Dynamics of grape berry volume change during ripening

Marco Biondi

Vitis vinifera L. (c.v. Merlot) and Vitis labruscana Bailey (c.v. Concord) were used in this study to better understand the dynamics of fruit volume change during grape ripening. Berry diameter was monitored during dry-down and re-watering cycles at veraison. The diameter of green berries declined during dry-down and increased when the skin changed color even though water was not available in the soil. The increase in berry size which was accentuated by re-watering may be due the increase of phloem influx. Leaf photosynthesis also increased within two hours of rewatering. Pressurizing the root system of Concord vines during veraison showed that berries respond to pressure by increasing their volume up to a soluble solids concentration of 9 Brix and sometimes cracked at >11 Brix. When the xylem-mobile dye, basic fuchsin, was infused through the shoot base, the dye penetrated through the berry's vascular system. Dye penetration decreased as the berry skin changed color from green to blue. This trend could be reversed by pressurizing the shoot base. When dye was infused through the stylar end of post-veraison berries, it moved back to the plant only when pressure applied to the root was released. This proves that the xylem vessels are perfectly functional and the berry is not hydraulically isolated from the rest of the plant during ripening. Berries immersed in distilled and tap water absorbed water through the skin and pedicel regardless of the variety, water source and maturity stage. Post-veraison berries were likely to crack and when they did, they lost up to 300 mg of sugar. Cracked berries gained more weight in distilled water than in tap water which might be explained by the difference of mineral concentration in the water source. Even if the berries did not crack, sugar leached out of the berry from the pedicel. When clusters were girdled or detached shortly before veraison, berries changed color similar to intact clusters. However, this was only true when the berries shriveled. Berry color change may be trigged by the sugar concentration which increases due to water loss or phloem influx.

Dynamics of grape berry volume change during ripening

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