Olive knot disease in Greece1

Abstract

Olive knot disease caused by Pseudomonas syringae subsp. savastanoi is widespread all over Greece where olive is grown and its severity varies from heavy in some areas and cultivars to very mild in others. Hypertrophied enlargements (galls or knots) more or less spherical in shape and up to 2.5 cm in diameter develop mostly on shoots, twigs, branches and trunks. Fruit infection, as roughly circular brown spots of 0.5‐2.5 mm in diameter, is another form of disease which develops during wet summers. All olive cultivars are equally susceptible to the pathogen. However, the differences in disease distribution and severity observed between cultivars and areas are directly related to the degree of wounding from whatever cause (frost, hailstorm, harvesting injuries), especially when they are accompanied by rainy and wet weather or moist winds. Harvesting by beating the trees with sticks is an important epidemiological factor for disease incidence in Greece. Suggested control measures are summarized.