Soft rot, Infection at two phases are black leg and soft rot. Black lesion appear on the base of the plant . Systemic and browning of infected tubers. Yellow appearance of the plant. Finally the plants wilt and die. Lenticels (water soaked brown rot). Rot andcollapse of tubers. Soft, reddish or black ring appear on the infected tuber.
Soft rot Pathogen
It is a gram negative rod shaped bacterium with 1 to 6 peritrichous flagella.
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Soft rot Mode of spread and survival
Infected tubers attract the flies (Hymelia and Phorlin sp). Spread throughimmature contaminated soil and tuber. Optimum temperature 21 to 29 ºC and RH 94%
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Soft rot Management
The pathogen is difficult to control because of long survival both on seed tubers and in soils. However using disease free seed tubers could minimize the disease incidence. Before planting the seed tubers are treated with Boric Acid (3% for 30 minutes) and dried in shade. The same treatment is repeated before the storage of the tubers.The disease can be reduced by soil application of PCNB (30 kg/ha) at the time of planting. Following crop rotations with wheat, pea, oats, barley, lupin, soybean, sorghum and bajra checks the disease development. In plains, treatment of the seed tubers with TBZ + acetic acid + 0.05% Zinc Sulphate solution or Carbendazim 1% for 15 minutes effectively controls the disease. Soaking of tubers in Mercuric chloride 0.1% formalin.