It can occur in many varieties, but is especially prevalent in Cabernet Sauvignon on California’s North Coast. It has been described in the literature in many different countries, with descriptive terms that include waterberry , bunchstem dieback , shanking , stiellähme , palo negro , desséchement de la rafl e and dessichimiento della rachide . No specifi c cause of bunchstem necrosis has been identified, despite many years of research. In some cases, varietal differences in susceptibility have been correlated to xylem structure, specifi cally a reduction on the area of xylem distal to branch points in the peduncle . The incidence of bunchstem necrosis has also been correlated to various concentrations or ratios of mineral nutrients, including magnesium, calcium, potassium and nitrogen . Work in Chile and Australia has shown that the amino acid metabolite putrescine is associated with bunchstem necrosis. More light in the canopy can also reduce bunchstem necrosis . Bunchstem necrosis can appear very early in fruit development or after veraison. The terms “inflorescence necrosis” and “early bunchstem necrosis” have been used to describe bunchstem necrosis around bloom . The composition of such fruit varies depending on when during fruit development the rachis becomes necrotic.

Presumably, the necrosis prevents both sugar and water transport to the berry. Hence, if the rachis becomes necrotic early in the ripening period before the berry has accumulated much sugar, container size for blueberries fruit will have low Brix . On the other hand, if the rachis becomes necrotic after the berries have accumulated appreciable sugar, subsequent shriveling can concentrate the sugars. Bunchstem necrosis in Cabernet Sauvignon on the North Coast is usually the latter type. Fruit with bunchstem necrosis can have a Brix as high as 42 .Another disorder with symptoms that occur during the ripening period has been called “berry shrivel”; we recently proposed that it be called “sugar accumulation disorder” . This disorder was first described in Emperor table grapes from California’s San Joaquin Valley and is characterized by poor coloration and low sugar accumulation. Sugar accumulation disorder has been found in a number of varieties and is present in many areas of California. In general, it affects only a small proportion of clusters in a vineyard, though in certain years and vineyards up to 50% of the fruit can be affected. Regardless of the variety or location, fruit affected by sugar accumulation disorder has lower pH, berry weight and Brix compared with normally developing fruit . When multiple rachises and fruit with sugar accumulation disorder were tested for minerals, the only consistent difference from normally developing fruit or rachises was increased calcium in the rachis tissue . To test the hypothesis that fruit exhibiting sugar accumulation disorder may have altered nitrogen metabolism, we measured the amounts of nitrogenous compounds at harvest in fruit with the disorder compared to normally developing fruit.

The vines were located at the UC Oakville Experimental Vineyard in the Napa Valley. Samples were taken at harvest on Oct. 21, 2005. Berries with sugar accumulation disorder came from clusters on six vines that historically exhibited the disorder and showed symptoms in 2005 . Normally developing berries came from clusters on three nearby vines that had no history of sugar accumulation disorder and did not display symptoms at harvest. Two berries were sampled from each cluster and eight to 10 berries were pooled to ensure enough material for analysis. Berries were peeled, their seeds removed and flesh homogenized. One milliliter of the homogenate was used for the analysis of nitrogenous compounds. Individual amino acids in three samples of berries with sugar accumulation disorder and normally developing berries were measured at the UC Davis Molecular Structure Facility . Briefly, juice samples were acidified with sulfosalicylic acid to precipitate any intact protein before analysis. Free amino acids were separated using a Li-citrate buffer system with ion exchange chromatography on a Hitachi L-8900 amino acid analyzer. Amino acids were quantified by a postcolumn ninhydrin-reaction detection system. Amino acid concentrations were quantified from peak areas using standard curves. Data was analyzed by ANOVA . Means comparisons were by Dunnett’s test at P = 0.01. Fruit with sugar accumulation disorder from the Oakville Experimental Vineyard had significant differences in many nitrogenous compounds compared to normally developing fruit . The concentrations of some nitrogenous compounds increased while others decreased, yet the overall amount of nitrogen per berry did not significantly differ.

In addition to carbohydrate metabolism, nitrogen metabolism in fruit with sugar accumulation disorder was affected, although there was no net reduction in nitrogen import. The large increase in ammonium in fruit with sugar accumulation disorder suggests interference with transamination or ammonium assimilation processes . Excess ammonium is toxic, and might account for the increased cell death observed in berries with sugar accumulation disorder compared to normally developing fruit . The reduction in phenylalanine in fruit with sugar accumulation disorder may explain its poor coloration, as phenylalanine is a necessary component for the biosynthesis of anthocyanins . Likewise, an increase in the amino acid hydroxyproline may indicate a stress response. It remains unclear what changes in metabolism are leading to these observed differences in other nitrogenous compounds, but the fact that these differences exist suggests that both nitrogen and carbohydrate metabolism are affected by sugar accumulation disorder.Sugar accumulation disorder and bunchstem necrosis are often confused with one another due to the similar appearance of affected fruit. With sugar accumulation disorder, the rachis appears outwardly healthy with no signs of necrosis. These two disorders can usually be differentiated by berry composition as well. As noted, berries affected by sugar accumulation disorder have lower Brix compared to normally developing fruit, whereas berries with bunchstem necrosis may have low to unusually high Brix depending on when in development the rachis becomes necrotic. The differences can often be large enough to distinguish by taste . In fact, fruit with sugar accumulation disorder stops accumulating sugar several weeks before shriveling symptoms become visible . In contrast to the shrivel of bunchstem necrosis, which can appear any time after veraison, the shrivel symptoms of sugar accumulation disorder usually appear late in ripening, several weeks to just days prior to harvest. Given these distinguishing characteristics, we suggest that the terms “sugar accumulation disorder” and “bunchstem necrosis” be adopted instead of “berry shrivel” and “waterberry,” which only describe fruit appearance/flavor.Within perennial crops, the grapevine is the most economically important fruit crop with more than 7.4 million cultivated hectares worldwide in 2016 . Many of the viticulture areas of the world rely on irrigation for consistent production . In the last decades, there is an increasing need for irrigation within the traditionally non-irrigated regions due to the current permanent rise in global air temperature and higher evapotranspiration with no appreciable gain in precipitation . Furthermore, the majority of viticultural regions are forecasted to experience a reduction in cloud coverage and rainfall and an increase in solar radiation reaching the earth’s surface , leading to higher temperatures and, consequently, higher evaporation from soils. Micro-irrigation strategies aim to replace frequently just the amount of water to meet the actual crop evapotranspiration demand in the immediacy of the root zone without using the storage capacity of the soil . Irrigation of vineyards usually introduces a predetermined water deficit. Therefore, raspberry grow in pots deficit irrigation has emerged as a potential strategy to allow grapevine to withstand water shortage during the growing season without yield loss and maintaining the berry composition .

