USE OF BACILLUS-SUBTILIS AS BIOCONTROL AGENT - II - BIOLOGICAL-CONTROL OF POTATO DISEASES

Biological control of stem canker and black scurf of potatoes caused b y Rhizoctonia solani and common potato scab caused by Streptomyces sca bies by different suppressive strains of Bacillus subtilis was demonst rated in greenhouse and field experiments from 1993-1937. Seed potatoe s were treated with different strains of Bacillus subtilis, formulated to water-dispersible granules and were planted in comparison with non treated (control) and fungicide (Pencycuron, tolclofos-methyl) treated potatoes in greenhouse or in field against natural seed- and soil-bor ne infection. In addition, the influences of different edaphic and oth er abiotic factors were tested, e.g., various soil types, different in oculum 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 antag onist. 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 %).