APS Abstract of Presentation

An integrative approach to characterizing the cucumber-Pseudoperonospora cubensis interaction
E. A. Savory (1), M. TIAN (1), C. Erhardt (1), M. Hausbeck (1), R. Hammerschmidt (1), B. Day (1)
(1) Department of Plant Pathology, Michigan State University, East Lansing, MI, USA
Phytopathology 98:S140

Downy mildew is an important disease of cucurbits (e.g., cucumbers, melons, etc.), caused by the obligate pathogen Pseudoperonospora cubensis. Historically, cucumber (Cucumis sativus) in the United States has been resistant to downy mildew. However, introduction of a potentially new pathotype of P. cubensis has caused devastating losses in recent years. Understanding the molecular and genetic interactions between host and pathogen during the infection process will enable us to elucidate the mechanisms of infection and disease progression and allow us to identify potential strategies for breeding downy mildew resistant cultivars. A three-fold approach has been undertaken to identify the genetic basis for enhanced virulence observed in recent field isolates of P. cubensis. First, phylogenetic characterization through the use of PCR and sequencing of P. cubensis isolates collected throughout the United States will be used to determine the genetic basis for enhanced virulence and to establish a genetic database. This database will allow us to monitor pathogen spread, disease occurrence and adaptation of P. cubensis with regard to host and environmental conditions. Second, suppressive subtractive hybridization (SSH) is being used to identify genes which are differentially expressed following infection with P. cubensis. These genes will be sequenced and their expression confirmed with RT-PCR and northern blots. Finally, the use of laser microdissection, will enable us to isolate single host cells at various stages of pathogen infection. These isolated cells will be used to profile gene expression during pathogen invasion. This integrative approach will provide aframework for determining the basis of pathogenicity and susceptibility in the P. cubensis-cucumber interaction which can be used to direct future management and breeding efforts.

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