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-gr own Muler-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 flowe ring. Nitrogen supply reduced symptoms of inflorescence necrosis and improv ed fruit set, but increased bunchstein necrosis, Botrytis cinerea bunch rot and yield. This was associated with reduced grape sugar, higher acidity an d 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 x rootstock inte ractions were rare and contributed little to total variance, suggesting tha t rootstock-induced differences in scion performance were, except for SO4, largely independent of soil nitrogen level.