Suppression of Botrytis bunch rot in Chardonnay grapevines by induction of host resistance and fungal antagonism

A chemical elicitor, 5-chlorosalicylic acid (5CSA), and a fungal antagonist Ulocladium oudemansii, were evaluated for their ability to suppress Botrytis cinerea in Chardonnay grapes. Potted plants developed resistance to B. cinerea infection after treatment with 1 mM 5CSA. Resistance, as expressed by a reduction in lesion diameter, was greatest in plants that were treated with 5CSA 7 days before inoculation. This delayed response is indicative of induced resistance and this is supported by observations that 1 mM 5CSA did not significantly affect B. cinerea growth on amended media or on treated necrotic leaf disks. Compatibility studies on necrotic leaf disks demonstrated that 5CSA had no significant adverse effects on U. oudemansii conidial germination, germ tube vigour and B. cinerea suppression, indicating that these two components could be mixed for field use. Applications of 5CSA, U. oudemansii and 5CSA+U. oudemansii, every 10-14 days from flowering until one week pre-harvest significantly (P<0.05) reduced Botrytis bunch rot severity on Chardonnay grapevines. Disease severity at harvest was significantly lower on treated bunches than on untreated controls. There was no significant difference between stand-alone and combination treatments at vintage. Harvested bunches were incubated in high humidity chambers to encourage Botrytis bunch rot development. After 14 days incubation, Botrytis severity increased to 83% on untreated bunches compared with between 37-41% on those treated with 5CSA and U. oudemansii. Under these conditions 5CSA+U. oudemansii provided significantly better control than each component alone and reduced bunch rot severity to less than 15.2%. The potential deployment of elicitors and antagonists to control Botrytis bunch rot in grapes is discussed.