Influence of Woody Lateral Shoot Presence on 'Pinot noir' Bud Fruitfulness

Grapevine bud fruitfulness, the number of inflorescence primordia within the dormant compound bud, has been linked to carbon assimilation and/or carbohydrate reserves in several studies. Summer lateral shoots, which arise from the same leaf axil as the compound bud, require assimilates early in their formation, potentially competing with inflorescence primordia in the newly developing bud. Laterals can become lignified by dormancy, and the presence of a woody lateral at a given node was investigated for its impact on bud fruitfulness (FFL) and on the Integrated Fruitfulness Index (IFI) which is the sum of inflorescence primordia diameters in the bud. A total of 240 one-year canes were collected from fruiting arms (2-year old canes) and 120 canes from renewal spurs of ‘Pinot noir’ at dormancy in early 2015. Canes were weighed and dormant compound buds from nodes five to 15 (as laterals are uncommon at nodes one to four) were evaluated for FFL and IFI within each of the three buds within the compound bud, and the presence of a woody lateral was noted for each. Node position, cane weight, and lateral presence influenced both FFL and IFI determined by multiple regression, with significant interactions for cane weight x lateral presence and node position x lateral presence. Data were then paired by presence or absence of lateral for each node and field plot and paired t-tests were run. Given the same node position, buds at nodes with a lateral present had 25% to 83% higher FFL and 29% to 100% higher IFI than those without laterals. The increase in FFL and IFI was due to higher primary bud FFL and IFI at all nodes except node five and higher FFL and IFI in secondary buds at all nodes except nodes seven and ten. At a given node position, a heavier cane had a higher FFL and IFI than the same node on a lighter cane, given the presence (or absence) of a woody lateral at both nodes. These findings suggest that nodes with woody laterals at dormancy do not limit inflorescence primordia initiation or growth compared to nodes without a lateral at dormancy, possibly through increased photoassimilation of the subtending lateral. To the authors’ knowledge, this is the first association in wine grapes for increased fruitfulness at nodes with woody laterals present.