By increasing fruit exposure to sunlight and influencing fruit development, leaf thinning in the fruit zone can improve grape quality and lower disease incidence; however, further investigations on the timing, varietal response and intensity are needed to optimize results and to better understand underlying physiologic responses. Fruit zone leaf thinning was applied at different timing and intensities to evaluate its effect on cluster health and fruit composition in Cabernet Sauvignon and Chardonnay. Treatments consisted of control (C), pre-bloom leaf thinning (PB) and two levels of fruit-set leaf thinning (three leaves, PF3 and six leaves, PF6). In an additional project on Cabernet Sauvignon, two levels of hedging (17th node, NH and 12th node, H) were integrated with no leaf thinning (L) and fruit set leaf thinning (LR, three leaves).
All leaf thinning treatments consistently reduced disease incidence compared to control vines in both varieties, with the reduction extent varying between 2017 and 2018. Yield was not negatively affected by leaf thinning treatments, even though PB reduced cluster compactness by decreasing the number of berries per cluster of Chardonnay in 2017. Control vines tended to have greater titratable acidity than defoliated vines, while Brix and pH responses varied between seasons. No direct positive correlation was found between sunlight exposure and norisoprenoids concentration. Post fruit set leaf thinning PF6 consistently increase free norisoprenoids at harvest, while pre-bloom defoliation never did. Heterogeneous responses were observed for bound and total norisoprenoids. In Cabernet Sauvignon free, bound and total 1,1,6-trimethyl-1,2-dihydronaphtalene (TDN) was consistently increased by PF3. Hedging negatively influenced Brix and anthocyanins accumulation in 2017, and increased free norisoprenoids while decreasing the bound and total fraction. Results revealed that a high level of stress possiblt caused by excess sunlight and/or reduced photosynthesis might negatively affect norisoprenoids glycosylation. / Master of Science in Life Science / This project evaluates the effect of a grapevine canopy management practice on grape quality. The objective was to find a suitable technique to expose the fruits to sunlight in order to increase grape aroma concentration and improve grape sanitary status of Virginia vineyards. Leaves were removed from the fruit zone with different intensities at two grape developmental stages, in two varieties (Chardonnay and Cabernet Sauvignon). Treatments consisted of control, three leaves removed before blooming (PB) and three or six leaves removed after fruit set (PF3 and PF6 respectively) In an additional project with Cabernet Sauvignon, the effect of canopy height was integrated with the fruit zone defoliation. Results showed that the removal of leaves from the fruit zone is effective in improving grape sanitary status at harvest, with the improvement extent depending on the season climatic conditions and on the amount of leaves removed. Crop yield was not negatively affected by treatments. Non defoliated grapes tended to have greater acidity at harvest, while sugar responses were inconsistent. Aroma compounds responded heterogeneously to fruit zone defoliation, but volatile odorants were consistently greatest in the most exposed grapes (PF6) compared to all other treatments at harvest. Pre-bloom defoliation instead, never increased volatile aroma compounds compared to control at harvest. Generally, non-volatile odorants were greater in less severely defoliated vines or control. An overall positive effect was observed with PF3. Canopy height was demonstrated to be able to indirectly affect grape quality and composition, with the short canopy reducing grape’s sugar and color content and increasing grape’s volatile aroma compounds concentration at harvest in 2017. The removal of three or six leaves from the fruit zone in post fruit set could be a suitable practice to improve grape quality in the Virginia environment.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/87535 |
| Date | 07 February 2019 |
| Creators | Liggieri, Silvia |
| Contributors | Horticulture, Wolf, Anthony K., Stewart, Amanda C., Hickey, Cain C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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