Use of Bacillus subtilis as biocontrol agent. II. Biological control of potato diseases

Biological control of stem canker and black scurf of potatoes caused by Rhizoctonia solani and common potato scab caused by Streptomyces scabies by different suppressive strains of Bacillus subtilis was demonstrated in greenhouse and field experiments from 1993-1937. Seed potatoes were treated with different strains of Bacillus subtilis, formulated to water-dispersible granules and were planted in comparison with nontreated (control) and fungicide (Pencycuron, tolclofos-methyl) treated potatoes in greenhouse or in field against natural seed- and soil-borne infection. In addition, the influences of different edaphic and other abiotic factors were tested, e.g., various soil types, different inoculum densities, various application methods, and application races. In the greenhouse, the disease severity of R. solani (stem canker and black scurf) was reduced up to 63 % by application of B, subtilis. The decrease of common scab (S. scabies) disease severity ranged up to 70 % with different Bacillus strains. In field trials, the occurrence of stem canker and blade scurf was reduced up to 50 % and the incidence of common scab was decreased up to 67 % by use of this microbial antagonist. The bacterial treatment showed similar control effects compared to different fungicides. Moreover, the plants appeared more vigorous than nontreated plants and the yields of potato tubers were higher (on average up to 16 %).