## 4 Discussion
### Vegetative and Generative Development  
Despite the physiologically self-regulating bud burst mechanism in SMPH [20], growth of SMPH vines was elevated, due to a high bud load, resulting in more shoots. Hence, more bunches and a higher total leaf area per meter of row. This confirmed the results of previous studies under warm and moderate climate conditions [20; 22]. [PERSON] et al. [20] detected a lower bud burst rate in SMPH, ranging from 49% to 62% depending on canopy height, which is in agreement with our results. Sprayings with gibberellic acid led to decreased bud fertility, and consequently, less infloresances in minimal pruning trials of [PERSON] et al. [34]. Although a trend to a lower bud fertility (data not shown), a lower bud burst rate and less infloresances were observed in SMPH GA, we could not confirm these results statistically. Conversely, SMPH ST seemed to increase bud burst rate, but SMPH BT did not affect bud burst. Generally, the development of the total leaf area in SMPH was earlier, compared to VSP, due to the higher amount of shoots and wider distribution across the entire trellis system. This needs to be considered in the plant protection strategy, e.g., via an adaptation of the pesticide dose per ha, since the target leaf area and the total number of bunches were higher in SMPH, compared to VSP. SMPH showed a higher overall photosynthetic  
Figure 5: Total soluble solids (TSS) during ripening period (**A**) and at harvest (**B**) in relation to leaf area to fruit weight-ratio (cm\({}^{2}\) g\({}^{-1}\)) for cv. [PERSON] trained in Vertical Shoot Positioning (VSP *) and Semi-Minimal-Pruned Hedge (SMPH) with non-thinned control (SMPH \(\blacksquare\)), shoot thinning (SMPH ST \(\blacktriangledown\)), biotechnological thinning (SMPH GA \(\blacklozenge\)) and bunch thinning using a harvester (SMPH BT \(\blacktriangle\)) in the years 2017–2019. Error bars are representing \(\pm\)SD. capacity [20], and higher yield, which increased water consumption through transpiration. Since the risk of dry summers increase under future climate change scenarios [5], irrigation might be considered in SMPH as drought related leaf abscission was observed in 2018. Average total leaf area as well as leaf area per shoot was increased in SMPH BT in subsequent vintages, indicating that yield reduction by bunch thinning improved growth. Shoot thinning induced a growth compensation effect. While, total leaf area after shoot thinning was 20% to 32% lower, compared to SMPH in May 2018, and 2019 respectively, only marginal differences were detected in August (\(-2\%\) to \(-3\%\)). The observed growth compensation effect using SMPH ST increased primary shoot length, shoot diameter, bunch weight and leaf area per shoot, which is in accordance with findings of [PERSON] et al. [35]. The first trimming event drastically reduced total leaf area in SMPH with considerable effect on source-sink relation, i.e., LFR. Usually, a LFR of 16 to 22 cm\({}^{2}\) g\({}^{-1}\) is required to ripen grapes in cooler climates of Germany, whereas a LFR of 8-12 cm\({}^{2}\) g\({}^{-1}\) is appropriate for warmer climates [36]. Our results revealed, that LFRs obtained with SMPH (ranging from 11.8 to 15.2 cm\({}^{2}\) g\({}^{-1}\)) were sufficient to achieve the legal threshold of different wine categories of quality wine of origin for cv. Riesling at delayed harvest dates. In the trials of [PERSON] et al. [37], as in the present study, yield reduction elevated LFRs in all thinning treatments and accelerated maturity progress. Since SMPH ST reduced both, shoots, as well as infloresances, and bunch weight increased, the higher leaf area per shoot has contributed to an elevated LFR. We conclude that the delayed ripening in SMPH is predominantly caused by the reduction in leaves (source) as yield (sink) remained high in SMPH. These findings are in line with several authors [38; 39] who delayed ripening with different canopy sizes.