Submitted to: American Journal of Potato Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/25/2006
Publication Date: 5/1/2007
Citation: Pfaff, K., Jansky, S.H. 2007. Effect of time and storage temperature on survival of Verticillium dahliae microsclerotia in dried potato stem tissue. American Journal of Potato Research. 84:271-273. Interpretive Summary: Verticillium wilt is a serious disease of potato caused by a soilborne fungal pathogen. The most promising control method is the development of resistant cultivars. In order to identify resistant plants, breeders can grow them on infested soil and then collect stems, dry them, plate them on selective media, and count the number of fungal colonies that grow. Resistant plants will have few colony forming units in their stems. It is often difficult for a breeder to find time to process all stems immediately after they are collected. Therefore, it is important to know how long the stems can be stored before pathogen viability declines significantly. In addition, the breeder should know what storage environment is best for maintaining pathogen viability in stored stems. This research project studied the ability to detect the fungal pathogen in dried potato stems stored over time and at four temperatures (-80C, -20C, 4C, 23C). Pathogen levels decreased slowly for the first six months and then more quickly after that. A refrigerator (4 C) works best for long-term storage. Long-term survival of microsclerotia was lowest in samples stored at room temperature. These data indicate that stem samples can be stored for processing for several months. If processing is to occur after that, then samples should be stored in a refrigerator.
Technical Abstract: Verticillium wilt (Vw) is a widespread and significant disease of potato (Solanum tuberosum). It is caused mainly by the soil-borne fungi Verticillium dahliae and V. albo-atrum. Host plant resistance is a promising method of Vw control. Culture-based methods that quantify the pathogen in host stem tissue are often used for Vw resistance screening. Either stem sap or dried stem tissue can be plated to measure pathogen populations in stems of plants that have been exposed to the pathogen. This study evaluated the effect of storage time and temperature on the survival of V. dahliae microsclerotia in dried stem tissue. In both years of the study, the number of colony forming units (cfu) in stem samples did not change dramatically for the first six months in storage, regardless of storage temperature (-80C, -20C, 4C, 23C). After that, cfu means decreased sharply at all temperatures. Long-term survival of microsclerotia was lowest in samples stored at room temperature. These data indicate that stem samples can be stored for processing for several months. If processing is to occur after that, then samples should be stored in a refrigerator.