Biological control of red stele (Phytophthora fragariae var. fragariae) and crown rot (P. cactorum) disease of strawberry with rhizobacteria

After in vitro screening of more than 100 bacterial isolates from the rhizosphere on their antagonistic effect against Phytophthora fragariae var. fragariae and P. cactorum, the two causal agents of red stele and crown rot disease of strawberry, three bacteria out of different genera Raoultella terrigena (G-584), Bacillus amyloliquefaciens (G-V1) and Pseudomonas fluorescens (2R1-7) were found with the highest inhibitory effect on the mycelial growth of both Phytophthora spp. For the management of both fungal diseases the antagonistic bacteria were further evaluated under greenhouse and field conditions. In greenhouse all three bacteria were significantly effective in reducing red core and crown rot, exhibited a similar level of control as the chemical fungicide Aliette of up to 59%. In field trials conducted at different locations in Germany under artificially and naturally infested soil conditions in two season 2003 to 2005, different level of biocontrol was performed by the tested bacteria. In trial of the first season under artificial conditions, the three rizhobacteria showed a significant control up to 45% against both diseases and in the next season, only B. amyloliquefaciens was effective against red stele. Under natural conditions, significant effect of 37.5% was observed from a mixture of R. terrigena and B. amyloliquefaciens in first season and in second season R. terrigena showed significant effect of 45.1% in the northern part of Germany. In the south, R. terrigena and B. amyloliquefaciens were significantly efficient up to 51.5% and the overall effect were similar to Aliette.