Evidence of Rapid Infection of Four Sweetpotato Potyviruses in a Commercial Field in California

Sweetpotato (Ipomoea batatas Lam.) is grown worldwide and is a staple food in many countries. One of the main constraints for sweetpotato production is cultivar decline, caused by the accumulation of viruses and subsequent losses of storage root yield and quality over years of vegetative propagation. Virus indexing using diagnostic molecular techniques is essential for the detection and identification of the major viruses to avoid cultivar decline, but little information is available on the fate of clean (virus-tested) plant materials after field propagation. In this study, cuttings of three sweetpotato cultivars (Beauregard, Bellevue, and Vermillion) were acquired from a clean propagative material program and planted in commercial field plots in Merced County, California, over multiple growing seasons. In 2021 and 2022, the phytosanitary status of storage roots from different generations of the materials were assessed by reverse transcription quantitative PCR (RT-qPCR) at harvest at the Foundation Plant Services, University of California, Davis. The results showed their rapid infection with four major potyviruses-sweet potato feathery mottle virus, sweet potato virus 2, sweet potato virus C, and sweet potato virus G-over the two seasons. The infection by two to four potyviruses was confirmed by RT-PCR, RT-qPCR, high-throughput sequencing, and biological indexing onto Ipomoea setosa plants for symptoms evaluation.