During the past six months we have succeeded to reproduce the flower-to-berry monitoring procedure developed in our lab with similar outcomes. The justification of this procedure is to mitigate the extreme variability of flowering events in a cluster that is assumed to explain the berry variability. Using this procedure, we were able to distinguish “early” berries (emerging from early flowering events) from “late” berries (emerging from late flowering events). Previous observations in our group suggested that flowering time was not the major contributing factor of the ripeness variability at mid- véraison stage (50%of berries are green and 50%are colored) . This was confirmed again this year via the monitoring of several phenological parameters on “early” and “late” berries. We also confirmed that the seed weight relative to seed weight better explained the ripeness of individual berries at mid-véraison stage regardless of whether berries were categorized in the early or late berry groups. Interestingly, by monitoring berry size and berry weight, we also found that “early” and “late” berries rapidly overlapped their growing curves during the early stages of the growing season (week 3 to week 6 after bloom), which suggests a developmental mechanism to mitigate developmental variability among berries of a cluster.
On the other hand, ripeness variability at véraison was not associated with berries being “early” or “late” as both berry groups had a wide range of ripeness level at mid-véraison stage (sugar and pigment content). We also validated the effects of two viticulture practices (cluster thinned and fruit-zone leaf removal) on sugar and pigment contents regardless of whether berries were “early” or “late”. In vines with clusters thinned at 0.5/shoot, both accumulation of sugar and pigment contents were significantly higher in berries during the late stages of the ripening. For the fruit-zone leaf removed, only pigment content was significantly increased in sun-exposed clusters during weeks 12-15. The fine screening we performed to mitigate the developmental variability of berries has been successfully conducted and we are in the second phase of the project this year, which is the quantification of hormone and metabolite in control, cluster thinned, and fruit-zone leaf removed grapevines.