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Race-specificity in interactions between Cucumis melo germplasm and Pseudoperonospora cubensis

Lebeda, A., Kristkova, E., Sedlakova, B., Stepankova, J., Widrlechner, M. P.
Acta horticulturae 2017 no.1151 pp. 203-210
Cucumis melo, Pseudoperonospora cubensis, USDA, downy mildew, germplasm, host-pathogen relationships, introduced plants, muskmelons, pathotypes, plant pathogens, races, screening, Czech Republic, France, Iowa
Pseudoperonospora cubensis, the causal agent of cucurbit downy mildew, is one of the most economically important plant pathogens. Muskmelon (Cucumis melo) is seriously affected by P. cubensis. Within C. melo, several genotypes resistant to P. cubensis have been described; however, we lack detailed experimental studies focused on deciphering variation in this host-pathogen interaction. This study aims to describe race-specific variation in interactions between C. melo germplasm and isolates of P. cubensis. Under controlled inoculation, 52 accessions of C. melo were studied for resistance/susceptibility to 8 isolates of P. cubensis. The plant material was obtained from the USDA Plant Introduction Station, Ames, Iowa, USA. Pathogen isolates originated from the Czech Republic (7 isolates) and France (1 isolate) and represented 8 distinct pathotypes as determined following Lebeda and Widrlechner (2003). Collectively, 8 different race-specific reaction patterns were recorded. Most C. melo accessions (in total, 39) were highly susceptible to all isolates. None of screened C. melo accessions expressed complete resistance to all isolates. Only accession PI 315410 (VIR 5682) was found to be resistant to 7 of the 8 P. cubensis isolates. The study confirmed the race-specificity of interactions between C. melo and P. cubensis and established a sound framework for the development of a system to determine and classify P. cubensis races, which, in turn, should foster further broad screening of C. melo germplasm with a likelihood of detecting more effective sources of resistance to important pathotypes and races of P. cubensis.