Evaluation of effective microorganisms® efficacy on 'Candidatus Phytoplasma solani'-infected and healthy periwinkle plants

A sustainable approach to control plant diseases concerns the employment of bacteria promoting induced systemic resistance (ISR) and/or directly antagonizing the pathogens. In the present study, we tested the efficacy of the commercial product EM (Effective Microorganisms) on periwinkle plants infected by 'Candidatus Phytoplasma solani' (CaPsol), the etiological agent of Bois noir disease (BN) of grapevine. Sequence analyses confirmed the affiliation of CaPsol (strain STOL), transmitted to healthy periwinkle plants by grafting, to 16SrXII-A/tuf-B type. Experiments were performed to evaluate both preventive and curative EM efficacy by treating roots of periwinkles (ungrafted, grafted with healthy scion, grafted with infected scion). Untreated periwinkles were used as controls. Starting from the 20th day, CaPsol-symptoms along with a drastic reduction of the photosynthetic activity, measured as F-v/F-m, were observed in treated and untreated plants infected by grafting, without significant difference. However, higher Fv/Fm values were registered in treated ungrafted plants in comparison with treated plants grafted with healthy scion. Such evidences suggested that (i) EM (R) treatment stimulated the plant growth; (ii) grafting induced stress to the plants compromising the evaluation of EM efficacy. Further studies were planned to investigate the effects of EM on BN-affected grapevine in controlled conditions and in open field.