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New Zealand Plant Protection 60 (2007): 123-127

Susceptibility of grapes to Botrytis cinerea in relation to berry nitrogen and sugar concentration

D.C. Mundy and R.M. Beresford

ABSTRACT

The percentage of detached grape berries inoculated in the laboratory that became infected by Botrytis cinerea during ripening was correlated with increasing sugar concentration and increasing yeast assimilable nitrogen (YAN) concentration. These factors could not be separated to provide a causal relationship between YAN and % berries with disease due to the close relationship that existed between sugar concentration, YAN, vine development and time. Wounding increased the percentage of berries with disease, particularly when the berries were immature. These findings do not support the hypothesis that the inherent susceptibility of grape berries to botrytis infection increases with increasing YAN. Field observations by growers that nitrogen fertiliser increases bunch rot may be due to nitrogen causing increased canopy density, which in turn causes a microclimate more conducive to the development of botrytis bunch rot.

Keywords: grape, botrytis bunch rot, berry nitrogen, sugar accumulation, wounding.

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