Abstract
Manipulating or shifting annual grapevine growing cycle to offset limitations imposed by global warming is a must today, and delayed winter pruning is a tool to achieve it. However, no information is available about its physiological background, especially in relation to modifications in canopy phenology, demography and seasonal carbon budget. Mechanistic hypothesis underlying this work was that very late winter pruning (LWP) can achieve significant postponement of phenological stages so that ripening might occur in a cooler period and, concurrently, ripening potential can be improved due to higher efficiency and prolonged longevity of the canopy. Variability in the dynamics of the annual cycle was created in mature potted cv. Sangiovese grapevines subjected to either standard winter pruning (SWP) or late and very late winter pruning (LWP, VLWP) performed when apical shoots on the unpruned canes were at the stage of 2 and 7 unfolded leaves. Vegetative growth, phenology and canopy net CO2 exchange (NCER) were followed throughout the season. Despite LWP and VLWP induced a bud-burst delay of 17 and 31 days vs. SWP, the delay was fully offset at harvest for LWP and was reduced to 6 days in VLWP. LWP showed notably higher canopy efficiency as shorter time needed to reach maximum NCER/leaf area (22 days vs. 34 in SWP), highest maximum NCER/leaf area (+37% as compared to SWP) and higher NCER/leaf area rates from veraison to end of season. As a result, seasonal cumulated carbon in LWP was 17% higher than SWP. A negative functional relationship was also established between amount of leaf area removed at winter pruning and yield per vine and berry number per cluster. Although retarded winter pruning was not able to postpone late-season phenological stages under the warm conditions of this study, it showed a remarkable potential to limit yield while improving grape quality, thereby fostering the hypothesis that it could be used to replace time-consuming and costly cluster thinning. This preliminary study indicates that proper winter pruning date should be timed so as not to exceed the stage of two unfolded leaves.
Highlights
The relationship between leaf age and function in grapevine has been extensively studied in the past (Kriedemann, 1968; Poni et al, 1994; Patakas et al, 1997)
The same day acrotony was exhibited by the two-node standard winter pruning (SWP) spurs, the distal one having already reached the two unfolded leaf-stage and the proximal one still lagging at bud burst
Hypothesis that late or very late winter pruning (VLWP) applied after commencement of spring growth can consistently delay the whole annual growing cycle in the grapevine was partially confirmed
Summary
The relationship between leaf age and function in grapevine has been extensively studied in the past (Kriedemann, 1968; Poni et al, 1994; Patakas et al, 1997). Once the peak is reached, Pn rates thereafter usually start to decline at a rate depending upon environmental conditions, leaf exposure and source-to-sink balance (Chaumont et al, 1994). Working on Sangiovese vines grown without irrigation in the warm Po Valley, Poni et al (1994) found that at 4 months of age leaf Pn rates were halved compared to maximum rates reached at about 45 days; Schultz et al (1996) found that maximum Pn rates in Riesling vines grown in the cooler Rhine Valley stayed almost constant for approximately 3 months after reaching a peak at ∼30 days of age. When shoots are trimmed, the canopy abruptly “ages” since the youngest leaves are removed but lateral regrowth triggered by shoot cuts rejuvenates the canopy and, eventually, the newly formed lateral leaves can become an important source for ripening (Poni and Giachino, 2000)
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