Assessment of bud fruitfulness of three grapevine varieties grown in northwest Portugal

Assessing bud fruitfulness (fertility) before budburst can provide useful information for determining the yield potential for the following growing season and allows the number of buds per vine to be adjusted according to the productive potential of each season. The present study aims to assess bud fruitfulness and the incidence of necrotic buds using different analysis techniques in three spur pruned (cordon) grapevine white varieties planted in the Vinhos Verdes Demarcated Region (VVDR), NW Portugal. The first two dormant buds and cane samples were collected before winter pruning in December 2016 and 2017 from three (Vitis vinifera L.) varieties (Alvarinho, Fernão-Pires and Loureiro) in two different VVDR sub-regions. The fruitfulness and the incidence of bud necrosis were determined using anatomical bud analysis and by forcing bud growth under controlled environmental conditions. Additional analyses were performed to determine the total soluble sugars and starch in cane samples on node and internode regions. There were significant differences in fruitfulness among varieties over the two growing seasons (2016/2017 and 2017/2018). The Fernão-Pires variety showed the highest bud fruitfulness for the two first buds of the three varieties. Total soluble sugars and starch content were influenced by the site, variety and position on the cane. A year-to-year variation was observed, with a decrease in bud necrosis and an increase in the fruitfulness indices and carbohydrates content from 2016/2017 to 2017/2018. To our knowledge, no previous studies combining anatomical and forced bud growth techniques have been carried out on these three white varieties.