Application of plant growth-promoting rhizobacteria (PGPR) in combination with a mild strain of Cucumber mosaic virus (CMV) associated with viral satellite RNAs to enhance growth and protection against a virulent strain of CMV in tomato

An indigenous strain of Cucumber mosaic virus (CMV) associated with a naturally occurring benign viral satellite RNA (345 bp long), referred to as CMV-KU1, although effective as a protective biocontrol agent against the damaging effects of the virulent CMV-16 strain, produced negative side-effects such as mild stunting, vigour reduction and about 20% yield loss in tomato (Solanum lycopersicon L.) plants. The efficacy of using a mixture of two plant growth-promoting rhizobacteria (PGPR) strains, Pseudomonas aeruginosa and Stenotrophomonas rhizophilia, to compensate for vegetative and yield loss caused by CMV-KU1 in tomato plants, was evaluated in greenhouse experiments. In addition to promoting plant growth, PGPRs are known to enhance systemic defences in plants against foliar pathogens such as viruses that attack tissues distant to PGPR sphere of activity. The use of PGPR and CMV-KU1 together successfully promoted vegetative growth and fruit yield in tomato plants to values equivalent to that of the healthy controls. The combination used also enhanced overall protection of the plants against the severe CMV-16 virus with about 91.3% disease prevention. Serological analysis using enzyme-linked immunosorbent assay (ELISA) also indicated a lower incidence of CMV-16 infection in protected test plants.