Biological control of soil-borne Phytophthora species on strawberry with bacterial antagonists .1. Antagonistic effect and colonization of rhizoplane

Fifteen antagonistic bacterial isolates out of the genera Agrobacterium, Bacillus, Enterobacter and Pseudomonas were used as biocontrol agents under both in vitro and growth chamber conditions against the soil-borne fungi Phytophthora cactorum and P. fragariae var. fragariae the causative agents of strawberry crown rot and strawberry red core disease. All isolates inhibited the mycelial growth of the pathogens in dual culture tests. In addition, four of the isolates reduced the root diseases on strawberry root system. The most inhibitory activity with a reduction of 68 % showed an isolate from Bacillus licheniformis against P. cactorum. As survival of biocontrol bacteria in soil and their colonization of root surface plays an important role for antagonism, rifampicin-resistant mutants of the most effective isolates were rested on their population dynamics on the rhizoplane. As result, st able concentrations of 10(4)-10(5) cfu/g root over 4 weeks could be detected.