Severe restrictions of water availability may accelerate sugar accumulation in grape berry in hot climates and result in adverse effects on yield , fruit composition , or wine composition . However, a sustained moderate water deficit may improve canopy microclimate, increase water use efficiency, control vigor, and reduce berry size improving berry quality by means of enhancement of sugars and flavonoids in red wine grape . Nevertheless, the final berry composition and consequent wine quality are highly dependent upon the proper control of carbohydrate partitioning, which balance the growth and metabolism of the source:sink organs . Non-structural carbohydrates are responsible for providing energy and carbon for grapevine growth, being stored as reserves in grapevine perennial organs. The role of stored NSC in the early season is crucial until bloom when leaf photosynthesis becomes the primary source of carbon . The capacity of grapevines for replenishing these carbohydrate reserves increases at mid-ripening . In addition, sugars directly or indirectly control a wide range of physiological processes, including photosynthesis, sugar transport itself, nitrogen uptake, defense reactions, secondary metabolism, and hormonal balance . Not only sugar transport and partitioning play key roles in the regulation of plant development, but also they influence how grapevines respond to biotic and abiotic stress factors . NSC storage may be altered by both abiotic factors and internal competition for carbon in grapevine, and in turn, this may modify grapevine growth, yield, and berry chemistry . Therefore, to ensure sufficient vegetative growth, yields, and acclimation to environmental stresses, grapevines must efficiently allocate available annual resources to both vegetative and reproductive tissues. Increased soil temperature due to the changing climate, especially before veraison, strongly affects seasonal balance between shoot and root growth, bloom, plant water use, photosynthesis, and the availability of carbohydrate reserves . Water availability is a determining factor for cell growth and photosynthesis and for the redistribution of carbohydrates between the source and sink organs . Indeed, shifting in root to shoot growth in response to external resource availability allows plants to minimize some critical resource limitations . However, our understanding of the factors determining carbon allocation among the different organs remains limited. Additionally, the incidence of water deficits is particularly acute during fruit development, when there is a great competition for photo assimilates among newly established sinks such as flowers, seeds, lateral shoots, and fruit and permanent structures such as trunks, stems, and roots . The objective of this study was to characterize the primary metabolism response of grapevines to different applied water amounts based on the replacement of fractions of ETc on grapevine physiology, as well as to assess their effect on carbon partitioning among the source and sink organs during two growing seasons.At harvest, 60 berries per treatment-replicate were randomly collected and weighed to determine berry mass. Then, in the 2019–2020 season, these berries were crushed for must sugar determination. Total leaf area was calculated by defoliating one grapevine per treatment-replicate after harvest and using the regressive relationship between leaf dry mass and leaf area. A subsample of oven dried leaves from each treatment-replicate was collected for sugar and starch analysis. Then, leaf area to fruit ratio was calculated by dividing the leaf area by the yield per vine and reported as m2 /kg. Six weeks following the harvest of 2020 , one grapevine per treatment-replicate was removed from the vineyard by using a mechanical spade. The grapevine was then portioned into trunk and cordon, roots, and stems . Then, each portion was weighed on a top-loading balance to obtain the fresh biomass of the portions. A subsample of shoots and fine roots was collected for organ-dried biomass estimation and sugar and starch analysis. Harvest index was calculated after oven drying the samples.Subsamples of leaves, shoots, and roots were oven-dried at 70◦C to a constant weight. Dried tissues were ground with a tissue lyser . Thirty milligrams of the resultant powder was extracted in ethanol:water solution. Briefly, 1.5 ml was added to each sample and extracted for 10 min at 90◦C in a water bath. Then, they were centrifuged at 10,000 rpm for a minute, and the supernatant was collected for sugar determination. The procedure was then repeated for starch determination in which the resultant pellet was used. Total soluble sugars and individual sugars were determined in the shoot, leaf, and root ethanolic extracts and in the diluted berry must samples . Samples were filtered with PTFE membrane filters and transferred into high-performance liquid chromatography vials and subjected to reversed-phase HPLC analysis. The equipment consisted of an Agilent 1100 system coupled to a diode array detector and an Infinity Refractive Index Detector . The reversed-phase column was Luna Omega Sugar with a guard column of 5 mm. The temperature of the column compartment was maintained at 40◦C and the RID flow cell was kept at 35◦C.