Immature walnut fruit inoculation for evaluation of Brenneria nigrifluens pathogenicity

Abstract

A reliable, reproducible, rapid and specific test for the pathogenicity of Brenneria nigrifluens, the causal agent of shallow bark canker of Persian walnut, was developed. When the mesocarp of immature walnut fruits was infiltrated by syringe with bacterial suspensions (108 cells mL^-1) of B. nigrifluens, necrosis and reddish brown exudates started to appear at the inoculation sites, as early as 2 days after inoculation. No symptoms were detected in control fruits or in fruits inoculated with other bacteria frequently associated with walnut cankers. This pathogenicity test saves time and space when compared with the plant stem inoculation technique, in which the canker symptoms do not appear until at least 1 month after inoculation.