Winter buds of `Concord' and `Niagara' grapevines were dissected and their embryonic clusters scored to developmental stage. Stage was regressed against flower and fruit number per cluster the following year to see if flowering or fruiting potential could be gauged from bud morphology. `Concord' vines were either minimal-pruned (MP) or balance-pruned (BP) and non-irrigated or provided supplemental irrigation. `Niagara' vines were BP vines which were non-irrigated, irrigated, or nitrogen fertigated. Winter buds of MP `Concord' were significantly less developed than buds of BP vines, and flower and fruit number per cluster also significantly less. Irrigation did not affect bud construction or flower or fruit number per cluster in either pruning regime. Winter buds of `Niagara' had similar cluster stages in all treatments and there were similar flower and fruit number per cluster the following season. Within cultivar and year, there was a positive linear relationship between mean flower number or fruit number per cluster and mean stage of cluster differentiation within buds the previous dormant period. In `Concord', a given winter cluster stage allowed production of significantly more flowers and fruit in 1992 than it did in 1993. A bud's flowering potential thus varies from year to year and depends on factors not solely related to bud morphology.
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