Relationship Between Cluster Compactness and Bunch Rot in Vignoles Grapes

Abstract

The impact of cluster compactness and debris retention on harvest bunch rot of Vitis interspecific hybrid ‘Vignoles’ was investigated between 2001 and 2005 near Lake Erie, in Pennsylvania. Cluster compactness was characterized subjectively based on the OIV code 204 standard and objectively by determining the number of berries per centimeter of rachis. In 2001, 2002, and 2004, the median number of berries per centimeter for loose clusters was 6.3, 7.0, and 6.4 compared with 10.2, 12.7, and 12.4 for the compact clusters, respectively. Kolmogorov-Smirnoff and the Mann-Whitney U two-samples tests confirmed that the distribution of the berries per centimeter was significantly (90 ≤ χ2 ≤ 184.3; P < 0.0001) different between the two subjective compactness categories. Cluster compactness was strongly correlated with bunch rot incidence (χ2 = 73.1 and 62.2 for 2001 and 2002, respectively; P < 0.0001), whereby disease incidence was higher in compact than in loose clusters. Logistic regression analysis indicated that every additional berry per centimeter unit of compactness almost doubled the likelihood of a cluster becoming infected with bunch rot (odds ratio = 1.828, 95% confidence interval [CI] = 1.392 to 2.399 in 2001 and odds ratio = 1.705, 95% CI = 1.394 to 2.085 in 2002). In 2004, bunch rot severity in compact clusters was nearly four times that of loose clusters. Linear regression analysis revealed that berries per centimeter accounted for >89% of the variation in bunch rot severity (R2 = 0.893, P < 0.0001, n = 30) and >74% in cluster weight (R2 = 0.745, P < 0.0001, n = 30). Accumulations of dehiscent floral debris contributed to greater bunch rot severity, and the effect was more pronounced in compact clusters than in loose clusters. Removal of basal leaves at trace bloom reduced berries per centimeter by 13% in 2004 and >25% in 2005, with corresponding reductions in bunch rot severity of 60% in 2004 and 62.5 to 82% in 2005. These results indicate that berries per centimeter is a good indicator of cluster compactness in Vignoles, and that practices that reduce cluster tightness would be effective in an integrated program for control of bunch rot on this cultivar.

Effect of Y-trellis and vertical shoot positioning training systems on downy mildew and botrytis bunch rot of grape in highlands of southern Brazil

“…A combination of frequent rain and sustained humidity, particularly in spring and summer, provided conditions for leaves and berries remain wet, enabling infections by P. viticola and B. cinerea. Previous studies have shown that for P. viticola, optimal growth is at temperatures of 20-25°C (Madden et al, 2000;Kennelly et al, 2005) and B. cinerea growth is optimal at 15-23°C (Wilcox, 2005;Hed et al, 2009).…”

Botrytis bunch rot on 'Sauvignon Blanc' grapevine on the Y-trellis and vertical shoot-positioned training systems

“…Any time after bloom, under high humidity, the floral debris will produce spores that can infect the rachis and other cluster parts. The initial symptoms of the disease occur in the internal tissues of the berry; the berry turns dark -which is easy to observe in a white variety like 'Sauvignon Blanc' -, the pulp softens, and the skin easily splits or slips off the pulp when touched (Hed et al, 2009). …”

“…Grape cultivars, such as Sauvignon Blanc, with dense canopies, thin skins, and/or compact clusters are more susceptible to botrytis bunch rot (Hed et al, 2009), since their ripening stage and harvest season coincide with the period of heavy rain (average of 195 mm per month) in Southern Brazil. According to Bem et al (2015), the vertical shoot-positioned training system, compared with the Y-trellis one, reduced botrytis bunch rot intensity in 'Cabernet Sauvignon' under the edafoclimatic conditions of the highlands of the state of Santa Catarina.…”

“…2017 DOI: 10.1590/S0100-204X2017000900015 the percentage of rotten berries per cluster. Cluster compactness was calculated as the ratio between the number of berries and the length of the rachis (cm) according to Hed et al (2009). For each plot, 30 random clusters were evaluated per training system (treatment).…”

“…For the 2013/2014 and 2014/2015 crop seasons, accumulated rainfall, average temperature, and relative (Hed et al, 2009). Botrytis bunch rot incidence and severity were significantly higher in the YT than in the VSP training system in the 2013/2014 crop season, because the climate conditions were favorable to B. cinerea infection and development (Table 1).…”