Characterization and Prevalence of Different Isolates of Pseudomonas savastanoi and Pathogenicity Properties on Olive and Oleander Plants

This study investigated the distribution and epidemiology of Pseudomonas savastanoi pv. savastanoi (Pss), the causal agent of olive knot disease, in major olive-growing provinces of Southeastern Anatolia, Turkey, between 2019 and 2021. Field surveys in Adıyaman and Mardin revealed knot symptoms on olive shoots, and Pss isolates were successfully obtained from symptomatic tissues. Biochemical assays on King’s B medium identified all strains as Gram-negative, oxidase-negative, pectolytic activity-negative, and arginine dihydrolase-negative while showing a positive hypersensitive reaction. Among the four isolates, two were levan-positive and non-fluorescent, whereas two were levan-negative and fluorescent. PCR with IAALF and IAALR primers amplified a 454 bp fragment in all isolates, confirming their identity as Pss. Pathogenicity assays on carrot slices and olive plants verified their pathogenic nature. Virulence tests demonstrated that infection severity was highest in pink oleander, followed by olive and white oleander. Disease incidence differed markedly between provinces, averaging 0.017% in Adıyaman and 33.28% in Mardin, with Derik district reaching 50.37% incidence and 100% prevalence. A novel infection-area-based method yielded results consistent with knot size assessments. These findings confirm the pathogenic potential and host range of Pss in Southeastern Anatolia and emphasize the importance of monitoring, epidemiological assessment, and management strategies.