Detrimental effect of quercetin on phytoplasma-infected Catharanthus roseus (L.) G. Don shoots grown in vitro

Quercetin is known to possess antimicrobial activity against bacteria, fungi, and viruses. The activity of this flavonoid against phytoplasmas, non-cultivable plant pathogenic bacteria that cause numerous plant diseases, has never been examined before. The aim of this research was to examine the effect of different concentrations of quercetin (10 mu M, 100 mu M and 1 mM) on 'Candidatus Phytoplasma asteris' and on phytoplasma-infected periwinkle shoots grown in vitro. The addition of quercetin neither supported the growth of the shoots nor induced the remission of symptoms in the infected plants. On the contrary, addition of quercetin induced browning of leaves and the appearance of black spots on the leaves of treated infected and non-infected shoots. It also had no curative effect against the pathogen. Phytoplasma presence was confirmed by nested PCR in infected shoots treated with quercetin through three subcultures.