The influence of nitrogen supply and deficit irrigation on growth and quality parameters in wine grapes : susceptibility in Botrytis cinerea Pers. : Fr.infection.

Vine nutrition, particularly N application in wine grapes, is well known to enhance vine vigour and consequently grape and wine quality. Less is known about the interactive effects of N and irrigation on wine quality and Botrytis bunch rot incidence and severity. The Australian Wine Industry in its 5-year research plan (2002-07) identified Botrytis management strategies as a key area requiring a novel approach for minimizing fungicide application, which is critical to marketing of Australian wine both for the domestic and export markets. This study investigated the role of N nutrition and irrigation management for improving vine vigour, quality and yield of fruit through changes in canopy density and improving cuticular thickness of berries for Botrytis cinerea control using Chardonnay in two field-based (vineyard) trials and Chardonnay and Cabernet Sauvignon in glasshouse-based trials. In the first and second year vineyard trials, 0,30 and 300 kg ha-1N were applied to the soil either with or without irrigation. Effects of N nutrition on B. cinerea infection were also investigated using varieties Chardonnay and Cabernet Sauvignon in glasshouse trials under controlled conditions. Nitrogen (N) application in the glasshouse trials ranged from 25-400 kg ha-1. A leaf bioassay was developed to investigate the infection on leaves across varying N levels. Additional studies looked at effects of N treatment on the severity of B. cinerea infection in berries and resveratrol (stilbenes) in grape leaves, berries and wine in vineyards. In both vineyards, the N applied did not result in significant changes in canopy density, shoot length, yield, or wine quality parameters (OBrix, pH, acidity, total phenols, and N in berries). Also, no significant differences were seen in different levels of N treatment with respect to B. cinerea severity, and stilbene levels in vines over a 2-year period. In glasshouse trials, low N levels (25 kg ha-1) resulted in reduced shoot vigour, low yields and high susceptibility to infection. In contrast, N applications (200 and 400 kg ha-1) maximized vigour (wet cane weight) and imparted resistance in Chardonnay against B. cinerea infection. In Cabernet Sauvignon, the highest level of N application (400 kg ha-1) proved most beneficial in improving vigour and resistance against B. cinerea infection. Preliminary (qualitative) studies on the wax morphology of the berry surface using scanning electron microscopy (SEM) revealed delayed secondary wax plate formation during the veraison period in some replicates of the high N and no irrigation treatment. Further intensive studies would be needed to explore this observation. Light microscopy studies performed to assess the cuticular thickness of the berry at different N treatments did not show any appreciable changes at different stages of berry growth. Field experimental results have implications for farmers and suggest that in regions where vines and soil are not deficient in N, grape growers could avoid excessive soil application of N fertilisers and irrigation to enhance vine vigour for minimizing B. cinerea infection.