Economically significant bacterial and viral diseases of potato and their management

In India, about 80 per cent of potato crop is cultivated under subtropical and 20 per cent under temperate to sub-temperate climate. The cultivation of this crop is often affected due to attack of various diseases caused by bacteria and viruses. Among bacterial diseases soft rot Erwinia spp., Bacterial wilt caused by Pseudomonas solanacearum, the brown rot pathogen Ralstonia solanacearum, the ring rot pathogen Clavibacter michiganensis subsp. sepedonicus and the scab forming Streptomyces spp. Commercial propagation of potato is normally done vegetatively using ‘seed’ tubers. Therefore, ‘Degeneration’ of seed stocks due to viruses is common as vegetative propagation results in the continuity of several viral pathogens. There are over 30 viruses infecting potatoes, but only five or six are actually important in India/ S. Asia. The losses in potato yield due to one or more virus(s) infecting potatoes vary from low to very high. Generally severe mosaic caused by potato virus Y (PVY) and potato leaf roll virus (PLRV) alone can reduce the yields up to 70-80% while mild viruses, like PVX, PVS, PVM also depress the yields by 10-30%. If the seed stocks are not maintained well or frequently replaced with fresh ones, the virus infiltration reaches 100% level within 3-4 successive crop seasons/years resulting in almost only half to one third yields which is rather uneconomical. In the past two decades, several systemic fungicides and insecticides with significantly better efficacy have been found promising these economically important diseases. Microorganisms that can grow in the rhizosphere are ideal for use as biocontrol agents.