Interaction of perfused chemicals as inducers and reducers of bunchstem necrosis in grapevine bunches and the effects on the bunchstem concentrations of ammonium ion and abscisic acid

Wick-feeding of chemicals into grape bunches in the field successfully induced bunchstem necrosis (BSN) and hastened or delayed berry ripening. Evidence is presented that ammonium ion has a specific effect in delaying ripening. The most potent inducer of BSN was the amine agmatine; this compound, and the auxin benzothiazol-2-oxyacetic acid (BTOA), are new additions to the list of chemicals that induce BSN-like symptoms. Other inducers were ammonium sulfate, abscisic acid (ABA). Comparison of analyses of bunchstem tissue at two weeks after perfusion showed no correlation between released ammonium levels and BSN incidence. The potency of agmatine, which increased both ammonium and BSN, may be due to its effect in releasing the polyamine putrescine which is potentially phytotoxic. Positive correlations were evident between extracted levels of ABA and BSN incidence since most perfusions that induced BSN caused an increase in ABA. Co-perfusion of calcium and magnesium salts did not significantly reduce the incidence of induced BSN, a result that accords with previous vine-spraying experiments.