Detection of olive knot (Pseudomonas savastanoi pv. savastanoi) disease in Hatay province and investigation of biological control possibilities

The aim of this study was to determine the prevalence and incidence of olive knot disease in Hatay province and the biological control possibilities of Pseudomonas savastanoi pv. savastanoi by using epiphyte and endophyte bacteria isolated from the roots and shoots of healthy olive trees. The highest prevalence rate of the disease was determined in Samandağ, İskenderun and Arsuz districts with 90 % and no disease incidence was detected in Hassa, Kırıkhan, Reyhanlı and Kumlu districts. The incidence of the disease in infected gardens varied between 4.5-75%. The causal disease agent was identified by Gram stain, LOPAT, MALDI-TOF and molecular techniques. All strains were determined as gram negative, levan negative, oxidase negative, pectolytic activity negative, arginine dehydrolase negative, but tobacco hypersensitivity reaction was positive. According to the test results, a total of 14 isolates were identified as Pseudomonas savastanoi pv. savastanoi. In biological control studies, a total of 362 bacteria (218 epiphytes and 144 endophytes) were isolated and diagnosed by using MALDITOF-MS. In dual culture tests, 81 epiphyte and endophyte bacterial isolates inhibited pathogen development at different rates. The highest inhibition rate (A-indeks) was determined in Bacillus megaterium HZEP7 isolate with 5.24 A-index value, followed by Bacillus subtilis HZEN1 (4.85) and Pseudomonas koreensis HZEN27 (4.83), respectively. Mechanisms of epiphyte and endophyte bacteria such as indole acetic acid (IAA) production, siderophore production, determination of phosphorus dissolving potentials, protease production and ammonia production were investigated by in vitro tests. The isolates to be used in in vivo tests have been determined according to high antagonistic effect, low IAA production and other mechanisms, and Bacillus subtilis HZEN1, Bacillus megaterium HZEP7, Pseudomonas koreensis HZEN27 and Bacillus pumilus HZEP29 isolates have been selected for determination of biocontrol effect by carrot slices and seedlings inoculation. In the tests for determination of the biocontrol effect by carrot slices inoculation, the highest inhibition was detected in Bacillus subtilis HZEN1 isolate with 98.78%, followed by Bacillus megaterium HZEP7 (94.49%), Pseudomonas koreensis HZEN27 (92.09%) and Bacillus pumilus HZEP29 (90.26%) isolates, respectively. Similar to carrot slices in seedling inoculation tests, all bacterial isolates inhibited gall formation. The highest inhibition was determined in Bacillus subtilis HZEN1 isolate with 78.72%, followed by Bacillus megaterium HZEP7 (60.87%), Pseudomonas koreensis HZEN27 (46.09%) and Bacillus pumilus HZEP29 (44.87%) isolates, respectively. In addition, the gall formation was inhibited by 48.23% in copper sulphate application. The obtained results showed that Bacillus subtilis HZEN1, Bacillus megaterium HZEP7, Pseudomonas koreensis HZEN27 and Bacillus pumilus HZEP29 isolates could be used against olive knot disease as a biocontrol agent.