Potato Diseases

There are many diseases of potato. The recently published 2nd edition of Compendium of Potato Diseases (APS Press) lists approximately 60 diseases caused by bacteria, fungi, nematodes, viruses, viroids, and phytoplasmas! Currently the PPG focuses primarily on three diseases of significance to Minnesota potato growers and potato growers worldwide, late blight, Verticillium wilt/early dying, and common scab.

Late Blight

Late blight is caused by the oomycete Phytophthora infestans. Under cool, humid conditions, the disease can cause severe foliar blight and infected tubers develop unsightly lesions in storage. Losses can be staggering: a seemingly healthy field can be entirely destroyed in as little as one week. Late blight was a major cause of the Irish Potato Famine of the mid-1800s during which an estimated 1 million people starved to death. Today, the disease remains a problem worldwide and ranks among the most important disease problems facing potato growers. Although climate conditions in Minnesota are not always conducive to late blight epidemic development, millions are spent each year on preventative chemical controls. The chemicals are costly for the growers and are potentially damaging to the environment.The PPG is seeking natural sources of durable late blight resistance. Many wild potato species are reported to carry resistance. We are systematically screening wild materials in search of new and robust resistance genes. We are also conduct molecular and genetic studies on these materials to characterize, map, and isolate the genes. Using non-transgenic methods including somatic hybridization and embryo rescue, we will transfer promising genes into a potato background and release materials for use by potato breeding programs. In addition to our work with wild species, we assist potato breeders throughout the country by field screening breeding lines for resistance to late blight through collaborations with breeders at UM and at the University of Wisconsin, and by serving as a testing site for the National Late Blight and Quad-State (MI, MN, ND, WI) tests. In the lab, we are evaluating protocols for detached leaf and tuber assays. Finally, our genomics program seeks new and efficient means for identifying and isolating potentially useful late blight resistance genes. Current projects include development of methods to identify genes up-regulated in response to late blight attack and allelic mining methods for known late blight resistance loci.

The soil-borne pathogens Verticillium dahliae and V. albo-atrum are widespread potato pests and can cause severe yield and quality losses. The pathogens attack the vascular tissues, resulting in a characteristic wilted phenotype. An infected field is yellow or brown with infected plant stems remaining upright. The root-lesion nematode Pratylenchus penetrans can increase the incidence and severity of V. dahliae infection, an interaction known as early dying syndrome. Genetic plant resistance is among the most promising and effective means of controlling losses due to Verticillium. The PPG maintains two Verticillium nurseries for germplasm screening. The first, located at the Northern Plains Potato Growers Association Research Farm in Grand Forks, ND, is infested with high levels of both V. dahliae and V. albo-atrum. The second nursery, at the UM North Central Research and Outreach Center in Grand Rapids, MN, is infested with V. dahliae and P. penetrans, allowing for accurate tests for early dying resistance. In these nurseries we screen breeding materials from the UM Potato Breeding Program and breeding programs at Michigan State University, University of North Dakota, and University of Wisconsin. We also screen mapping populations and other research materials. Beginning in 2002, at our early dying nursery in Grand Rapids, MN, we are also screening wild potato species. These species are the building blocks of our efforts to incorporate genetic resistance for longterm potato protection. Genes of particular promise will be mapped and isolated using molecular and genomics tools. Non-transgenic methods will be used to introduce important genes into a potato background.

Common Scab

True to its name common scab, caused by Streptomyces spp., is a bacterial disease common to potato growing areas throughout the world. Although the pathogen does not significantly reduce plant vigor or crop yield, the characteristic tuber lesions greatly reduce tuber quality. Symptoms may range from mild to deep, severe lesions known as pit scab. Cultural practices, including planting clean seed, long crop rotation periods, and maintaining lower soil pH levels are among the recommended methods of disease management. Although there is variation in susceptibility amongst potato cultivars, none is thought to be immune. At our common scab nursery in Becker, MN, the PPG assists breeders at UM and other universities by evaluating potato breeding lines for resistance to common scab. We are a test site for the National Scab trial. We also test research materials including somatic hybrids derived from potato + wild potato species and mapping populations derived from somatic hybrids.