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ARS Home » Southeast Area » Charleston, South Carolina » Vegetable Research » Research » Publications at this Location » Publication #100851

Title: EVIDENCE FOR DOWNY MILDEW RACES IN CUCUMBER TESTED IN POLAND, INDIA, AND THE UNITED STATES

Author
item SHETTY, NISCHIT
item WEHNER, TODD
item Thomas, Claude
item DORUCHOWSKI, ROCH
item SHETTY, KP

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2002
Publication Date: 5/30/2002
Citation: N/A

Interpretive Summary: Downy mildew is an important fungal disease that attacks cucumbers worldwide. Cucumber varieties that are genetically resistant to downy mildew provide the most efficient and environmentally compatible method of controlling the disease. Resistant varieties have been developed in several countries including the U.S. However, it was not known if these varieties were resistant against different biological strains of the fungus that might be found in different geographical areas of the world. In this study, resistant varieties as well as advanced breeding lines of cucumber developed in China, Poland, and the U.S., were tested in India, Poland, and the U.S. to determine the effectiveness of their resistance against strains of the pathogen in other geographical areas. Strong differences were found in the resistance levels of some varieties when they were grown in other than the geographical area in which they had been developed, indicating that different races of the pathogen occur in the different areas included in the study. Therefore, the occurrence of these races must be given increased consideration in the development of resistant varieties. In this study, a variety from China and an advanced U.S. line developed at North Carolina State Univ. were the most resistant entries across all locations tested. These provide a useful starting point in development of varieties with resistance that will be effective against the different races of the pathogen that apparently occur in different areas of the world.

Technical Abstract: Downy mildew [Pseudoperonospora cubensis (Berk. and Curt.)] is an important disease in most cucumber (Cucumis sativus L.) production areas of the world. The objective of this experiment was to test a set of cucumber cultivars and breeding lines (hereafter referred to collectively as cultigens) which differed in their resistance to downy mildew to local isolates of P. cubensis in different geographical regions of the world, and to determine whether they differed in their resistance to the pathogen at those locations. Cucumber cultigens used in the study were developed in the U.S., Poland or China, and differed in their resistance to downy mildew. Cultigens were evaluated against local isolates of P. cubensis under field conditions (North Carolina and India) or greenhouse conditions (South Carolina and Poland). Significant differences were observed among cultigens for resistance to downy mildew at all locations. Individual cultigens differed in their resistance to the pathogen at different geographic locations providing evidence that the different local isolates represented different races of the pathogen. Cultigens from P.R. China that were resistant to downy mildew in that country were also resistant in India. However, those same cultigens were intermediate in resistance in the U.S. and Poland. Cultigens from the U.S. and Poland that were resistant in those countries were intermediate in resistance in India. The most resistant cultigens over all locations were 'Nongchen #3' (P.R. China) and M 21 (N.C. State Univ.).