Biological control of soil borne diseases in tobacco
Biotic stress components are one of the limiting factors for productivity in tobacco in India. Fusarium wilt caused by Fusarium oxysporum f.sp nicotianae (Mysore region) and Black shank caused by Phytophthora parasitica var. nicotianae (Northern Light Soils/NLS region) are two major soil borne diseases in flue-cured tobacco production. The control of these soil borne diseases in a single season is very difficult as these organisms are persistent in the soil for long periods. Chemical control measures are the ad hoc options to manage the disease during the crop season. But the non-chemical methods of pest and disease management are gaining importance in the current pesticide residue free tobacco production.
The objective of the study was to develop a non-chemical sustainable long term control option for soil borne disease management in tobacco. Successful bio-control options and deployment mechanism were worked out for the permanent control of these diseases. Trichoderma species were isolated from 42 tobacco soil samples and screened in vitro for the antagonistic activity against the pathogen. The best isolate of Trichoderma viride (ITC-3) was multiplied through a technique developed for the farm scale mass multiplication and used in the suppression of the pathogens. The Trichoderma viride strain, ITC-3, suppressed the pathogen and recorded control of 62-84 % in different fusarium wilt experimental trials (two random block designs [RBD] in two seasons). Application of 625 ml/ha (spore load of 2 × 10-9/ml) of Trichoderma liquid formulation was able to control black shank by 59-61 % over the control in two RBD trials conducted over two seasons. In bulk trials (three locations and two seasons), on the same piece of land, 98 % control of black shank was recorded by the second year in the NLS region. This practical and farmer friendly technique is effective in controlling fusarium wilt and black shank while addressing the pesticide residue problems.