CLEANSEED: A PLANNING PROJECT TO ENSURE THE SUSTAINABILITY OF U.S. SWEETPOTATO SEED PROGRAMS.

This planning project will build capacity through collaborative relationships between clean plant centers, industry representatives, and multi-state teams of leading biological, physical, and social scientists to deliver efficient and effective solutions to issues confronting foundation seed used for commercial sweetpotato production. The goal of this planning project is to develop a large SCRI-SREP proposal that will address critical needs of the U.S. sweetpotato industry using stakeholder input to identify and prioritize research and educational objectives that will ensure a sustainable supply of high quality certified clean foundation seed (CCFS) in the future. All CCFS programs, which begin with virus-tested clean plant material, have experienced accelerated growth across the U.S. since sweetpotato joined the National Clean Plant Network (NCPN) in 2015. CCFS is important because sweetpotato plants are reproduced by vegetative propagation techniques and systemic pathogens, especially viruses, can accumulate in the propagation material and contribute to "cultivar decline", affecting yield, skin color, root shape and storage quality. Foundation seed programs are the sole source of planting material for commercial growers that is demonstrably clean, but unfortunately any sweetpotato can be used for propagation including those that have become re- infected during seed increase in the field as well as excess commercial stock that was never intended for use as seed. Therefore, it is important for growers to begin with foundation seed that is certified as clean seed by state crop improvement agencies. Since CCFS is the cornerstone of U.S. sweetpotato production, it is critical that we address several major problems that challenge the production, utilization, and sustainability of high-quality clean seed in the future.• We do not know how different propagation schemes, crop production practices, locations, or years affect the rate of re-infection and hence the quality and economic value of the seed. Although virus-tested clean seed have been shown to reduce cultivar decline, it has become evident that re-infection happens routinely in commercial operations. Currently, there are no data-driven recommendations on how to reduce re-infection.• Can we reduce the risks associated with using roots for seed by increasing the production of clean, certified plant material? Traditional sweetpotato propagation has relied on sprouting seed roots in field-beds to produce plant slips for transplanting in commercial production fields. The use of seed roots dramatically increases the risk of introducing soil-borne pathogens that can infect slips and compromise quality. In 2013, sweetpotato black rot caused by Ceratocystis fimbriata began to appear in NC and within two years it spread to other sweetpotato producing states. The highly destructive GRKN, Meloidogyne enterolobii was reported in NC during 2011 and SC by 2017. Sweetpotato producers across the U.S. purchase some seed from across state lines, which has provided the means for rapid distribution of black rot and GRKN to new areas. There are currently no efficacious or cost-effective management options once GRKN has entered a production system.• What is the quality of clean plant material currently provided to commercial growers, can this be improved, and how can we provide assurance of its quality? The risk of mutations in sweetpotato varieties has been reduced with micro-propagated clean plant material. However, epigenetic regulatory mechanisms may change based on frequency and type of micro-propagation techniques utilized in the lab and greenhouse. Epigenetic variations or mutations in sweetpotato cultivars may not be expressed until they enter commercial field production and may reduce crop yield and quality. In addition to recognizing how production practices affect incidence of mutations and re-infection by viruses, there is a need to objectively assess seed lots to determine the actual incidence of these problems and provide support for growers to make decisions on the quality of their seed and likely outcomes from its use. This will require characterizing previously unrecognized mutation/epigenetic effects, viruses, and developing specific assays for them and other pathogens such as M. enterolobii and C. fimbriata. Even for well recognized viruses, we have no systematic information to know if there are strain variations in viruses that affect our ability to detect them. Are there markers (e.g. virus incidence or molecular indicators of epigenetic effects, etc.) that could be used as indicators of seed quality? Filling these knowledge gaps will contribute to the sustainability of U.S. sweetpotato seed programs.• Anecdotal reports suggest that growers in different states have very different perceptions and attitudes regarding clean plants. There is a need to understand how growers select what they will use for seed, to provide scientifically sound information on seed quality and its economic value, to develop a strategic plan for the industry that will direct future research and extension efforts, and provide an approach to improving both the quantity and quality of clean plants.The long-term goal of this CleanSEED planning project will be to address the critical needs of the sweetpotato industry by identifying opportunities to leverage progress made by U.S. Clean Plant Centers to increase certified clean plant material across the nation. The planning project will identify stakeholders' priorities, gaps in knowledge, educational needs, and research areas that are needed to address these priorities. The planning project will then organize research teams to lead these efforts and develop a future SREP proposal that will address the barriers to clean plant accessibility and use, meet stakeholder priority needs, and enhance the sustainability and profitability of the sweetpotato industry.