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Application of tissue culture to produce virus-free plants from imported potato germplasm

Ronald French-Monar: USDA-APHIS, Plant Germplasm Quarantine Program

<div>Certain plant genera are restricted from entering the United States because they are known to carry plant pathogens that are not readily detected at inspection stations, such as viruses and phytoplasmas. The USDA APHIS Plant Germplasm Quarantine Program (PGQP) imports apples, sugarcane, rice, stone fruit, potatoes, sweetpotatoes, and other crops belonging to these so-called “prohibited” genera. The Potato Quarantine Program uses a variety of diagnostic tools, including molecular and serological tests, indicator plants, and electron microscopy to detect pathogens that could threaten and compromise U.S. agriculture. Accessions that are found to be infected cannot be released and must undergo treatment in tissue culture. <em>In vitro</em> therapy procedures have allowed for the successful elimination of many pathogens, including viruses that are otherwise difficult to eradicate and would have made the germplasm unavailable to stakeholders. Between October 2016 and November 2017, the Potato Quarantine Program tested 117 accessions, including 27 that were previously found to be infected and had received therapy in tissue culture. Using a combination of heat therapy, chemotherapy, and meristem tip culture, pathogens were successfully eliminated from 26 accessions (96%). This included nine out of the ten accessions infected with <em>Potato Virus S </em>(PVS), all ten accessions infected with potyviruses, and all seven accessions infected with a combination of potyviruses, PVS, and/or <em>Potato Virus M</em> (PVM). The high rate of virus eradication achieved by using multiple <em>in vitro</em> therapy techniques, in combination, has allowed the program to release accessions that would otherwise have been unavailable for release.</div>