FIG. 4.

Virulence expressed as percentages of wilted twigs after inoculation of P. avellanae strains (group A) and other fluorescent pseudomonads (group B) pathogenic for C. avellana cv. Tonda Gentile Romana (A) and C. avellana cv. Tonda Gentile delle Langhe (B). Bacterial suspensions in sterile saline were photometrically adjusted to an optical density corresponding to 1 × 10⁷ CFU ml⁻¹. Serial 10-fold dilutions up to 1 × 10³ CFU ml⁻¹ were prepared. Ten microliters of a suspension was placed on each leaf scar. Symbols: ▪, subgroup A1; ⧫, subgroup A2; ×, subgroup B1; ▴, subgroup B2; •, subgroup B3; X, subgroup B4.