Quality differences of berries at different-heights on vinegrapes under vertical independent long-stem training system

Abstract:【Objective】In order to evaluate the vertical independent long-stem training system(VILSP) ap-plied extensively in Ningxia Hui Autonomous Region of China, the quality of berries at various- heights onthe vines under vertical independent long-stem training system were investigated. VILSP is a traditionaltraining system that is used extensively in wine grape cultivation in the Ningxia Hui Autonomous Region ofChina. It is characterized by extending a single vertical stem from the ground to the head catch wires with-out any outer arms and retaining a shoot every 15-20 cm along the cane as bearing wood. All of bearingwoods are subjected to spur-pruning to guarantee that the trellis system is stable. For many years, VILSPhas been the predominant pruning system in Ningxia because it is adaptable to high- density planting,which maintains adequate yields, as well as the use of mechanical pruners and harvesters. However, thefruiting-zones are positioned at different heights along the vines under VILSP, that range from 40 cm to200 cm above the ground. Thus, different grape berries on a single vine may be subject to different light mi-croclimates. Eventually, the quality of berries under VILSP might be influenced. Ningxia Hui AutonomousRegion is one of the important wine-producing regions of China. VILSP has been used in this region due tothe influence of tradition. Therefore, it is meaningful to evaluate VILSP. This study would advance our un-derstanding of grape training systems and offer instructive advices for the development of grape industry inNingxia Hui Autonomous Region.【Methods】Based on the fruiting characteristics of the selected grape va-rieties(Vitis vinifera L.‘Merlot',‘Cabernet Sauvignon'and‘Chardonnay') under VILSP, the heights offruiting-zones were classified as follows: up, 140-200 cm above the ground; middle, 80-140 cm; bottom,20-80 cm. Berries from the 3 heights of each vine were sampled separately. To evaluate the quality of ber-ries from different height, we measured the berry weight, cluster weight, soluble solids, reducing sugar, to-tal acids, nonanthocyanin phenolic and monomeric anthocyanin. Soluble solids were measured using TD-45 digital refractometer. Reducing sugar was determined with Fehling reagent and total acids were deter-mined with sodium hydroxide titration. Nonanthocyanin phenolic and monomeric anthocyanin were deter-mined based on HPLC-MS. All of the analyses were conducted in triplicate. One-way analysis of variance(ANOVA) was used to analyze the differences of berries at various-heights in berry weight, cluster weight,soluble solids, reducing sugar, total acids, nonanthocyanin phenolic, monomeric anthocyanin. Additional-ly, berry weight and cluster weight were grouped into yield factor; soluble solids, reducing sugar, total ac-ids and nonanthocyanin phenolic were grouped into quality factor; monomeric anthocyanin was grouped in-to color factor. Principal component analysis(PCA), which was conducted on a correlation matrix, was usedto analyze the 7 quality indicators for the evaluation of the differences of berries at various-heights.【Re-sults】In VILSP, the quality of berries at different-heights on the vines showed significant differences. TheANOVA results demonstrated that the top fruiting- zones of‘Merlot'berries showed significantly(P≤0.05) heavier berry weight and cluster weight, and for‘Cabernet Sauvignon'and‘Chardonnay', the signif-icantly heavier berry weight and cluster weight occurred in the middle fruiting-zones. For the 3 grape culti-vars, berries from the top and middle fruiting-zones had remarkably higher soluble solids and reducingsugar. As expected, the bottom berries of the 3 varieties had significantly low total acidity. Five nonantho-cyanin phenolics including flavanols, flavonols, benzoic acid, stilbenes and cionnamic acids were detectedin the grape berries. The top height berries from‘Merlot'and‘Chardonnay'were found significantly highcontents of all nonanthocyanin phenolics except stilbenes. For‘Cabernet Sauvignon', the berries of the topfruiting-zones presented dramatically high concentrations of all nonanthocyanin phenolics except benzoicacid. 9 types of basic individual anthocyanin were detected in the‘Merlot'and‘Cabernet Sauvignon',and no anthocyanin was detected in the white variety ‘(Chardonnay'). For‘Merlot', the berries from thetop fruiting-zones exhibited significantly high contents of all the anthocyanins except peonidin-3-O-glu-coside. For‘Cabernet Sauvignon', the berries from middle fruit-zones had remarkably high concentrationof all the anthocyanin. The yield(berry weight and cluster weight) of middle fruit-zones was higher thanthat of other fruiting-zones in‘Cabernet Sauvignon'and‘Chardonnay', but in‘Merlot', the top fruiting-zones had the highest yield. In the aspect of quality factor(soluble solids, reducing sugar, total acids andnonanthocyanin phenolic), the quality of berries from the top fruiting-zones of‘Merlot'and‘CabernetSauvignon'was superior to the other fruiting-zones, but for‘Chardonnay', berries from the middle fruit-ing-zone were superior. In the aspect of color factor(monomeric anthocyanin), berries from the top fruit-ing-zones of‘Merlot'possessed the best, but for‘Cabernet Sauvignon', the middle-height berries hadthe best colour. The PCA results showed that berries from different heights were located in different quad-rants of the PC1-PC2 plane, suggesting a high degree of difference in the quality of berries from variousheight fruiting-zones under VILSP. The quality of berries at different-heights was subjected to generalevaluation using PCA methods. The results indicated that for‘Merlot'and‘Cabernet Sauvignon', berriesfrom the top fruiting-zones had the highest score, suggesting the quality of berries from the top fruiting-zones was superior. But for the‘Chardonnay', the middle-height berries got the highest score, which indi-cated the middle fruiting-zone berries were superior. For the 3 varieties, the berries from the bottom fruiting-zones all got negative score, suggesting the quality of berries from the bottom fruiting-zones was worse under VILSP.【Conclusion】In VILSP, the quality of berries at different-heights on the vine showed significant differences. In particular, the quality of the berries from the bottom fruiting-zones get worse. Therefore, VILSP might not be a suitable training system for winegrapes. This training system should be improved to maintain consistent-height fruiting-zone for the quality control.