Abstract
ABSTRACT: Prohexadione-calcium (ProCa) is a gibberellin biosynthesis inhibitor and the objective of this study was to evaluate the effect of ProCa on the downy mildew (DM) and Botrytis bunch rot (BBR) epidemiology, and the yield and technological and phenolic parameters of grape Merlot cultivar. Experiments were carried out in a commercial vineyard in São Joaquim Municipality/SC, Southern Brazil, during the 2017-2018 and 2018-2019 growing seasons. ProCa was applied at four doses and three phenological stages: A) 0 g ha−1 (control); B) 1000 g ha−1 (inflorescence fully developed); C) 500 + 500 g ha−1 (inflorescence fully developeted and full flowering); D) 500 + 500 + 500 g ha−1 (inflorescence fully developed, full flowering, and berries pea-sized). DM and BBR incidence and severity were quantified weekly from the first symptom appearance until harvest, and their epidemiology was compared according to: a) the beginning of symptom appearance; b) the time to reach the maximum disease incidence and severity; c) the maximum value of disease incidence and severity; d) the area under the disease progress curve. In general, there were significant differences in the ProCa doses for all epidemiologic parameters of DM and BBR compared with the control plot; however, there was no significant difference among the ProCa doses. The principal epidemiological variables that differentiated the effect of ProCa on the DM and BBR control were the Smax and AUSDPC. Some yield and technological and phenolic parameters were negatively affected by different doses of ProCa, but it was still a good option for DM and BBR control in highland region of southern Brazil during the 2017-2018 and 2018-2019 growing seasons.
Highlights
The balance between the vegetative and productive parts of the grape plant is crucial for the success of grape cropping and production with oenological quality (BRIGHENTI et al, 2011)
There were significant differences in the ProCa effect for all epidemiological parameters of downy mildew (DM) and Botrytis bunch rot (BBR) compared with the control plot; there was no significant difference among ProCa doses
There was a significant difference in the beginning of symptom appearance (BSA) among ProCa doses when compared with the control plot, with the dose of 1000 g ha−1 applied at inflorescence fully developed – BBCH 57, showing the lowest BSA for DM and BBR
Summary
The balance between the vegetative and productive parts of the grape plant is crucial for the success of grape cropping and production with oenological quality (BRIGHENTI et al, 2011). Vegetative growth is mainly influenced by the interaction between canopy and rootstock and characterized by the vigor balance (FELDBERG et al, 2007). The vegetative/productive imbalance negatively affects the composition, ripening, and phenolic compound content of the grape (DA SILVA et al, 2010). Several chemicals have been developed to regulate growth plant to reduce the vegetative/ productive imbalance, including Prohexadione-Calcium (ProCa) (PETRACEK et al, 2003). A current problem has been observed in the São Joaquim region, Santa Catarina State, Southern Brazil, is the association of the vigorous rootstocks Paulsen 1103 with a soil condition with organic matter of more than 8.1%, causing a negative effect of excess vigor of plants and low productivity due to the high concentration of gibberellin at plant growth points
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