Two common, yet expensive, practices used in viticulture are cluster thinning and cluster-zone leaf removal, which are intended to alter environmental conditions in hopes of causing the vine to respond in a favorable manner (e.g., improved fruit quality or disease management). Because the vine’s response to environmental changes is principally hormone-mediated, we profiled the active forms, conjugates, and precursors of auxin, cytokinin, gibberellin, abscisic acid, brassinosteroid, jasmonic acid, and salicylic acid to understand the physiological effects of cluster thinning and leaf removal on the dynamic accumulation of these compounds in the berry. Similarly-developing berries were identified during the growing season and their tissues separated (seed, pulp, and skin). For the cluster-thinned treatment, clusters were thinned to 0.5 clusters/shoot; 100% of the cluster-zone leaves were removed for the leaf-removal treatment. Phytohormones were extracted using a targeted method developed within our laboratory. Preliminary findings from the first year’s data are consistent with literature, but revealed a clear tissue- and stage-specific distribution of the bioactive forms of hormones. We also observed new accumulation patterns for gibberellic acids and brassinosteroids during preripening stages in skin and pulp, suggesting a role in ripening initiation. The treatment effects were largely negligible for many hormones. However, treatment effects reduced hormone concentrations in several cases. Leaf-removal treatment effects included a preveraison decline in abscisic acid, and both treatments reduced concentrations of indole-3-acetic acid (auxin), trans-zeatin (cytokinin), and castasterone (brassinosteroid) in both pericarp tissues. Though both treatments reduced hormone concentrations, leaf-removal treatment effects were more significant than those of cluster-thinning. The implications of these early findings are yet opaque but are likely to be clarified with a second year of data.

Funding Support: Oregon Wine Board