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Using the synthetic representation of root distribution presented by Giulivo and Pitacco ( 1 996), it is obvious that by root pruning 25 cm on either side of the trunk to a depth of 60 cm, a very high percentage of roots were cut from the vine. This representation indicates that the highest density of roots was contained between 40 - 90 cm from the trunk and at a depth of 25 - 35 cm. Ferree ( 1 994) also noted that new root growth after root pruning tended to occur close to the cut site, w ith very little occurring 1 5 c m away. Jordan ( 1985) suggested that root pruning may limit the uptake of nitrogen due to the reduced root volume, and therefore may reduce the incidence of BSN in this way. In

the current study ammonium concentration was lower in juice samples from root pruned vines in keeping with this hypothesis.

Nutrient uptake occurs in different types of roots at different rates. Potassium uptake is higher in young white roots than in woody roots with the reverse being true for calcium ( Kl iewer et al. , 1 983). Root pruned plants probably have a higher ratio of young white roots to older woody roots, but the total number of root tips is probably reduced. Ferree ( 1 994) found the number of roots < 1 mm in diameter to be lower in root pruned apple trees . However, there had been some growth of these roots as less than half the number of roots were > I mm in diameter for root pruned trees compared to the control . In both the current and Ferree' s ( 1 994) study, the canopy was reduced in relation to the reduced root volume. Therefore the ratio of white roots to foliage may have either increased or may possibly have been the same as for the control vines but as the amount of reduction in vegetative growth was not noted in Ferree' s ( 1 994) study this can not be determined.

Partitioning of assimilated carbon to the root system is higher in root pruned vmes ( McArtney and Ferree, 1 999a). Therefore the reduction in shoot elongation due to root pruning may be due to the root system being a more competitive sink for the assimilated carbohydrates than the shoot system, as well as being due to a reduction in the stored carbohydrates in the root system (McArtney and Ferree, 1 999a). In both the current and McArtney and Ferree' ( l 999a) study although hoot growth still increased after bloom, the rate at which shoots on root pruned vines grew was less than that of hoot on vines that were not root pruned.

Most studies indicate that root growth doe not begin until near flowering ( Richards, 1 983; Dry and Coombe, 2004), and has its first peak at flowering and its second peak around harve t, with very little growth before or during budburst or in mid summer (van Zyl, 1 988). However, some fine root growth has been found to occur in 'Concord' grapes between bud break and bloom (Bates et aI. , 2002). As reduced light intensities reduce root growth and increase the shoot root ratio (Richards, 1 983 ), shading around the time of flowering dramatically reduces root growth (Gu et ai., 1 996). In Gu et al, ( 1 996) study they found that at anthesis there was a 20% difference i n dry weight of young roots between shaded and un-shaded vines, and two weeks later, due to little root growth in shaded vines, there wa an 80% difference in root dry weight.

In our study we found little root growth prior to flowering (data not shown) confinning previous work (Gu et aI. , 1 996) and sugge ting that treatments may have affected root growth in our vines at a imi1ar time to other tudies. As most of the shade e ffect on root growth was post-flowering in other studies (Gu et aI. , 1 996), we can assume that our treatment of shade pre-FB would have had only a minor effect on root growth. However, our treatment of shade post-FB would have had an effect on root growth with the possibility of rapid root growth only occurring once the shade cloth had been removed.

Shade post-FB generall y led to an increase in B S N incidence in the year after shade had been applied. Post-FB is an important time for not only the current season's crop, but also the fol lowing season's crop. This is due to inflorescence initiation occurring

around this time and a reduction in root growth would therefore be detrimental as the uptake of some nutrients would be l imited. This in turn would reduce the availability of nutrients needed for further shoot growth, the developing berries, and the developing inflorescence. A reduction in light intensity also directly affects the actual initiation of inflore cences for the fol lowing season (Smart and Robinson, 1 99 1 ).

As the vines in our experiment were cane pruned in the winter, many of the reserves available to the developing bunch early in the next season were dependent on the cane that was formed the season before. Therefore, an altered carbohydrate and nutrient reserve may have influenced the fol lowing season' s crop, not only during the inflorescence initiation of the current season, but also during the early stages of shoot and inflorescence growth in the following season.