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POSTERS: Pathogen detection, quantification and diagnosis

Application of Classical and Molecular Techniques for Screening Sweetpotato Germplasm Imported into the United States
Ronald French Monar - USDA-APHIS-PPQ-FO-Plant Germplasm Quarantine Program. Taylor Schulden- USDA-APHIS-PPQ-FO-Plant Germplasm Quarantine Program, Emma Sweeney- USDA-APHIS-PPQ-FO-Plant Germplasm Quarantine Program, Joseph Foster- USDA-APHIS-PPQ-FO-Plant Germplasm Quarantine Program, Pratyusha Bandla- USDA-APHIS-PPQ-FO-Plant Germp

Certain plant genera are known to carry pathogens not readily detected at inspection stations, such as viruses and viroids, and are restricted from entering the United States. The USDA-APHIS-PPQ-FO-Plant Germplasm Quarantine Program (PGQP) imports crops such as potatoes, sweetpotatoes, apples and sugarcane that belong to these prohibited genera. The Sweetpotato Program uses diagnostic tools, including PCR-based molecular testing and indicator plants, to identify such pathogens. Infected accessions must undergo tissue culture therapy prior to release. In 2018, 27 sweetpotato accessions were tested for viruses, including Geminiviruses, Potyviruses and Carlaviruses, using reverse transcription PCR (RT-PCR). Quantitative reverse transcription PCR (RT-qPCR) was used to screen for the West African and East African strains of Sweet potato chlorotic stunt virus. Seven accessions tested positive for a Potyvirus, although only two tested positive at the seedling stage. All seven accessions, when grafted onto the susceptible indicator plant Ipomoea setosa displayed symptoms, and the respective I. setosa tested positive for a Potyvirus by RT-PCR. The use of indicator plants complemented with molecular testing has proven critical in germplasm testing, and we are now beginning to implement high-throughput sequencing (HTS) technologies for diagnostics. Several positive controls for viruses of economic significance have now been sequenced, allowing for improved germplasm screening.