Pseudomonas putida has potential for biological control of bacterial spot of tomato, caused by Xanthomonas euvesicatoria

Bacterial spot of tomato, caused by Xanthomonas euvesicatoria, is a serious disease that causes yield and quality losses. There has been increased focus on biological control agents as alternatives to chemical pesticides in plant disease management. In this study, 313 endophyte and epiphyte bacterial isolates, from tomato plants sampled from different locations in Turkey, were assessed for their potential for plant growth promotion and biocontrol efficacy against X. euvesicatoria. Results obtained from in vitro assays were evaluated using the weighted ranking method, and 15 isolates were selected for in planta biocontrol evaluation against X. euvesicatoria. In efficacy tests, bacteria were introduced into tomato plants by biopriming of seeds or by spraying whole plants. The two most effective isolates reduced bacterial spot by 40-45% after seed biopriming, and 30-41% from shoot application, compared to the non-treated experimental controls. Sequence analysis using 16S rRNA primers identified one representative isolate (coded KD 91/1) as Pseudomonas putida. Tomato plants bioprimed with KD 91/1 through seed treatment had greatest biomass compared to that for the other tested bacteria. The population of P. putida KD 91/1 in tomato tissues after pathogen inoculation was approx. 7.2 x 10(4) cfu g(-1) in shoots and 1 x 10(5) cfu g(-1) in roots. This study indicates that antagonistic P. putida isolates are promising candidates for biological control of X. euvesicatoria.