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P.A. Bowed and W.M. Kliewer

Yield components responsible for yield variation within and among three `Cabernet Sauvignon' grape (Vitis vinifera L.) clones in a cane-pruned vineyard were determined over 2 years using a multivariate analysis procedure, two-dimensional partitioning (TDP). TDP analysis indicated that canes were producing at their capacity and yield per vine was limited by the number of canes retained. Yield per cane was limited by the portion of nodes at which shoots developed, and yield per shoot was limited by cluster number and fruit-set. The highest-yielding clone bore more fruit on non-cane shoots and fewer and larger clusters on cane shoots than the moderate-yielding clone. Poor fruit-set exhibited by the lowest-yielding clone resulted from inadequate or inviable pollen. In one year, thicker canes were more productive than thinner canes due to better bud burst and fruit set.

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P.A. Bowen and W.M. Kliewer

Two-dimensional partitioning of variation was used to determine the sources of relationships between the yield and vegetative characteristics of three `Cabernet Sauvignon' grape (Vitis vinifera L.) clones. Clonal differences were found in shoot growth rate, but not in duration or total growth. A weak positive relationship between total shoot growth and yield resulted from a positive relationship between fruit set and growth duration. Relationships between cluster number and foliar characteristics indicated that light exposure in the previous year may have influenced both vegetative and reproductive development. The mean number of clusters per bud was positively related to the mean area, dry weight, and nitrogen content of leaves.

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N.K. Dokoozlian and W.M. Kliewer

Potted `Cabernet Sauvignon' and `Pinot noir' grapevines (Vitis vinifera L.) grown in a sunlit phytotron were used to study the influence of cluster light exposure during various stages of fruit development on berry growth and composition. Clusters grown without light during berry development stages I and II, stage III, or stages I, II, and III, were compared to clusters exposed to light throughout fruit development (control). The temperature of light-exposed and nonexposed fruit was similar. The weights and diameters of berries grown without light during stages I and II, or stages I, II, and III, were similar and significantly lower than those of the control. Fruit softening in both cultivars, as well as the initiation of berry coloration, was delayed when berries were grown without light during stages I and II. Following fruit softening, berries grown without light during stages I, II, and III were lower in sugar than the control. On the final sample date, `Cabernet Sauvignon' berries grown without light during stages I, II, and III were higher in malate compared to the control. `Pinot noir' berries grown without light during stages I and II, or stages I, II, and III, were lower in malate before fruit softening, and higher in malate following fruit softening, than the control. Control berries had greater skin anthocyanins and phenolics compared to the remaining treatments. Berries grown without light during stages I and II, or stage III, were greater in anthocyanins and phenolics than fruit grown without light during stages I, II, and III. Light had no effect on fruit tartrate concentration or juice pH. Light had its greatest impact on fruit development during the initial stages of berry growth. Berry growth was reduced and ripening delayed when fruit were grown without light during stages I and II. Normal fruit development was not fully restored when these fruit were exposed to light during stage III.