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Title: Polymorphic SSR markers for Plasmopara obducens (Peronosporaceae), the newly emergent downy mildew pathogen of Impatiens (Balsaminaceae)

item SALGADO, CATALINA - Rutgers University
item RIVERA, YAZMIN - Rutgers University
item VELTRI, DANIEL - Orise Fellow
item Crouch, Jo Anne

Submitted to: Applications in Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2015
Publication Date: 11/10/2015
Citation: Salgado, C.S., Rivera, Y., Veltri, D.P., Crouch, J.A. 2015. Polymorphic SSR markers for Plasmopara obducens (Peronosporaceae), the newly emergent downy mildew pathogen of Impatiens (Balsaminaceae). Applications in Plant Sciences. 3(11):1500073.

Interpretive Summary: Impatiens are one of the most popular of the summer flowering annuals, with sales ranked 1st among bedding plants in the U.S.A. In the past three years alone, impatiens growers have lost millions of dollars to a destructive new downy mildew disease, caused by a fungus-like pathogen, Plasmopara obducens. To understand the reasons why downy mildew is suddenly killing impatiens plants, we sequenced the genome of P. obducens, and used it to develop a set of DNA markers, capable of producing unique DNA fingerprints of the downy mildew pathogen. We identified over 13,000 of these DNA markers, and performed computer-based pre-screening to find a smaller subset possessing desirable qualities. A panel of 96 P. obducens samples collected since the onset of the downy mildew epidemic was screened using the 37 best DNA markers. We showed that just 17 of these new DNA markers provided sufficient information to fully differentiate the unique DNA signatures of the P. obducens samples. Scientists will use these new DNA markers to characterize the impatiens downy mildew pathogen, and track the origin(s) and progression of this destructive new disease.

Technical Abstract: Premise of the study: Microsatellite markers were developed for Plasmopara obducens, the causal agent of the newly emergent downy mildew disease of Impatiens walleriana. Methods and Results: A 151.2 Mb draft genome assembly was generated from P. obducens using Illumina technology and mined to identify 13,483 microsatellite motifs. Primers were synthesized for 62 marker candidates, of which 37 generated reliable PCR products. Testing of the 37 markers using 96 P. obducens samples showed 96% of the markers were polymorphic, with 2-6 alleles observed. Observed and expected heterozygosities ranged from 0.013-0.892 and 0.023-0.746, respectively. Just 17 markers were sufficient to identify all multilocus genotypes. Conclusions: This is the first set of microsatellite markers available for this pathogen, and one of the first molecular resources. These markers will be useful in assessing variation in pathogen populations and determining the factors contributing to the emergence of destructive downy mildew disease outbreaks in impatiens.