Epiphytic Pseudomonas savastanoi pv. savastanoi can infect and cause olive knot disease on Olea europaea subsp. cuspidata

Abstract

Endophytic and epiphytic survival and population growth of Pseudomonas savastanoi pv. savastanoi (Psav), the causal agent of olive knot disease, were studied for the first time in Olea europaea subsp. cuspidata. Five different strains of Psav, isolated from different geographic areas, were inoculated into wounds of O. europaea subsp. cuspidata and European olive (O. europaea subsp. europaea) plants that were 3, 9, or 20 months of age to evaluate endophytic survival. Epiphytic survival of two strains of Psav sprayed on leaves of 2-year old plants was also assessed. Pathogenicity tests showed that O. europaea subsp. cuspidata is susceptible to Psav. Pathogen survival and population growth rates did not differ significantly between the two olive subspecies. No correlation was observed between knot weight and endophytic pathogen population density. Plant age did not significantly influence the host–pathogen interaction. Epiphytic survival showed that Psav, regardless of strain, reproduced better on O. europaea subsp. cuspidata than on the European olive. Together, these results indicate that control measures are necessary to prevent the spread of introduced Psav in areas where O. europaea subsp. cuspidata is native.