|source image: agf.gov.bc.ca|
Ring rot disease of potato is a very infectious and destructive bacterial disease that is carried and spread by the tubers. The symptoms usually don’t appear until the plant has made most of its growth. Some of the stems in the hill may wilt, and they are often more or less stunted in growth. The remaining stems appear to be normal. Leaves of infected plants become pale yellowing at first, and within a few days a more pronounced yellowing develops. As the disease progresses, the leaves of potato curl upward and wilt. Leaf discoloration is accompanied by a progressive wilting which continues until all leaves are wilted and eventually the entire plant dies. If the stem of an infected plant is cross-sectioned with a knife, a creamy substance oozes out. When infected plants are dug, some tubers may appear normal, while others are in various stages of decay. Rotting appears first in the vascular region at the stem end of the tuber. In the early stages, rotting symptoms are rather indistinct; but after a time the entire vascular ring develops a creamy-yellow or light-brown color, and it breaks down into a crumbly, cheesy mass. Eventually, the entire tuber may rot.
How to control ring rot disease of potato?
The ring rot bacteria don’t live in the soil like the common scab or rhizoconia organisms, but instead are dependent upon the plants or tubers for survival from year to year. Thus, the only practical control is to plant seed that is free of the ring rot bacteria. Inasmuch as tubers may be infected without showing the symptoms, infected tubers can not al be discarded by inspection at planting time.
Because ring rot is extremely infectious healthy tubers may be infected by the cutting knives unless they are properly disinfected after cutting diseased tubers. A solution consisting of ½ ounce of mercuric chloride to 3 ½ gallons of water or one part of 40 per cent formalin to ten parts of water may be used to disinfect the knives. Planters, diggers, containers, elevators, grades, and the storage room should be disinfected with a solution consisting of one pound of copper sulphate to 10 gallons of water before using them again if an infected crop has been harvested and stored.
Delorit, Richard, et al. Crop production. Prentice-hall: New jersey