Investigation on the combined use of plant growth promoting rhizobacteria and Trichoderma species against wilt disease of eggplant

In this thesis, effects of single and combined applications of biocontrol agents Trichoderma spp. and plant growth promoting rhizobacteria (PGPR) on growth, wilt disease severity caused by Fusarium oxysporum f. sp. melongenae and Verticillium dahliae and plant defense related enzymes (peroxidase, polyphenol oxidase, phenylalanine ammonium lyase and β-1,3 glucanase) of eggplant were investigated. From the plant and soil samples taken from the eggplant cultivation fields of West Mediterranean region, 156 bacteria and 14 Trichoderma isolates were obtained. In vitro dual culture experiments showed that six bacteria and seven Trichoderma isolates inhibited the growth of two pathogens. By using similar dual culture experiments performed to determine the growth of biocontrol agents together, two bacteria (P. koreensis and B. subtilis) and two Trichoderma (T. virens and T. atroviride) isolates compatible with each other were selected for in vivo trials. Enzymatic activities of the biocontrol agents related with their antagonistic effects against pathogens were also investigated. It was found that three PGPR isolates had cellulase activity, while four had protease and two had chitinase activity and five bacteria isolates produced siderophores. Enzyme values obtained by Trichoderma isolates were between 108.861-116.917 µg/ml for cellulase, 659.524-407.143 µg/ml for chitinase, and 273.382- 291.03 µg/ml for β-1,3 glucanase. In vivo experiments showed that single or combined use of biocontrol agents decreased the severity of wilt disease caused by the pathogens, and caused increase of plant growth parameters and activities of plant defense related enzymes.