Josh Vander Weide and Simone Castellarin*
*University of British Columbia, 2329 West Mall, Vancouver, British Columbia, V6T 1Z4, Canada (simone.castellarin@ubc.ca)

Volatile compounds, particularly terpenes and C13 norisoprenoids, are highly subject to modulation during berry ripening. Solar radiation also affects production of grape volatiles. Despite this knowledge, little is understood regarding the specific sensitivity of both free and bound volatiles to berry maturity and solar radiation. To investigate this, a 2 × 2 factorial experiment was established using greenhouse-potted (Vitis vinifera L.) Riesling vines. The first treatment involved altering berry maturation at 50% veraison (~8 Brix) by girdling shoots above and below clusters to estimate the effect of halting berry maturity on volatile production. Second, clusters were covered with light-impenetrable bags at the same point, halting light exposure on volatile production. “Girdling” and “bagging” treatments were compared to vines subjected to a combination of both treatments and an untreated control. In addition to gas exchange and basic fruit quality parameters, free and glycosylated volatiles were profiled from lag phase to harvest maturity stages, including at two (~9 Brix), 10 (~14 Brix), and 30 days (~21 Brix) post-treatment to gauge short-, mid-, and long-term responses to treatments. Solar radiation was reduced to <2 µmol m2/s, while berry temperature was not altered by either treatment. Photosynthesis was significantly decreased by girdling from one week post-treatment until harvest due to feedback inhibition. Total soluble solids were unaffected by bagging but were significantly decreased by girdling. An immediate decrease in the concentration of select volatiles was observed at two days post-bagging; however, this effect was delayed in response to girdling. Volatiles influencing Riesling varietal character were affected by both treatments. Bagging had a faster and more severe impact on the reduction of free and bound volatiles in Riesling than limitation of berry maturity due to girdling, highlighting the importance of solar radiation in volatile development during berry ripening.

Funding Support: NSERC Discovery