BIOLOGICAL ASSAYS TO STUDY INDUCTION OF RESISTANCE IN PLATANUS x ACERIFOLIA TO CERATOCYSTIS FIMBRIATA
M. Pilotti, S. Festa, F. Gervasi, R. Coppola
A study was undertaken on Platanus ´ acerifolia to assess the potential of wounding, salicylic acid, jasmonic acid, the ethylene precursor 1-aminocyclopropane-1- carboxylic acid, and the pharmacological inhibitors antimycin and norbornadiene, to induce local resistance to Ceratocystis fimbriata f.sp. platani, the agent of canker stain. In vitro studies were used to determine fungitoxicity and phytotoxicity of the chemicals. Fungitoxicity was characterized by fungal growth and germination of conidia on media supplemented with the chemicals. Results from these experiments indicate a role of salycilic acid and ethylene in promoting C. fimbriata conidia germination. Treatments of detached branches and leaf discs with the chemicals were used to determine nonphytotoxic concentrations for the experiments of resistance induction. Leaf and wood disc assays were developed for measuring the induction of resistance. In these assays, pretreatment with the chemicals caused a reduction of disease severity and of fungal growth, respectively, with the exception of jasmonate, which enhanced disease severity, compared to the 48 h wounding/water control. In leaf and wood disc experiments, wounding reduced disease severity and mycelium growth respectively. The fungitoxic effects of inducers and the possibility that a genuine induction of resistance could be triggered in the assays are discussed.