Phenotypic and Molecular Diversity of Pseudomonas savastanoi pv. savastanoi Strains Causing Olive Knot Disease

Abstract

Phenotypic and molecular diversity of Pseudomonas savastanoi pv. savastanoi strains causing olive knot disease was investigated to elucidate variation in pathogenic populations associated with disease severity and spread. Field surveys were conducted in olive orchards exhibiting characteristic knot formation, galling on stems, and reduced vegetative growth. Bacterial isolates were obtained from infected tissues and characterized based on colony morphology, biochemical traits, pigment production, and growth behavior under standard culture conditions. Molecular characterization was performed using PCR amplification and sequencing of housekeeping and virulence-associated genes to assess genetic variability and phylogenetic relationships among strains. Results revealed considerable phenotypic variation in traits such as mucoid production, growth rate, and aggressiveness, indicating functional diversity within the pathogen population. Molecular analysis demonstrated clustering of isolates into distinct genetic groups, suggesting the presence of multiple lineages associated with olive knot disease. Pathogenicity assays on olive seedlings confirmed significant differences in virulence, with highly aggressive strains inducing rapid knot formation and severe gall development. A correlation between molecular grouping and pathogenic potential was observed, highlighting the epidemiological relevance of genetic diversity. The study underscores the importance of integrating phenotypic and molecular approaches for accurate characterization of P. savastanoi populations. These findings contribute to improved understanding of disease dynamics and support the development of targeted management strategies for olive knot disease.