However, beyond these thresholds, flavonols started to degrade, and there was an indirect relationship between the flavonol content and the percentage of kaempferol for both cultivars, this relationship being significant only for Cabernet Sauvignon .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 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, low round pots 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. Correlation analysis between the monitored variables at harvest revealed a strong relationship between canopy architecture variables and berry flavonol content . Moreover, canopy porosity was strongly correlated to the kaempferol proportion in berry skins . On the other hand, a lower yield due to canopy management practices was related to decreased IBMP and increased flavonol content . Finally, a strong relationship was found between TSS and TA with the leaf to fruit ratio . Finally, a higher solar exposure estimated as the kaempferol proportion was strongly correlated with decreased anthocyanin berry contents and yield .Analysis of labor operations cost of canopy management practices indicated that the most expensive canopy management practices was the LRST where growers received a 53% lower income per hectare. Thereby, productivity data provided evidence that the cost of producing a kg of anthocyanin and removing a µg of IBMP was 10-fold greater in LRST compared to UNT per ha .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, 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 vineyardeither. 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, plastic pots 30 liters 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. During the experiment conducted in the 2019 growing season, the kaempferol proportion increased in LR and ST treatments, but largest increase was measured when ST and LR were applied concurrently. Likewise, the higher the degree of exposure degree a greater kaempferol accumulation was observed during the 2017 growing season. The increase in kaempferol in total proportion of flavonols was accompanied with a concomitant decrease of quercetin and myricetin proportions. These results are corroborated with our previous work performed on Merlot and Cabernet Sauvignon. , and by others on Cabernet Sauvignon, Nero d’Avola, Raboso Piave, and Sangiovese in Italy . We previously reported the proportion of kaempferol was a feasible tool for accounting the solar radiation received by berry due to the greater canopy porosity and this corresponded to the 1930 W·m−2 of global radiation accumulated at the research site in Experiment 3. On the other hand, the higher proportion of quercetin derivatives in detriment of myricetin derivatives found in LR vines has been related to down regulation of F3’5’H family genes . Previous work on red grapevine berries, indicated that IBMP content decreased with greater solar exposure due to the canopy management practices during berry ripening . In our work, the lowest IBMP content was measured in LRST berries. Our results indicated a negative and linear relationship between leaf to fruit ratio and IBMP content.
Conversely, the relationship between kaempferol proportion and IBMP was not significant. Therefore, our data suggested that the decrease of IBMP content was better explained by changes in the source-sink balance rather than differences in solar exposure. Likewise, Koch et al. provided evidence that solar exposure affected IBMP content to a greater extent when canopy porosity was enhanced before fruit set and not during berry ripening corroborating our results. The lower berry IBMP content was explained by a diminution of the accumulation rates rather than increased rates of degradation due to canopy management practices and restriction of applied water between fruit set and veraison in a warm climate.Vineyard-fl oor management strategies, such as weed control and cover-cropping, have wide-ranging impacts both inside the vineyard, in terms of crop management and productivity, and outside the vineyard, in terms of runoff and sediment movement into streams and rivers. The increasing importance of water-quality issues statewide, including in Monterey County where the Salinas River drains into the Monterey Bay National Marine Sanctuary, highlights the need for management strategies that limit environmental impacts. Growers are interested in alternative weed-control practices and cover crops, but they need information in order to balance benefits with the economic realities of wine-grape production. We established a 5-year experiment in a commercial vineyard in Monterey County with the intent of identifying effective practices that can be integrated into the cropping system without negatively affecting winegrape production. The vineyard floor consists of two zones: the rows, a 2- to 4-foot-wide swath underneath the vines, which are managed primarily to control weeds by herbicide applications or cultural practices ; and the middles, interspersed between the rows, which are vegetated by cover crops or resident vegetation in the dormant season, and are tilled or left untilled in spring. Growers manage weeds in rows to reduce competition for water, nutrients and light , and to prevent tall-statured weeds such as horse weed from growing or climbing into the canopy, where they interfere with harvest.