Preparation of Bacillus subtilis capsule formulation and evaluation of its efficacy in controlling damping-off in tomato caused by Rhizoctonia solani under greenhouse conditions

The use of biocontrol agents is a promising and safe method towards achieving environmental goals for controlling plant diseases. However, due to the lack of stability and appropriate and applicable formulations, the results obtained from the application of these agents, especially in agricultural fields, have not been sufficiently efficient. This study was conducted with the aim of developing a capsule formulation using sodium alginate to increase the viability and improve the performance of Bacillus subtilis. Capsules were prepared using the ionic gelation method. The encapsulation efficiency was estimated to be 99%. The mean size of the wet and dry capsules produced was 2600 and 1000 micrometers, respectively. The effects of ultraviolet radiation on the survival of B. subtilis showed that the bacterium in the capsule state (wet and dry) was more resistant to ultraviolet radiation compared to the non–encapsulated state. With increasing exposure time to ultraviolet light, bacterial cells resistance in the capsule state were greater than in the non–encapsulated state. The results of the thermal resistance examination at different temperatures emphasized the positive role of the capsules in increasing the survival and resistance of B. subtilis compared to the non–encapsulated state. The survival percentage of non–encapsulated B. subtilis after 60 days at 25 and 35 degrees Celsius decreased by 42% and 47%, respectively. However, for the encapsulated B. subtilis, the survival percentage decrease after the same period and temperature was estimated to be 16.5% and 26%, respectively. Greenhouse results showed that the use of B. subtilis capsule formulation reduced disease percentage compared to non–encapsulated B. subtilis and sodium alginate capsules alone. The disease percentage in plants treated with encapsulated B. subtilis was estimated to be 4.44%, while this rate was 73.33% in the control. Plants treated with encapsulated B. subtilis had significant differences in growth indices compared to the control. Growth index changes in relation to different formulations of B. subtilis (encapsulated, non–encapsulated) and sodium alginate capsules alone were significant only for root height. These results emphasize the positive role of using B. subtilis and capsule formulation in controlling damping–off caused by Rhizoctonia solani in tomato plants.