Our paper offers unique information regarding the effects of DL-β-amino-n-butyric acid (BABA) on grape cluster compactness and Botrytis bunch rot development. The impact of treatment was investigated on a native Hungarian grapevine cultivar, 'Királyleányka' (Vitis vinifera L.) during three seasons. The highly sensitive cultivar with thin skinned berries provided excellent samples for Botrytis bunch rot studies. Our objective was to study if BABA treatment contributes to decrease Botrytis infection by promoting looser clusters. For this purpose, the female sterility effect of BABA in grapevine flowers was also examined, which may result in looser clusters. Cluster compactness was characterized with two different indexes; bunch rot incidence was assessed in percentages. Ovaries of flowers were examined under epifluorescent microscope. Significant differences were found in the compactness index (berry number/bunch length) between the control (2.87 ? 0.83 no./cm) and treated bunches in the case of 2.0 g?L-1 (2.18 ? 0.77 no./cm) and 3.0 g?L-1 (1.90 ? 0.72 no./cm) concentrations. Bunch rot incidence, however, was highly dependent on disease pressure influenced by the precipitation during ripening. In year 2013 all treatments gave significantly lower infection incidence, while the extremity of rain in 2012 and 2014, resulted in no epidemic or high infection, respectively. The treatment with 2.0 g?L-1 BABA concentration decreased cluster parameters and led to the lowest disease incidence. Microscopic studies proved that successful treatments on cluster structure can be traced back to the female sterility caused by BABA. Our results presented clear evidence for the effectiveness of BABA treatment on Botrytis bunch rot by promoting looser clusters.
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