Pollination and Fruit Set: Critical Factors for the Production of the Grapevine Cultivar ‘Malbo Gentile’

‘Malbo gentile’ is a grapevine cultivar used to produce red wines in Northern Italy, whose yield is sometimes low and irregular. Morphologically hermaphrodite, functionally female flowers are reported in the ampelographic description, but their influence on yield has not been deeply examined. This study was aimed at understanding if insufficient fertilisation may explain the low yield of ‘Malbo gentile’ and how pollenizers can affect the productive performance. The trial was carried out in a ‘Malbo gentile’ vineyard far from the potential pollenizer ‘Marzemino’. Flower and pollen morphology were studied. Floral biology, fruit set, cluster and berry size, and fruit quality were analyzed comparing self-, open- and cross-pollination with six different pollen sources. ‘Malbo gentile’ flowers, featuring reflexed stamens, produced pollen that did not allow any fruit set in self-pollinated clusters. Manual cross-pollination gave always better quantitative results than free pollination; ‘Ancellotta’ was the most effective pollenizer. The effect of the distance from ‘Marzemino’ on productive performance of ‘Malbo gentile’ grapevines under free pollination was also examined. Yield linearly decreased at increasing pollenizer distance and reached a threshold of 10 m beyond which yield was too low to compensate for vineyard management costs. Cluster weight and berry number decreased, but soluble solids (Brix) increased with the distance from the pollenizer.