Inception, Diagnosis, and Consequences of the Berry Shrivel Disorder
“Berry shrivel” (BS) has been used to describe a post-veraison disorder of table and wine grapes, and we have determined that the hallmark symptom of this disorder is a low Brix in berries but a green and healthy appearing rachis. This disorder contrasts to bunchstem necrosis (BSN), in which berries also shrivel, but bunches exhibit a necrotic rachis, and berries may exhibit a high or a low Brix, depending on the timing of the necrosis. This research has demonstrated that sugar accumulation in BS-affected berries is substantially slowed or stopped approximately 2 weeks prior to the appearance of shriveling, and we have suggested that the term ˜sugar accumulation disorder” (SAD) be used to describe this condition. Based on reduced sugar accumulation as a key element of SAD, crop thinning experiments were carried out in Sauvignon Blanc, Grenache and Cabernet Sauvignon vineyards at a total of 7 locations, and in one location thinning gave a significant reduction in SAD incidence. In 2008 however, the level of SAD was generally very low, with many of the monitored Cabernet Sauvignon vineyards showing 0%SAD in all thinning treatments. At the Oakville Experimental Vineyard (OEV, Napa) we have shown that the Brix of non-symptomatic berries on SAD affected vines is also substantially below the Brix of normally-developing berries, indicating that SAD effects all of the fruit on an affected vine. However, in two other North Coast vineyards (Juliana, Jordan), non-symptomatic berries on SAD affected vines had normal Brix, so it is possible that there is more than one cause of SAD. For the SAD affected vines at OEV we have been able to propagate the disorder, indicating that the disorder is carried in the wood source, and a key finding in the 2008 season was preliminary evidence from a number of grafting studies that SAD can spread from a wood source bud to the rest of the vine. This was the first year to obtain fruit from these grafts however, and this result must be confirmed with further study.