Influence of crop load and cultivar's dependent canopy management on grape must quality of 'Sipon', 'Zametovka' and 'Rebula'

‘Sipon’, ‘Zametovka’, and ‘Rebula’ are locally spread grapevine (Vitis vinifera) cultivars in Slovenia. Appropriate must sugar and acid contents are not reached with these cultivars, because of their genetically dependent great fruitfulness and unsuitable canopy management practices. To improve their must quality, experiments were done for three years (1995-1997) in which vineyards of ‘Sipon’, ‘Zametovka’, and ‘Rebula’ were involved. Training system performed for each cultivar was double Guyot. All three experiments were grounded as block trial with two factors: crop load (two levels) and canopy management (three levels). At the harvest, yield per vine and must sugar and acid contents were recorded. Individual vine data were analysed with Analysis of variance, averaged by the treatment means in each year and compared with the Duncan test at p=0.05. Lower number of buds per vine of ‘Sipon’ and ‘Zametovka’ significantly lowered the yield per vine in all three years and only in 1996 for ‘Rebula’. Cluster thinning or cluster shortening had no significant effect on the yield per vine of ‘Sipon’ and ‘Zametovka’, but cluster thinning of ‘Rebula’ significantly decreased it in 1995 and 1997. Higher must sugar content of ‘Sipon’ and ‘Zametovka’ was reached by the lower yield charge (20 buds per vine). The latter had no significant influence on the must sugar content of ‘Rebula’. Commonly used canopy management practices, consisting of shoot positioning, suckering, lateral removal, and topping significantly increased must sugar content of ‘Sipon' and ‘Zametovka’. Additional cluster thinning and leaf removal of ‘Sipon’ grapevines had no significant effect on the must quality. However, additional cluster shortening of ‘Zametovka’ significantly increased the must sugar content in two out of three years. Better must quality of ‘Rebula’ was attained by cluster thinning but only in 1997. The total acid content was the least changeable parameter in our trials.