Issue link: http://winesandvines.uberflip.com/i/918844
January 2018 WINES&VINES 125 PRACTICAL WINERY & VINEYARD GRAPEGROWING To determine whether the effect of the flies was due to microorganisms that they contrib- uted or to some non-microbiological factor, colonies of axenic fruit flies were developed. These were reared in sterile media, rendering them devoid of gut and surface microbiota. In a series of similar inoculation experiments utilizing Red Globe grapes and multiple com- binations of microbes plus axenic fruit flies (or not), only the following microbial combina- tions (each consisting of a yeast and AAB spe- cies) consistently caused sour rot symptoms, and only in the presence of axenic flies: • Saccharomyces cerevisiae x Acetobacter aceti • Saccharomyces cerevisiae x Gluconobacter oxydans • Pichia kluyveri x Acetobacter aceti • Pichia kluyveri x Gluconobacter oxydans Three components essential for sour rot disease development The results show that three components are essential for sour rot disease development: Yeast, which first produce ethanol from the juice of affected grapes, Acetic acid bacteria, which convert this ethanol to acetic acid, Drosophila fruit flies, which contribute to the breakdown of infected berries and the liberation of acetic acid volatiles responsible for the characteristic vinegar smell. (Similar results were obtained in some parallel stud- ies comparing the effects of D. melanogaster, the common fruit fly, and D. suzukii, the spotted wing Drosophila, which is not a com- mon pest on grapes in North America). None of these elements cause disease symptoms on their own. In nature, yeast and acetic acid bacteria may originate from several sources: the outer surface of healthy berries (albeit in low numbers), inside healthy berries (vari- ous non-Saccharomyces yeasts such as Pichia spp. were repeatedly isolated from inside healthy berries obtained from vineyards in New York, California and Washington state, in addition to AAB on occasion) and Dro- sophila fruit flies. In addition to making a vital non-micro- bial contribution to sour rot development by facilitating their breakdown, fruit flies also vector the causal yeast and bacteria both on the outside of their bodies and by transfer- ring gut microbes during feeding, thereby spreading the disease rapidly once it has begun. Thus, sour rot control programs in the vineyard ideally should include measures targeting both the abovementioned microbes and fruit flies. 6-arm Kniffen Flat Cane VSP (or Guyot) Pendlebogen (VSP with arched canes) Lyre: view from 6-arm Kniffen Umbrella Kniffen Flat Cane VSP (or Guyot) High Wire Cordon Two-Tier Flat Bow Pendlebogen (VSP with arched canes) Lyre: view from end of row Lyre: view from GDC: view from end of row GDC: view from Current-year shoots rise from the fruiting-wire cane 3.5 feet above the ground and are maintained in a vertical position by the catch wires above. Source: Horticulture Section, School of Integrative Plant Science, Cornell University. HIGH-WIRE CORDON TRAINING SYSTEM Current-year shoots droop downward from their origin on the permanent cordon, 5.5 feet above the ground. VSP TRAINING SYSTEM