Preliminary evaluation of a zinc-copper-citric acid biocomplex for the control of Plenodomus tracheiphilus causal agent of citrus mal secco disease

In this study we evaluated a zinc copper-citric acid biocomplex (Dentamet®) for the effect on citrus mal secco disease caused by Plenodomus tracheiphilus. In vitro tests highlighted an inhibitory activity of the compound on mycelial growth and phialoconidia germination. Independent in vivo trials were performed in a growth chamber inoculating a virulent fungal isolate on sour orange seedlings and young plants of two lines of Femminello lemon, namely ‘Zagara bianca’ and ‘2Kr’, grafted on sour orange and grown in pots. The compound was leaf sprayed three days before the inoculation by wounds with phialoconidia. Overall, disease index and disease progress curve in plants inoculated with P. tracheiphilus were reduced to a different extent by single leaf treatment. Additional post-inoculation treatments did not significantly affect the results. Quantification of DNA of P. tracheiphilus in leaf disks at the inoculation sites leads to conclude that the lessening of disease symptoms is not strictly related to a direct effect of the compound on the pathogen, and a host defence stimulation maybe involved.