Reactions of some cultivars of Olea europaea L. to experimental inoculation with Pseudomonas syringae pv. savastanoi.
Olive knot, caused by Pseudomonas syringae pv. savastanoi [P. savastanoi], is a relatively common disease contributing to a decrease in crop yield in olive trees in Portugal. A study was conducted in order to determine resistance to that disease by experimentally inoculating young plants of the cultivars Galega Vulgar, Branquita (syn. Blanqueta), Cordovil de Serpa, Cobrançosa, Redondil and Santulhana. Bacterial isolates were initially obtained from infected trees of Galega Vulgar, and grown in pure culture in PDA medium. Three µl of bacterial suspension, containing 5 × 108 cells per ml, were inoculated onto stems of young plants growing in pots under high temperature and high humidity in the greenhouse. Observations were made at 9, 15, 22, 29, 45 and 90 days after inoculation. The presence of outgrowths (tumours) in the plants was interpreted as a positive or susceptible reaction. Although controls remained tumour-free, 4 of the cultivars exhibited some symptoms, identical to those observed in the field, while Cobrançosa and Redondil appeared to be more resistant.