Potato scab is caused by the bacterium Streptomyces scabies. This bacterium is related to certain bacteria that produce antibiotics used to treat human diseases. What do I do with potato tubers that have potato scab? Scabby potato tubers, while unsightly, are still edible. Infected potatoes need only be peeled before use. Store tubers with scab in a cool, dark, dry place to reduce the possibility of scabby areas becoming infected by soft rot bacteria that will totally decay tubers. How do I avoid problems with potato scab in the future?
Use certified, scab-free seed potatoes in your garden. DO NOT use infected tubers to produce seed pieces. Select potatoes varieties such as Norland, Russet Burbank and Superior that have at least moderate resistance to scab.
Try not to plant potatoes in the same spot in your garden more frequently than once every three years. Rotate potatoes with crops such as corn, peas, and beans that are not susceptible to scab. Scab problems tend to disappear when soil pH is less than 5. Therefore, acidify garden soils i. Common scab of potato.
Quick facts. Common name: Common scab and powdery scab Scientific name: Streptomyces spp. Timing: Summer. Jump to What are potato scabs? Symptoms Control Biology. What are potato scabs? Symptoms 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.
These areas contain masses of dusty brown spores Severe attacks of powdery scab can lead to massive distortion of tubers, reminiscent of wart disease caused by Synchytrium endobioticum , a serious but now very rare potato disease. Powdery scab Spongospora subterranea , in this case also causing some distortion at one end of the tuber in most cases distortion isn't present.
Control Non-chemical control Select seed carefully and avoid planting seed potatoes that have visible signs of scab. Legislation controls the amount of infection allowed in seed, but low levels are permitted To control common scab, do not allow the soil to become dry during tuber development.
Raise organic matter levels to improve water retention. Water the developing crop if necessary, starting two to three weeks after plants emerge and continuing for about four weeks, applying 20 litres per sq m 4 gallons per sq yd Common scab is worse on alkaline soil, so liming the soil to prevent club root of brassicas will predispose to common scab in potatoes.
Apply lime after the potato course of the rotation Choose resistant cultivars. For more information visit The British Potato Variety Database Chemical control There are no chemical controls available to gardeners for either disease.
Biology Both the common and powdery scab pathogens are sometimes described as fungi, but in fact Streptomyces species are more closely related to bacteria and Spongospora subterranea f.
You may also like. Potato and tomato blight. Potato black scurf and stem canker. Potato blackleg. However, sometimes when the potato crop is lifted, there are unwanted ugly, scabby lesions—blemishes that spoil the appearance of the tuber and make them undesirable to consumers or difficult to process Figure 1.
This all too common problem is generally referred to as common scab. I get multiple calls each year about common scab and what can be done to control this disease. For this article, I wanted to summarize the biology of common scab and discuss what research has found to reduce common scab on potatoes. As we all start thinking about the crop, I hope this article will help us all understand common scab better. Common scab comes from a soil-borne bacteria Streptomyces scabies or Streptomyces species that seem to be found in most soils.
There are hundreds of bacterial species in the Streptomyces genus. This could explain why a potato cultivar may not be affected by common scab in one area, but have severe scab when planted in another geography.
It can be difficult to visually determine the difference between common scab and powdery scab. A laboratory analysis is always a good idea to get the correct diagnosis. 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.
The spores enter the tubers through wounds and lenticels. Young lenticels are thought to provide entry to Streptomyces species. Once in the plant, Streptomyces scabies produces a phytotoxin called thaxtomin that breaks down cell walls and penetrates rapidly growing cells. As the potato plant cells die, they produce cork cells that push outward and form a scab lesion. As these cork cells continue to develop, the lesions grow larger.
The type of scab raised, superficial or pitted varies based on the potato cultivar, environment and soil microbial community. Tubers are most susceptible to infection of Streptomyces species during the first three to four weeks after tuber initiation, when compared to six to eight weeks after tuber initiation. Early infection can lead to deeper scab lesions on the tuber.
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