Loose clustered vignoles clones reduce late season fruit rots

Abstract

Context and purpose of the study – ‘Vignoles’ is an aromatic, white-fruited wine grape variety valued by growers and wineries in the Eastern United States. Vignoles is grown in diverse locations in New York, Missouri, Indiana, Ohio, Pennsylvania, Illinois, Nebraska and Michigan. Consumers recognize and value the variety for its special wine quality.  However, Vignoles production is limited by its extremely compact clusters which increase the propensity to Botrytis cinerea bunch rot and to sour rot, frequently leading to significant crop losses and decrease in quality. In 2007 the USDA grape genetics research unit used mutation breeding to screen and produce ‘loose-clustered’ clones that would offer slightly reduced fertility, less compact clusters, and reduced severity of cluster rots. Selections were evaluated at two field locations. Compared to standard vignoles, they reduced cluster rot severity by ~30 to 94%, and reduced cluster weight by 25-33% over 5 growing seasons. 

Material and methods – Candidate clones were identified from 2000 vines produced from irradiated budwood by observing cluster compactness and rot susceptibility from 2011-2014. From these, plantings of 18 selections (USDA Agricultural Research Service farm at Cornell Agri-Tech, Geneva, NY) or 8 selections (Cornell Lake Erie Research and Extension Laboratory, Portland, NY) and the industry standard Vignoles (STANDARD) were established. Following establishment, incidence and severity of cluster rots (Botrytis and sour rot), cluster compactness, and cluster weight were evaluated over three growing seasons, from 2016-2018 (Geneva, NY) or 2018-2020 (Portland, NY).

Results – At Geneva, NY where 18 accessions + STANDARD were evaluated, Clone, Year, and Year x clone were all significant predictors of cluster rot severity (P<0.001). Means separation showed that 17 of 18 clones (2016, dry year), all 18 (2017, wetter) and 14 of 18 (2018, severely wet ripening season) had significantly lower disease severity than the standard clone. Percent reduction of disease severity ranged from 34-69% (2016), 34-71% (2017), and 16-90% (2018). Cluster compactness (weight per cm of rachis length) metrics showed that 9 of 18 (2016), 7 of 18 (2017) and 7 of 18 (2018) were significantly less compact (lower wt/cm of rachis) than the standard Vignoles.

Among the eight accessions planted at Portland, NY, incidence (proportion of clusters with fruit rots) was reduced by 11-88% (2018), 39-81% (2019) and 39-70% (2020) compared standard Vignoles. Severity (% of cluster area with fruit rots) was reduced by 30-94% (2018), 55-92% (2019) and 56-87% (2020), compared to the ~37-42% rot observed in the standard accession. At both sites, disease severity was correlated with cluster compactness at Portland, NY.

Yield and yield components were evaluated in 2019 only. Control vines had 8.6 kg/vine, while two selections (R65V83 and R67V79) averaged 6.2 and 6.8 kg/vine respectively – roughly  a~25% reduction in yield. Median cluster weights were 86 g/cluster (Standard Vignoles) versus 54.7 and 58.0 g/cluster in the R65V83 and R67V79 selections – approximately a 33% reduction in cluster weight. These two selections offer a 2 to four-fold reduction in disease severity, potentially offsetting the ~25% reduction in yield and quality losses from Botrytis and sour rot infections.