(231) Correlation of Cluster Number and Tendril Density in Grapevines
The grapevine shoot has a zone in which leaf-opposed clusters are found at the nodes. Beyond the cluster zone, leaf-opposed tendrils are borne at the nodes in a patterned distribution. Cluster number is a primary yield component and selection programs for increasing yield in grapevine frequently consider cluster number. However, selection for increased cluster number requires direct observation, which is only possible once the vine matures. Clusters and tendrils are developmentally related, so it may be that tendril density (tendrils per node) reflects cluster number. In contrast to cluster number, tendril density can be observed on plants of all ages. The hypothesis that tendril density is related to cluster number was tested here. Cluster numbers and tendril density were assessed on 10 primary shoots each of 180 grapevine (Vitis) accessions. The accessions analyzed are cultivars and wild species collections held in the United States National Plant Germplasm System. The correlation coefficient of the number of clusters and tendril density was calculated using the means of 10 observations per accession. Tendril density was determined by calculating the mean number of tendrils per node in the nodes beyond the cluster zone. Cluster number and tendril density were positively correlated; the correlation coefficient was 0.35. This implies that vines with more tendrils per node also tend to have more clusters. The positive correlation of cluster number and tendril density has implications for grapevine improvement, pointing to the possibility of indirect selection for higher cluster number through selection for higher tendril density. Correlation between juvenile tendril density and mature cluster number is yet to be tested.