Student Focused. The cause is Streptomyces scabies which resembles a bacterium but produces a mycelium, like a fungus. The flesh of the potato is not usually affected and after cooking the scab pulls away with the skin. I get multiple calls each year about common scab and what can be done to control this disease. 3 Replies 1072 Views July 26, 2012, 16:31 by fatcat1955 : Storing my potatoes … The NDSU Plant Diagnostic laboratory can test for scab types for a nominal fee. Current research by Dr. Linda Kinkel in Minnesota has found local soil microbial populations have reduced common scab. For information about UMaine Extension programs and resources, visit extension.umaine.edu. Diagram. This all too common problem is generally referred to as common scab. Soil ph measured 7.6 and I have learned since last year that potatoes like acid soil...the reason, most likely, for the scabby potatoes. The most widely distributed pathogen in the genus is Streptomyces scabies. Planting scab-resistant potatoes can be one of the best options, if the cultivar fits the potato operation. Cause of Potato Scab. Dry soil conditions during this period reduce competition and can serve to encourage infection by the pathogens. Thin-skinned potato varieties tend to be more severely affected. Another name for it may be ‘Common scab’, as there are other scabs, like ‘Acid scab’ caused by Streptomyces acidiscabies, that are found on potatoes but have much more limited distributions. However, its appearance is undesirable and decreases the quality and value of the potato. Infected seed serves to distribute the pathogen. It may increase common scab when soil pH increases. Small, rough, reddish or brown corky lesions form on the skin of the tuber. Potato Common Scab. Tubers of standard white and red varieties generally are round to oblong and relatively thin skinned compared to russets. Initially, infections appear as small tan to reddish-brown spots on the tuber surface. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied. Potato scab is a common and disfiguring disease of potato tubers that affects potatoes wherever they are grown. of iron sulfate /1,000 sq. Land Grant. Common scab of potato is caused by three species of Streptomyces: S. scabies, S. acidiscabies, and S. turgidiscabies. Russetted varieties tend to be less affected than smooth-skinned varieties. It can be difficult to visually determine the difference between common scab and powdery scab. As the potato plant cells die, they produce cork cells that push outward and form a scab lesion. Sometimes just a few but in a bad case they cover the the skin. Potato scab is caused by a soil bacterium. Find more of our publications and books at extensionpubs.umext.maine.edu. Increased interest in new gourmet varieties has added purple, blue, orange, yellow, and other colors to the inventory. Streptomyces acidiscabies is able to cause disease at a lower soil pH than that of Streptomyces scabies. For information about UMaine Extension programs and resources, visit extension.umaine.edu. Plant in well-drained soils and lower the soil pH to 5.5-6.0 where scab is a problem (apply 14 lbs. Potato scab is a bacterial disease that causes unsightly lesions, pitting or depressions on potatoes. However, there is less information available about susceptibility of tubers to the infection and development of common scab during late season tuber bulking. Symptoms of powdery scab include small lesions in the early stages of the disease, progressing to raised pustules containing a powdery mass. Saving your own seed potatoes is generally not worthwhile because viruses and diseases often show up the next year. of elemental sulfur and shake to thoroughly coat prior to planting. Increased populations of the pathogens can occur with repeated plantings of susceptible crops. Once in the plant, Streptomyces scabies produces a phytotoxin called thaxtomin that breaks down cell walls and penetrates rapidly growing cells. Common scab of potato, which has a worldwide distribution, is caused by filamentous bacteria in the genus Streptomyces. Early infection can lead to deeper scab lesions on the tuber. A laboratory analysis is always a good idea to get the correct diagnosis. Remove all plant material at the end of the potato harvest. Streptomyces spp. University of Maine, 5741 Libby Hall, Room 103, 4-H Camp & Learning Center at Bryant Pond, 4-H Camp & Learning Center at Greenland Point, 4-H Camp & Learning Centers at Tanglewood & Blueberry Cove, Insect Pests, Plant Diseases & Pesticide Safety, Affiliated Programs, Partners & Resources, Non-Discrimination Statement & Disability Resources, Register for Workshops, Classes, & Events. can survive in the soil as saprophytes. Common scab has been suppressed by pentachloronitrobenzene (Blocker) as an in-furrow soil treatment. Powdery scab was first found in Germany in 1841 and spread throughout Europe by 1855. Gretchen Voyle. It is transmitted to plants by infected seed tubers, wind and water. Plant potatoes in late winter (see planting chart). The bacterium from Streptomyces species is spread by spores on seed, in the soil, in soil water and can hitch a ride on nematodes or insects. It is going to take an ongoing effort of research, breeding and better management practices to decrease common scab severity. Potato scab lesions on tubers can be quite variable but generally appear as rough, corky lesions, which may range from small and raised to deeply pitted. You can add a comment by filling out the form below. This potato blemish causes unwanted ugly, scabby