Reproductive growth of grapevines in response to nitrogen supply and rootstock

Nitrogen fertiliser was applied at two rates (0 or 100 kg N/ha) to field-grown Müller-Thurgau grapevines grafted onto six rootstocks (Kober 5BB, Teleki 5C, Teleki 8B, Selection Oppenheim 4, Couderc 3309, Ruggeri 140). Half the nitrogen was applied four weeks pre-flowering and half at the end of flowering. Nitrogen supply reduced symptoms of inflorescence necrosis and improved fruit set, but increased bunch-stem necrosis, Botrytis cinerea bunch rot and yield. This was associated with reduced grape sugar, higher acidity and lower pH. Rootstocks had no significant effect on inflorescence necrosis, bunch-stem necrosis and bunch rot, but vines grafted on C-3309 and Ru-140 had both lowest yields and highest fruit quality. Nitrogen × rootstock interactions were rare and contributed little to total variance, suggesting that rootstock-induced differences in scion performance were, except for SO4, largely independent of soil nitrogen level.