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Etiology and Management of Sour Rot in Grapes
Megan Hall: Cornell University; Gregory Loeb: Cornell Univ; Wayne Wilcox: Cornell Univ
<div><span face="Calibri" style="font-family:Calibri;"><span size="3">Sour rot is a disease complex affecting grape growers and winemakers worldwide, characterized by the oxidation of the berry skin, internal development of acetic acid and partnered with the presence of <i>Drosophila </i></span><span size="3">fruit flies. We have shown that acetic acid production requires yeast to produce ethanol and bacteria to subsequently convert the ethanol to acetic acid through an oxidation reaction. We have characterized the microorganisms involved, determining that several yeast species (</span><i><span size="3">Saccharomyces </span></i><span size="3">spp., </span><i><span size="3">Hanseniaspora </span></i><span size="3">spp., and </span><i><span size="3">Pichia </span></i><span size="3">spp.) partnered with acetic acid bacteria (</span><i><span size="3">Gluconobacter </span></i><span size="3">spp. and </span><i><span size="3">Acetobacter </span></i><span size="3">spp.) can cause this reaction, but only in the presence of </span><i><span size="3">Drosophila </span></i><span size="3">spp. To investigate potential non-microbial contributions of </span><i><span size="3">Drosophila </span></i><span size="3">spp. to the complex, we produced axenic </span><i><span size="3">D. melanogaster </span></i><span size="3">eggs and reared larvae until axenic conditions, yielding adults devoid of gut or surface microbiota. Wounded berries exposed to the wild type flies for 8 days produced typical sour rot symptoms, but in order for symptom development to occur in those in the presence of axenic flies, co-inoculation with a yeast and acetic acid bacteria was required. In field trials conducted on cv. 'Vignoles' in 2013-16, both insecticide and antimicrobial treatments significantly reduced sour rot development. In 2015, untreated vines averaged 20.5% sour rot severity, and this was reduced by 73-81% on vines treated prophylactically post-veraison with weekly sprays containing a combination of the insecticide zeta-cypermethrin plus the antimicrobial potassium metabisulfite or hydrogen dioxide; severity was reduced by 49% on vines receiving only insecticide sprays. These trials further support the hypothesis that sour rot results from a complex of yeast, bacteria, and </span><i><span size="3">Drosophila</span></i><span size="3"> spp. and that targeting these organisms can provide significant levels of control.</span></span></div>

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