Combining fluorescent Pseudomonas spp. strains to enhance suppression of fusarium wilt of radish

Fusarium wilt diseases, caused by the fungus Fusarium oxysporum, lead to si gnificant yield losses of crops. One strategy to control fusarium wilt is t he use of antagonistic, root-colonizing Pseudomonas spp. It has been demons trated that different strains of these bacteria suppress disease by differe nt mechanisms. Therefore, application of a mixture of these biocontrol stra ins, and thus of several suppressive mechanisms, may represent a viable con trol strategy. A prerequisite for biocontrol by combinations of biocontrol agents can be the compatibility of the co-inoculated micro-organisms. Hence , compatibility between several Pseudomonas spp. strains, that have the abi lity to suppress fusarium wilt of radish, was tested in vitro on KB agar pl ates. Growth of P. fluorescens strain RS111 was strongly inhibited by Pseud omonas spp. strains RE8, RS13, RS56 and RS158, whereas a mutant of strain R S111 (RS111-a) was insensitive to inhibition by these strains. Strains RS11 1 and RS111-a only slightly inhibited some other strains. Suppression of fu sarium wilt of radish in a potting soil bioassay by the incompatible combin ation of RE8 and RS111 was comparable to the effects of the single strains. However, disease suppression by the compatible combination of RE8 and RS11 1-a was significantly better as compared to the single strains. In contrast , the incompatible combination of RS56 with RS111 resulted in enhanced dise ase suppression as compared to the single strains. Increased disease suppre ssion by combinations of RS13 or RS158 with RS111 or RS111-a was not observ ed. This indicates that specific interactions between biocontrol strains in fluence disease suppression by combinations of these strains.