In vineyard production systems, canopy management practices are usually employed to control the source-sink balance and improve the cluster microclimate leading to an improved grape composition and resultant wines . Additional canopy management practices may be applied during berry development. Fruit-zone leaf removal and especially, shoot thinning have been widely used in order to increase the cluster exposure to solar radiation, reduce crop load as well as decreasing the pest pressures , increasing flavonoid content and diminishing herbaceous aromas . Nevertheless, when high air temperature and excessive radiation combine, detrimental effects on berry acidity and flavonoid content have been reported in warm climate regions . Leaf removal consists of removing basal leaves around the clusters in the east or north side during grape development increasing the cluster exposure to solar radiation. It is well known that an early leaf removal increased total soluble solids, anthocyanins, and flavonols . However, some authors reported increases in titratable acidity in Sangiovese and Teran cultivars while other authors found decreases in acidity with basal leaf removal on Tempranillo . Conversely, Sivilotti et al. reported a positive effect of leaf removal applied after flowering on Merlot grapevine by improving cluster integrity by reducing incidence of Botrytis, and lower herbaceous aromas without affecting yield and cluster mass. Contrariwise, Pastore et al. reported that defoliation at veraison reduced the anthocyanin content and increased the impact of sunburn. In fact, these authors found that leaf removal induced a general delay in the transcriptional ripening program, dutch buckets for sale which was particularly apparent for structural and regulatory genes involved in the anthocyanin biosynthesis.

Clearly, vineyard location, cultivar , timing of leaf removal , method , and degree of leaf removal , the growing season , among others, are all factors influencing how leaf removal affects grapevine berry composition and integrity. On the other hand, shoot thinning has been related to increased cluster and berry mass and the number of berries per cluster, with a reduction on yield . Conversely, Wang et al. observed that shoot thinning had relatively minor impacts on yield components because of a compensatory effect due to the lower cluster number with concomitant increase in cluster mass. Contrarily, shoot thinning practices on grapevine did not show a great impact on berry primary metabolism , however, secondary metabolites were affected by them . In fact, we recently reported an increase of two-fold in the flavonol content of Merlot berries when leaf or shoot removal was applied mainly by increasing the proportion of quercetin and kaempferol derivatives in detriment of the myricetin derivatives . Berry composition is dependent on a complex balance between compounds derived from primary and secondary metabolism. Between secondary metabolites, flavonoids play an important role in the quality and the antioxidant properties of grapes and are very responsive to environmental factors such as solar exposure . Anthocyanin compounds are responsive of the berry color, and flavonols act as a UV shields, contribute to the wine antioxidant capacity, color stability, and hue through copigmentation with anthocyanins . On the other hand, the methoxypyrazines are wine key odorants contributing to their herbaceous characteristics and have been related to unripe berries and poor-quality wines when these are not part of the wine typicity . Since they can be present in grape berry and wines at high levels, they may have an important sensorial impact on wine quality . Among methoxypyrazines, the 3-isobutyl-2- methoxypyrazine is considered the most relevant to wine flavor due to its correlation with the intensity of the bell pepper character of wines and its content at harvest seems to be dependent of the solar exposure .

The differences found in the literature about the effect of manipulating the canopy architecture on the flavonoid and aromatic content due to different solar exposure of berries in warm climates opens an important field of research. Therefore, we aimed to find the optimal ranges of berry solar exposure estimated as percent of kaempferol for flavonoid synthesis up regulation and the thresholds for their degradation, and to evaluate how canopy management practices such as leaf removal, shoot thinning and a combination of both affect the grapevine yield components, berry composition, flavonoid profile, and herbaceous aromas.The weather conditions during the execution of this experiment were highlighted by greater maximum daily temperatures when compared to the reference period . This was more prominent during the driest months . Moreover, global solar radiation received at the experimental site was to ca. 200 W m−2 greater than the total solar radiation recorded within the reference period . The LR and ST decreased leaf area index and increased canopy porosity. The combinatory effect of LR and LT treatments caused a 58% reduction of LAI and a 45% increase of canopy porosity . However, neither leaf area nor pruning mass showed significant differences between treatments. On the other hand, yield components were mostly affected by the shoot thinning treatments . Thus, shoot thinned vines showed lower number of clusters, yield, and Ravaz Index , and increased leaf area to fruit ratio per vine as expected. The extent of yield reductions was 55% and 47% for ST and LRST vines, respectively . Berry mass was not significantly affected by canopy management practices during the berry ripening although vines subjected to LRST tended to result in smaller berries . The most influential effects observed on berrychemistry were due to shoot thinning treatments . Therefore, shoot thinned vines had greater total soluble solids and lower titratable acidity from mid-ripening to harvest. However, no significant effect was observed on the must pH . Shoot thinned grapevines had higher anthocyanin content at veraison . However, we did not measure any changes to anthocyanin content at harvest as affected by the canopy management practices applied.

