Biological control of tomato wilt caused by Ralstonia solanacearum and Fusarium oxysporum f. sp lycopersici by rhizobacteria

Replacing the intensive use of pesticides for alternative methods in disease control has been an important aim for agricultural research. Rhizobacteria are known to be capable of reducing diseases levels in many crops and also of promoting plant growth. The objective of this work was to evaluate the efficacy of six pre-selected rhizobacteria isolates in controlling Ralstonia solanacearum and Fusarium oxysporum f. sp. lycopersici (FOL) under controlled conditions in a greenhouse, and to link such capacity to the in vitro production of selected biologically active compounds. The ability of these rhizobacteria isolates to produce chitinases, amylases, lipases, antibiotic compounds was investigated. Additionally, their ability in solubilizing phosphate was also checked. Microbiolization of seeds with one rhizobacterium DFs1421 (Pseudomonas sp.) reduced the tomato wilt AUDPC in both assays (36.6 and 91.7% in the first and second assays respectively). Such efficacy in wilt control is likely to be linked with the production of antibiotics as observed in vitro. Streptomyces (DFs1296 and DFs1315) and Bacillus (DFs1414), and the chemical inducer (ASM) reduced significantly fusarium wilt ranging 22.5 to 76%. This may be owing to the observed chitinolytic activity and / or antibiosis in the presence of volatile compounds.