Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: March 15, 2005
Publication Date: March 15, 2005
Citation: Chen, J., Gulya Jr, T.J., Vick, B.A., Hu, J. 2005. TRAP analysis of molecular variability of a global collection of sunflower downy mildew, Plasmopara halstedii. Sunflower Research Workshop Proceedings. 27th Sunflower Research Workshop, January 12-13, 2005, Fargo, ND. Available: http://www.sunflowernsa.com/research/research-workshop/documents/Chen_TrapAnalysis_05.PDF Interpretive Summary: The fungal pathogen, Plasmopara halstedii, is the causal agent of sunflower downy mildew, a potentially devastating disease. Understanding the molecular variability of P. halstedii throughout the world will help devise strategies for controlling this disease. Two previous studies with random amplification of polymorphic DNA (RAPD) and simple sequence repeat (SSR) have revealed low level of genetic variability among isolates of different pathogenicity and geographical origins. This study employed the target region amplification polymorphism (TRAP) marker technique to analyze the molecular variability of a representative sample set of 92 isolates from 12 countries and belonging to 24 different races. The fixed primers were designed against 29 downy mildew EST (expressed sequence tag) sequences in the GenBank database (http://www.ncbi.nlm.nih.gov). About 2000 fragments were amplified and only 87 (4.4%) markers were polymorphic. These 87 markers discriminated each of the 92 isolates but none of them was tightly associated with physiological races, nor the origins.
Technical Abstract: The biotrophic pathogen Plasmopara halstedii causes a potentially devastating disease of sunflower (Helianthus annuus L.), downy mildew. Understanding the molecular variability of P. halstedii throughout the world will help devise strategies for controlling this disease. This paper reports the results of analyzing the genetic variability of 92 isolates of P. halstedii collected from 12 countries by using the target region amplification polymorphism (TRAP) marker technique. Pathogenicity tests classified these 92 isolates into 24 different races. Eighty-six polymorphic TRAP markers were amplified with fixed primers derived from known P. halstedii DNA sequences in combination with arbitrary primers. These 86 markers discriminated each of the 92 isolates, but none of the markers were tightly associated with pathogenicity races, nor with geographic origins. Cluster analysis based on genetic distances grouped these 92 isolates into roughly eight groups. Group III contained 15 isolates, of which 13 were collected in the USA. Twelve of these U.S. isolates were races 700s or 7000s. Three of six isolates of race 1000 were placed in Group VIII alone with the only isolate of race 100. The remaining six groups consisted of isolates of different races and origins.