This paper presents evidence that such forms may be delimited based on host genus, species and intraspecific specificities. This proposed differential set of Cucurbitaceae should serve as an appropriate baseline for more detailed research of P. cubensis isolate variation and population structure at the level of pathotype. Steps to foster international collaboration on this topic are suggested and discussed.