Optimal cluster threshold for improving yield and berry quality attributes of Alborz table grape in the inland Pacific Northwest U.S.A.

Abstract: Cluster management in table grapes is an essential cultural practice for production of high quality table grapes and this practice has not been studied in the Intermountain northwest region in the USA. Thus, the objective of this project was to determine the optimal cluster threshold for improving yield and berry quality attributes of Alborz table grape in the inland Pacific Northwest United States during 2010 through 2012. Non-thinned control vines had 71 clusters in 2010 but had 39 and 40 during 2011 and 2012, respectively. Clusters in non-thinned control vines were longer but lighter than those in the other treatments. Berries in the non-thinned control vines were always lighter in weight and smaller in size than those in the other treatments. Berries from vines with 28 clusters tended to have more uniform red color with lower overall green color while those from non-thinned control had more green color. Vines with 20 and 28 clusters tended to have greater soluble solids concentration (SSC) but those in non-thinned control and with 36 clusters had lower SSC. Overall, the cumulative yields of non-thinned control vines were similar to those with 36 clusters during two out of three years. Considering all quality attributes, between 28 and 36 clusters per vine was the optimal number for production of yield and quality attributes.