Background and Aims: Inflorescence morphology, flower formation and subsequent fruit development of grapevines are influenced by genetic, environmental and cultural practices. While the effect of temperature on inflorescence primordia number per bud is documented, its effect during dormancy and budburst (BB) on floral development is less clear. In our study, winter dormant buds were passively heated for different periods of time from mid‐winter (July) to BB (October). Methods and Results: Individual canes were heated pre‐BB for different periods in polyethylene tunnels. Heating during winter dormancy had no effect on the number or position of inflorescences on the shoot, or on the type of structure occurring at the outer arm position of the inflorescence. Heating buds for either July or August to BB advanced the date of BB and the start date of flowering by 12–14 and 14 days, respectively, compared with that of the unheated Control treatment. There was a significant (P < 0.05) negative correlation between the mean temperature 12 days pre‐BB and flower number per shoot. The time between 50% flowering and the fruit TSS reaching 14°Brix was not influenced by winter heating or the date of flowering; the difference in this time interval, however, between the inner and outer arm components increased as shoot node number increased. Conclusions: Flower number per inflorescence had the greatest influence on the proportion of fruitset. The date of flowering of the outer arm was later at higher inflorescence positions on the shoot and later than that of the inner arm. Likewise, the outer arms of bunches higher up the shoot took longer from flowering to accumulate a fruit TSS of 14°Brix. Significance of the Study: Much of the within‐vine variability in berry composition at harvest can be attributed to the position of bunches on the shoot and the presence of an outer arm. The outer arm on apical bunches took significantly longer to progress from flowering to a fruit TSS of 14°Brix, suggesting that removal would significantly reduce within‐vine fruit variability.
Background and Aims: Inflorescence numbers per shoot and their size vary between seasons and may, within a season, be affected by pruning systems, bud position along a cane and the size of the cane. A grapevine inflorescence typically has a main rachis and a tendril, which may or may not have flowers (an outer arm). The aim of this study was to identify the effect of these factors during inflorescence primordia (IP) initiation on the resulting number of inflorescences per shoot and their architecture. Methods and Results: Two-cane, four-cane and spur-pruned Sauvignon Blanc vines were used to investigate changes in inflorescence number, distribution and architecture over two growing seasons. The pruning system had no effect on the inflorescence number per shoot (fruitfulness), inflorescence architecture or distribution at a given cane node number. There were differences in inflorescence number and structure between the seasons, likely associated with air temperatures during primordia initiation. A warmer initiation period was associated with an increase in the occurrence of flowers on the outer arm and lower positions of the basal inflorescences (shoot bud position). An increase in cane cross-sectional area correlated to an increase in fruitfulness and an increase in the average occurrence of an outer arm with flowers along a cane. Conclusions: Inflorescence number, the position of the basal inflorescence on the developing shoot and the development of the outer arm are affected by the bud position of the shoot along a cane, the cross-sectional area of the cane and the season. Our results suggest that initiation of IP may occur at the same time for all bud positions along a shoot, so long as they are free from inhibiting factors. Significance of the Study: Cane selection can be used to modify inflorescence number and architecture and thus the potential yield of grapevines.
The influence of restricting available carbohydrates (CHOs) on shoot growth was studied by cane girdling field grown Vitis vinifera L. Sauvignon Blanc grapevines before budbreak. Canes were girdled 5, 10 or 20 cm from the terminal bud of the cane, and the shoot growth of the terminal bud was monitored over the course of a single growing season. A linear relationship was found between the initial rate of shoot growth and the amount of cane isolated by the girdle. A decrease in available CHOs during initial shoot growth appeared to inhibit the shoot’s ability to produce new vegetative nodes past the point of discontinuity, resulting in a decrease in total leaf area due to incomplete leaf expansion. The transition from the vine’s dependence on reserve CHOs to a net positive state appeared to occur when shoot growth reached a steady state. In the case of severe CHO restriction, no lateral growth occurred, suggesting the CHO status in the vine may play a role in lateral bud growth. The cross-sectional area of canes or shoots were shown to have a linear relationship to their CHO content, which allows for an estimation of the amount of CHOs required to obtain growth similar to the control treatment. Additionally, main shoot leaf area can be used to predict total CHO content in the shoot at harvest.
Background and Aims Inflorescence primordia (IP) development starts in the buds of leaf axils approximately 12 months before flowering. Primordia initiation progresses acropetally as the shoot develops, although little is known about the timing of initiation at different node positions up the developing shoot. Girdling and/or leaf removal treatments were used to investigate the timing of development and structure of grapevine inflorescences at different positions along the shoot. Methods and Results Individual shoots were either girdled at their base shortly after fruitset or left intact. Leaves were then removed from those shoots on four occasions from the time of girdling to natural leaf fall in the autumn. Dormant latent buds from treatment shoots (shoot node positions one to ten) were grown as single‐node cuttings (SNCs) in a glasshouse, and the inflorescence number per SNC and their architecture were scored on developing shoots. Girdling fully leafed shoots increased the proportion of SNC basal inflorescences with an outer arm but had no effect on the number of inflorescences per SNC. Girdled shoots that had their leaves removed at 0 or 4 weeks post‐fruitset had a decrease in inflorescence number per SNC and outer arm development from nodes six and eight, respectively. Conclusions Inflorescence initiation before node positions six and eight was complete by the time girdling and leaf removal treatments were applied, and initiation at nodes six and eight occurred at 0 and 4 weeks post‐fruitset. The development of the apical IP and the outer arm of the basal IP appears to occur at the same time. Significance of the Study This study presents novel information regarding the timing of IP initiation at different positions along the developing shoot, including the initiation and development of the outer arm. Also, the formation of an outer arm is shown to be sensitive to girdling and/or leaf removal.
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