Soft roguing induces recovery in Bois Noir infected grapevines

Bois Noir (BN), the main grapevine yellows in Central Italy, has been spreading through several European countries over the last years. This disease, caused by "Candidatus Phytoplasma solani", can result in severe crop losses and death of the vines. At present, there are no known effective control methods for controlling BN or other phytoplasmas. Roguing and transplanting of the vines infected by phytoplasmas can induce the phenomenon known as "recovery", whereby disease symptoms disappear from the canopy. In the Marche region, at the beginning of spring 2006, grapevines infected by BN were exposed to soft roguing, obtained by disrupting part of the root system using a small excavator. Plants of cvs Chardonnay, Sangiovese, and Verdicchio, grafted on Kober 5BB and trained as low cordon, were partially rogued and left in their position. Soft rouging induced recovery in all 5 plants of cvs Chardonnay and Verdicchio and in 4 out of 5 of cv. Sangiovese. The same experiment, carried out on grapevines of cv. Chardonnay grafted on 420A and trained as high cordon (single curtain), proved to be less effective. Such preliminary results show possible interactions between the type of rootstock and/or the training system and the effectiveness of soft roguing in the induction of recovery in BN-infected vines. An increased expression of the phenylalanine ammonia-lyase gene was observed in recovered plants.