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Development of a rapid molecular assay for the Ug99 race group of Puccinia graminis.
L. J. SZABO (1). (1) USDA-ARS, St. Paul, MN, U.S.A.

In the last decade a new group of highly virulent races of the wheat stem rust pathogen, <i>Puccinia graminis</i> f. sp. <i>tritici</i>, has caused epidemics in Northeast Africa and is a threat to wheat production worldwide. This race group (Ug99 RG) currently contains seven distinct members. A two-stage molecular diagnostic assay was developed using real-time polymerase chain reaction methodologies and fluorophore-labeled hydrolysis probes. Stage 1 uses a suite of four assays to identify samples belonging to the Ug99 RG. An internal control, based on the actin gene, is included to reduce false negatives. Only Ug99 RG samples are positive for all four of the assays. The stage 2 assay uses a suite of eight allele-specific SNP markers to predict the specific race phenotype of the sample within the Ug99 RG. A worldwide collection of over 400 samples has been used to validate this assay system. The assay performed reliably with a range of samples including pure fungal spores, infected plant tissue and ethanol-treated infected wheat stem tissue. This assay system provides a rapid and accurate method for diagnosis of Ug99 RG and will allow pathologists to monitor the movement this economically important group of races of the wheat stem rust fungus.<p><p>Keywords: Fungus, Cereals-Grains, Wheat

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