Submitted to: Advances in Downy Mildew Research
Publication Type: Proceedings
Publication Acceptance Date: 7/10/2007
Publication Date: 9/1/2007
Citation: Lebeda, A., Stepankova, J., Krskova, M., Widrlechner, M.P. 2007. Resistance in Cucumis melo germplasm to Pseudoperonospora cubensis pathotypes. Advances in Downy Mildew Research. 3:157-167. Interpretive Summary: nteractions between melon (Cucumis melo) plants and the serious disease organism, downy mildew (Pseudoperonospora cubensis) show a wide range of severity and specificity. We investigated these inteactions by screening of 52 melon germplasm accessions with 8 different isolates of downy mildew. The isolates varied in disease response when tested on a broad range of potential host plants. The reactions of the melon accessions were evaluated on discs taken from the leaves. The intensity of mildew spore production was measured 6 to 14 days after inoculation. We observed relatively little variation in reaction patterns. Most melon accessions were highly susceptible. Altogether, 39 melon accessions showed susceptibility to all 8 isolates. Relatively few accessions expressed incomplete resistance (8 accessions in 15 interactions) or heterogenous reactions (8 accessions in 13 interactions), where some plants in an accession were susceptible but others were resistant. Only one melon accession from India (PI 315410) was found to be highly resistant to 7 of 8 mildew isolates. Among the 52 melon accessions, 14 different reaction patterns could be distinguished based on qualitative differences in disease response. These results are useful to both plant pathologists and breeders, as we seek to understand the nature of downy mildew resistance and to develop more tolerant cultivars, which in turn can reduce pesticide use.
Technical Abstract: The Cucumis melo-Pseudoperonospora cubensis host-pathogen interaction is characterized by large variation in specificity. This report summarizes results obtained by laboratory screening of 52 C. melo accessions by 8 isolates of P. cubensis. The isolates represent 8 different pathotypes with low, medium or high levels of pathogenicity. The reaction of C. melo accessions was evaluated on leaf discs removed from adult plants; sporulation intensity of P. cubensis isolates was measured 6 to 14 days after inoculation. Relatively little variability in reaction patterns to P. cubensis isolates was detected. The majority of C. melo accessions was highly susceptible to most of the P. cubensis isolates studied. Altogether, 39 C. melo accessions showed susceptibility to all 8 isolates. Relatively few accessions expressed incomplete resistance (8 accessions in 15 interactions with P. cubensis isolates) or heterogenous reactions (8 accessions in 13 interactions). Only one accession (PI 315410) was found to be highly resistant to some P. cubensis isolates. Among studied C. melo accessions, 14 different reaction patterns can be distinguished based on qualitative differences in response to this set of P. cubensis isolates.