Development of a Greenhouse Screen for the Identification of Potato Mop-Top Virus and <i>Spongospora subterranea</i> Resistance in <i>Solanum tuberosum</i>

Potato mop-top virus and its protist vector, Spongospora subterranea, cause internal and external damage to potato tubers that make them unmarketable. Currently, there are no effective control methods to eliminate these soilborne and seedborne pathogens, so resistant germplasm is highly desired. A greenhouse assay was designed and validated to screen a large number of plants grown in both sandy soil and potting mix. High pathogen pressure was selected (20 sporosori/g of soil) to ensure successful inoculation, with an incubation time of 60 to 90 days. The successful use of conetainers was demonstrated to screen a large number of plants in limited greenhouse space. Thirteen susceptible commercial cultivars or breeding lines were screened in the greenhouse, with S. subterranea detected in 99.5% of the plants grown in both soil types. Potato mop-top virus was detected in 79.4% of the plants grown in 5-inch clay pots filled with sandy soil and 97.5% of the plants screened in conetainers filled with potting mix. The high pathogen levels detected in the 13 susceptible cultivars indicate that it is possible to assess potato germplasm resistance to S. subterranea and potato mop-top virus in the greenhouse. In the absence of a research field with consistently high pressure of S. subterranea and potato mop-top virus, this new greenhouse assay could rapidly identify germplasm with resistance to these two economically important pathogens year-round. Future identification of S. subterranea or potato mop-top virus-resistant germplasm will enable development of disease resistance markers that can help breeders rapidly identify resistant material. [Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2025.