Although anthocyanin content was not affected, anthocyanin composition was modified by treatments from mid-ripening to harvest . Berry skins of ST and LRST grapevines showed a lower 3’4’5’/3’4′ ratio leading to increased proportion of cyanidins and peonidins in detriment of malvidins which was the most abundant anthocyanin found in berry skins . During the monitored period, different canopy management practices modified berry flavonol content . The berries from LRST grapevines showed the greatest berry skin flavonol content, while, at harvest, the flavonol content of LR, ST, and LRST was similar and greater when compared to the UNT content. Not only canopy management practices modified flavonol content but they also affected their composition. The LRST treatment had a higher proportion of kaempferol and quercetin from midripening to harvest and lower of proportion of myricetin after veraison . As expected, berry IBMP content decreased throughout ripening with all the canopy management practices tested in this study . However, we found the significant differences among treatments after veraison and at harvest. The LRST treatment resulted in the lowest IBMP content from mid-ripening to harvest.Yield components were mainly affected by shoot thinning practices, decreasing the number of clusters and yield per vine leading to unbalanced vines according to the previous studies . Yield per meter of row is increased quasilinearly with the increase in shoot density per meter of row as indicated by previous studies . The lack of effect of LR on yield was corroborated by several studies when a late leaf removal was applied. Moreover, Yu et al. and Cook et al. reported that grapevines may produce more leaves than required, especially in warm climates, therefore, the increase in canopy gaps and the diminution of external leaf layers did not elicit decreases in yield as they were not severe enough reductions to the functional leaf area. The RI between 5 and 10 is considered optimum for vine balance . Therefore, RI and leaf area to fruit ratio data reported with the grapevines subjected to shoot thinning were under cropped that led to lower yields. In our study, Cabernet Sauvignon vines were not able to modulate their vegetative biomass in response to canopy management practices applied. Previous studies showed that pruning mass values up to 1 kg/m of row were considered optimal under warm climate . In our experiment the pruning mass per meter of all treatments ranged from 0.5 to 0.7 kg/m without differences between treatments. Moreover, although the shoot counts were obviously different between treatments, we did not find differences in the pruning mass, that suggested lower lateral expansion and/or reduced shoot diameter with an increasing number of shoots as previously reported Brillante et al. . Consequently, we found that the mass of each shoot ranged from 28 and 25 g in UNT and LR, respectively, to 45 and 42 g in ST and LRST, respectively, hydroponic net pots corroborating work by Brillante et al. .Martınez-Lüscher et al. reported negligible variation of berry mass of Cabernet Sauvignon due to higher solar exposure under irrigated viticulture. Similarly, berry masses remained unaffected by a higher solar exposure of the cluster due to canopy management practices unless they were directly exposed to sunlight where berries may suffer dehydration as previously reported by Mijowska et al. . This has been attributed to the effect of the higher temperatures with subsequent increases in berry transpiration that affected cell division and elongation . Under our experimental conditions, shoot thinning treatments hastened berry ripening by enhancing the TSS to ca. 2.5°Brix and decreasing must titratable acidity by 0.6 g•L−1 at harvest.

Thus, overexposure has been related with higher pH due to the elevated temperature that berries overcome and the subsequent organic acid degradation . Nevertheless, Wang et al. recently suggested that changes on the source-to-sink ratio induced by shoot thinning might have more influence on berry maturity than the change in the microclimate they reported.Cultural practices have been related to increased anthocyanin content . However, in agreement with other studies , under our experimental conditions, berry anthocyanin content did not increase due to LR, ST or LRST. Similarly, anthocyanin content was not affected by mildexposure in berries collected from the commercial vineyard either. Increasing exposure was detrimental for anthocyanin content as the overexposed berries were subjected to higher temperatures that may have impaired their accumulation . The anthocyanin berry content at harvest is the result between synthesis and degradation rates. It was reported anthocyanin synthesis may be up-regulated by greater exposure . Therefore, ST and LRST increased the anthocyanin content at mid-ripening because of the increasing solar exposure . Additionally, it was recently highlighted that some members of the dihydroflavonol reductase and UFGT genes required for anthocyanin biosynthesis were moderately up-regulated in LR treated berries leading to increases of anthocyanin content at mid-ripening . However, at harvest, no significant effect of canopy management practices on anthocyanin content was found, and this result is corroborated by Pastore et al. who reported no beneficial effect due to higher cluster exposure in warm climates. Although cultural practices may induce different cluster temperatures by increasing exposure, we did not find a clear relationship between exposure and cluster temperature when kaempferol proportion are low suggesting that results of this work were mainly explained by different exposures. Nevertheless, under elevated temperatures, a down-regulation of anthocyanin biosynthesis and enhanced rates of degradation have beenreported . Those authors suggested that high temperature induced anthocyanin degradation by enhancing the expression of VviPrx31 and consequently the peroxidase activity. Likewise, overexposed berries with kaempferol proportions greater than 10% were subjected to higher temperatures that dramatically decreased anthocyanin content. Matus et al. reported that flavonol content increased by two-fold in exposed berries compared to non-exposed. Our results corroborated this finding partially, depending on the level and duration of exposure, canopy position of the berries, and orientation of the vineyard. Therefore, when flavonol proportion was below 10% of kaempferol, flavonol content increased; but would decrease after this inflection point due to degradation. Matus et al. further indicated that this increase in flavonol may be driven by the up-regulation of MYB12 and flavonols synthase 4 due to the greater exposure suggesting that FLS4 could be a target of MYB12 in grapevine. Accordingly, Sun et al. found that increased accumulation of flavonols in light exposure berries, were accompanied by the up-regulation of several genes of the FLS gene family suggesting that they may be functionally redundant in response to light signal.