Changes in Sugar, Anthocyanin, and ABA Accumulation in Response to Cluster Thinning and Girdling in Jumeigui Grape

Background and goals To overcome unsatisfactory appearance and flavor in grape berries, both cluster thinning and girdling are the practices widely applied in southern China. However, the changes in sugar, anthocyanin, and abscisic acid (ABA) accumulation under cluster thinning and girdling, as well as the interactive effects of these two practices, are poorly understood.

Methods and key findings Four treatments (control, girdling, cluster thinning, and cluster thinning + girdling) were conducted prior to veraison in Jumeigui table grapes across two consecutive seasons. It was shown that cluster thinning significantly increased sugar and anthocyanin concentrations, whereas girdling had no positive impact on these parameters at maturity. Both cluster thinning and girdling upregulated the transcript abundance of several corresponding genes involved in sugar accumulation and anthocyanin biosynthesis. The low leaf area/yield proportion under girdling against that under cluster thinning might result in low sugar and anthocyanin contents even though the transcript abundance of corresponding genes was upregulated. Furthermore, cluster thinning accelerated berry ABA biosynthesis, which was strongly correlated with the transcript abundance of NCED1 and NCED2, but girdling did not.

Conclusions and significance The acceleration of ABA biosynthesis in Jumeigui berries under cluster thinning might stimulate early sugar accumulation and anthocyanin biosynthesis, and then lead to higher sugar and anthocyanin contents than that seen with girdling. These findings will contribute to further understanding the underlying mechanism of source/sink ratio regulation, as well as to the better application of cluster thinning and girdling for grape production.