Introducing the potential biological control agent Frateuria defendens into pot- and field-grown grapevines

Bois Noir is a major yellows disease in grapevine with no current means of control. The endophyte Frateuria defendens (Frd), isolated from the insect vector of Bois Noir, is a potential biocontrol agent for this disease. The aim of this study was to determine an efficient way to introduce Frd into mature vines under field conditions. Shoots of young and field-grown vines were sprayed with Frd suspension supplemented with either Tween 20, BB5, DX, or Triton X-100 as surfactants. The presence of Frd was confirmed by PCR in sprayed leaves, and in leaves below and above the sprayed site. The results showed that cells of Frd penetrate and move inside the vine shoots under field conditions. Highest penetration rate was achieved when leaves were sprayed with 10(8) or 10(9) colony forming units per \mL (CFU mL(-1)) of Frd with addition of 0.1% Tween 20. The addition of a surfactant is essential to increase the proportion of shoots with Frd.