Auxin-treatment induces recovery of phytoplasma-infected periwinkle

To test the effect of auxin-treatment on plant pathogenic phytoplasmas and phytoplasma-infected host. In vitro grown periwinkle shoots infected with different 'Candidatus Phytoplasma' species were treated with indole-3-acetic acid (IAA) or indole-3-butyric acid (IBA). Both auxins induced recovery of phytoplasma-infected periwinkle shoots, but IBA was more effective. The time period and concentration of the auxin needed to induce recovery was dependent on the 'Candidatus Phytoplasma' species and the type of auxin. Two 'Candidatus Phytoplasma' species, 'Ca. P. pruni' (strain KVI, clover phyllody from Italy) and 'Ca. P. asteris' (strain HYDB, hydrangea phyllody), were susceptible to auxin-treatment and undetected by nested PCR or detected only in the second nested PCR in the host tissue. 'Ca. P. solani' (strain SA-I, grapevine yellows) persisted in the host tissue despite the obvious recovery of the host plant and was always detected in the direct PCR. Both auxins induced recovery of phytoplasma-infected plants and affected tested 'Candidatus Phytoplasma' species in the same manner, implying that the mechanism involved in phytoplasma elimination/survival is common to both, IAA and IBA. The results imply that in the case of some 'Candidatus Phytoplasma' species, IBA-treatment could be used to eliminate phytoplasmas from in vitro grown Catharanthus roseus shoots.