Sultana fruitfulness and yield as influenced by season, rootstock and trellis type

Field-grown vines (Vitis vinifera L. cv. Sultana) were examined for their f ruitfulness and yield performance over four growing seasons. Vines were eit her grafted to Ramsey rootstock (Vitis champini) or were grown on their own roots. Four commercially applied trellising systems were investigated, nam ely, a T-trellis, a Shaw trellis with a double cordon, a Shaw trellis with a single cordon and a Shaw swing-arm trellis. Fruiting potential was assess ed shortly after budburst using the Merbein bunch count method. Bunches on vines that had been counted in springtime were again counted at harvest, an d vine yield recorded. During the four years of the experiment fruitfulness was strongly influenced by growing season. Fruitfulness per node along the cane followed a well-established trend. Bud fruitfulness was close to zero in basal nodes but increased steeply thereafter reaching a maximum between nodes 8 and 10. Fruitfulness then decreased steadily. Grafted vines were a lways less fruitful than own-rooted vines, and this difference was amplifie d for all trellis designs in years when fruitfulness was low. At the time o f pruning, more canes were retained on grafted than own-rooted vines in acc ordance with the greater vigour of grafted vines. This pruning strategy res ulted in a larger number of bunches on grafted relative to ungrafted vines.