The front line of any potato production system is high-quality, productive seed from a high-performing cultivar. Defective, unproductive seed leads to a low stand that not only directly compromises the yield and quality of the crop, but also lowers the efficiency and cost-effectiveness of the nutrient and pest management programs. Seed health and productivity is determined by physiological condition and disease prevalence.
Buying certified seed and inspecting seed lots for internal and external issues before acceptance are necessary to obtain healthy, productive seed. In addition, maintaining a good relationship with seed suppliers is important. If possible, growers should visit the site of production to observe field and storage conditions of their seed stock. Information to request from seed suppliers includes: certified seed certificate, size and grade, cutting preference, shipping details, and any potential field problems that occurred during the production season.
Physiological condition of seed tubers is influenced by proper handling and storage. Growing season stress, storage temperature and time, as well as loading/unloading, transport, and cutting all provide opportunity for bruising, wounding, splitting, cold injury, and other physiological conditions to ensue. Potatoes bruise easily and a six-inch drop or higher should be avoided. Bruises, wounds, and splits serve as pathogen entry points. Diseases caused by wound-entering pathogens include early blight and Fusarium dry rot.
All cultivars are susceptible to these storage pathogens, so warm environments should be avoided with wounded potatoes. The wound healing stage is critical in tuber storage. A wound healing environment has a high relative humidity (90% to 95%), is well ventilated, and maintains a temperature range of 45°F to 50°F.
When cutting seed pieces, keep cutting implements disinfected to avoid pathogen transfer, and sharp to avoid tearing damage. Low oxygen storage environments can cause increased tuber aging and reduced germination. Low oxygen also leads to excessive moisture environment that can cause enlarged lenticels and increased susceptibility to bacterial soft rot pathogens. Maintaining proper temperature is critical, as heating speeds tuber aging, and temperatures less than 38°F can cause cold injury that reduces germination and favors bacterial soft rot development.
Fungal and bacterial pathogens, as well as viruses and nematodes, all can all affect the quality of seed potatoes. Diseased seed can lower plant vigor and supply inoculum for further infection throughout the growing season. Late blight, scurf, scab, bacterial ring rot, black dot, and bacterial soft rot have been the seedborne diseases that are traditionally problematic. However, recent concerns have been with a new bacterial disease in the U.S., caused by Dickeya dianthicola. Dickeya is an aggressive pathogen that has devastated potato crops in the mid-Atlantic region, and has recently been detected in Pennsylvania, Maryland, Virginia, North Carolina, West Virginia, and Florida on potato seed stock sourced from Maine and Canada. Potato growers throughout the U.S. are on high alert and should monitor seed stock for Dickeya and other seedborne diseases.
Obtaining certified seed stock with a guaranteed low incidence of disease should be the first step of any potato management program. Most seed producers in the U.S. have a seed certification program that provides a North American Certified Seed Potato Health Certificate to buyers. Certification programs produce high-quality seed stock; however, all pathogens cannot be eliminated entirely, so suppression is key. The goal of certification programs is to minimize yield losses and pathogens spread due to disease.
Certified seed stock shipments should be inspected and evaluated before accepting them. Visual inspections should be performed carefully, examining the seed closely for both external and internal symptoms. External bruises, wounds, and splits can indicate storage pathogen entry points. Seed also should be cut to inspect for internal symptoms, such as discoloration and rot, because sometimes these symptoms are not visible from the outside. Avoid planting symptomatic seed or use a seed treatment as necessary.
Contact your local Extension office with questions about seed stock and for diagnostic help. Planting certified seed is only the first step to reducing seedborne diseases, and other integrated pest management strategies such as seed treatments and in-season disease monitoring also should be implemented to guarantee a productive potato crop.