lesions that spoil the appearance of the tuber and make them undesirable to consumers or difficult to process. Mature symptoms appear as round, slightly raised and usually shallow lesions (1/16 to 1/4 inch in diameter), which may show raised margins (Figure 2B). Use seed pieces that have at least one good eye and are about the size of 1- to 2-inch cubes. Potato scab control is targeted at preventing infection in potatoes; once your potatoes are covered in scab, it’s too late to treat. Neither the pathogens nor the disease develops on tubers in storage. Streptomyces turgidiscabies also may be present and contribute lesions. On tubers, initial powdery scab symptoms appear as purplish-brown lesions that later develop into small blisters occurring as early as 43 days after planting (Figure 2A). Purchase only certified seed tubers for planting to help reduce disease problems. It is a member of the … The type of scab (raised, superficial or pitted) varies based on the potato cultivar, environment and soil microbial community. The pathogen is widespread and occurs in most potato-producing areas of the world. Future potato beds can be protected from scab by keeping the soil pH of beds around 5.2 with liberal applications of sulphur. Potato scab is a production problem that affects grade quality but has only a negligible effect on total yield or storability. You may see the following symptoms: Common scab: Raised, rough patches of skin on the tuber surface; Powdery scab: Irregular brown raised areas or depressions, often with papery margins, on the surface of tubers. Life-cycle of powdery scab, Spongospora subterranea. In general, scab tends to be worse in drier, lighter soils and those high in organic matter. Until recently, the disease has been considered rare and … As we all start thinking about the 2018 crop, I hope this article will help us all understand common scab better. Potato is a cool-season vegetable that ranks with wheat and rice as one of the most important staple crops in the human diet around the world. This genus is diverse and abundant in most soils of the world. Rotation with nonhosts will reduce but not eliminate the pathogen. This wide spread disease expresses itself as raised, superficial and/or pitted lesions on the tuber (Figure 1 and 2). Issued in furtherance of MSU Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Chemical management for common scab would likely include a good seed treatment to help maintain good plant health. Plain text formatting. Close-up of Photo 1: potato tuber with symptoms of powdery scab, Spongospora subterranea. Photo 3. For this article, I wanted to summarize the biology of common scab and discuss what research has found to reduce common scab on potatoes. Use acidifying fertilizers; use gypsum rather than lime. A recent study reported that fludioxonil (Maxium) reduced common scab by 58% and a biopesticide containing Bacillus subtilis reduced common scab by 56%. Since it affects almost any tuberous plant, keep in mind that it … Other root crops, including beets, carrots, radishes, and parsnips, are also susceptible to the disease. Reviewed by Extension Crops Specialist James Dwyer. The addition of manure may increase scab severity by providing a substrate for the organism, by increasing soil pH, or by being contaminated from animals fed scabby potatoes. Although there is no method known to completely control this disease, there are some management options that can help reduce the severity of common scab on potato. You’ll notice tan to dark brown, rough textured lesions where smooth flesh is supposed to be. Tubers with russetted scab can have large areas superficially covered with corky tissue. Individual lesions may coalesce, increasing the area of the tuber affected by the disease and exposing masses of resting spore aggregates. Common scab comes from a soil-borne bacteria Streptomyces scabies or Streptomyces species that seem to be found in most soils. Pitted scab can be as deep as one-half inch into the tuber. Sporeballs or sporosori of powdery scab, Spongospora subterranea, which germinate to produce swimming zoospores. The spores enter the tubers through wounds and lenticels. Severe infections may deform tubers, but the damage is typically aesthetic. However, few studies have shown effective and consistent control of common scab over many locations and years. Ten bacterial strains were isolated from CS-infected potato tubers from four different locations of Punjab, Pakistan, and identified based on biochemical and molecular analysis. In addition to Streptomyces scabies, Maine soils may have S. acidiscabies, which tolerates very acidic soils and is usually seed-borne, and S. turgidiscabies, which is also somewhat more tolerant of acidity. The organism can survive indefinitely in slightly alkaline soils, but is relatively scarce in highly acid soils. Streptomyces scabies is a saprophyte that can survive for long periods on decaying soil organic matter in the absence of hosts. There are a variety of means that research has shown to reduce common scab. Utilizing a disease suppressive rotation with green manures, such as buckwheat, canola, oat, rye or millet can inhibit Streptomyces scabies. Potato. Plants will resist a light frost, but har… Chloropicrin (Strike) is a soil fumigant that provides control of a number of soil borne diseases and has been reported to work well to reduce common scab. Unnamed products or companies implied are transformed into clickable links, few have! 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