Determination of Antagonistic Potential of Epiphytic and Endophytic Bacterial Isolates Against Apple Crown Gal Disease Agent Rhizobium radiobacter

Crown gal disease, caused by Rhizobium radiobacter (formerly known as Agrobacterium tumefaciens), is one of the most important bacterial plant disease of stone fruits, pome fruits, grape vine, vegetable and ornamental plants distributed worldwide. Disease causes considerable damage in nursery and young orchards of variety of plants including apple where grower may suffer serious economic losses as galled plants show growth reduction and yield. Different control measures have been used against crown gall as a dipping of rooted plants into chemicals, soil fumigation, soil solarization and biological control. The aim of this study was to determine biocontrol efficacies of epiphytic and endophytic bacteria, obtained from apple roots and crowns, against crown gall disease agent. Eighty five putative epiphytic and endophytic antagonist bacterial isolates were obtained from the apple rhizosphere, roots and crown. By using dual culture test, putative antagonist bacterial isolates were screened for their ability to suppress disease agent R. radiobacter in vitro conditions. According to the results obtained from the preliminary dual culture test, 12 isolates, belonging to different bacterial species of Pseudomonas, Pantoea, Serratia and Bacillus genus were found to cause clear inhibition zones of 5.0-27.3 mm diameter. Among the tested antagonist isolates, three different bacterial isolates of Pseudomonas putida 1-4en, 1-12en and 1-13en were then chosen for semi in vivo studies which were conducted on carrot slice assay. Among these isolates, the most efficient bacterial isolate 1-14en significantly suppressed gall formation on carrot slices. Results of this study revealed that antagonist bacterial isolates of Pseudomonas putida has potential as biocontrol agent for crown gall disease caused by Rhizobium radiobacter