Shikha Pathak and Desh Raj Shri Bharati
PhD Research Scholar
Dept. of Plant Pathology, BCKV, West Bengal
Soil is a niche for diverse group of microorganisms which may be beneficial or harmful to humans as well as plants. Soil borne diseases are caused by harmful microorganisms dwelling in soil by means of resistant survival structures such as melanized hyphae, chlamydospore, oospores and sclerotia in case of many fungi, others survive on host plant debris, organic matter or as free living organisms. Many microorganisms such virus, bacteria, fungus, nematodes and others present in soil are pathogenic to plant and usually colonize by infecting roots or collar region of plants leading to successful disease. Soil-borne diseases may include pre and post-emergence damping-off, root and collar rot, vascular wilts caused by fungi and bacteria, cyst and knots in root caused by nematodes. In direct seeded vegetable crops pre- emergence damping off is quite common whereas in transplanting type post emergence damping off reduces the plant population.
The soil inhabiting pathogens infects the roots or collar region of plants which hampers further development of plants therefore diseases caused by such pathogens can be a major limitation for vegetable production thereby leading to economic losses. The diseases like collar rot or root rot disease is prevalent in both woody and herbaceous vegetable plants. There is disintegration of tissues in collar region between stem and root or in roots which leads to death of plant. In vascular wilts, the transportation of water and minerals and translocation of food materials in infected plants gets blocked leading to wilting and death of the plant. The cysts and knots caused by the nematode in root zone hampers the absorption capability of roots and thereby the growth and development of plant is adversely affected.
Management of soilborne disease becomes very difficult as they are caused by pathogens which can survive for long periods in the absence of the normal crop host and often have a wide host range which includes weeds. Also, these diseases are not visible at initial stage and sometimes the accurate diagnosis becomes difficult. Because of their extremely small size and non-specific symptoms of infection, soilborne pathogens live out of sight and, generally out of mind of the growers. The effective management of the soilborne diseases is possible only through knowledge of survival, dissemination of soilborne pathogens, effect of environmental conditions, role of cultural practices and host resistance and susceptibility. Above all the growers must focus on the field sanitation where the field prior to sowing or transplanting is free from all sort of infected plant parts. Curing is difficult so one should focus on the practices leading to prevention of soilborne diseases. Timely and prophylactic care to manage soil borne pathogens will provide dividends of potential harvest of the crops.