Detecting and quantifying grey mould contamination of grapes is problematic as Botrytis cinerea frequently colonises the interior of the grape bunch and is hidden from immediate view. This is especially the case in varieties that produce tightly packed grape clusters. Furthermore, the disease is harder to identify on red-skinned grape varieties and can sometimes be confused with other physiological or pathological disorders of the vine. Despite this, current wine industry practises largely rely on visual assessment of vineyards and grapes at harvest, a subjective method fraught with difficulty. Consequently, it is not that unusual for even experienced grape growers to confuse grey mould with other grape rotting fungi or even physiological disorders such as heat damage. Some grape growers and wine makers measure gluconic acid, activity of the fungal enzyme laccase (which is responsible for wine oxidation), and occasionally measurements of grape and / or wine colour as an overall measure of grape quality. However, none of these measures are specific for B. cinerea. A further technique which is yet to be widely adopted, involves immunodetection where monoclonal antibodies are employed to detect Botrytis antigens (Dewey et al., 2013).
In this work a commercially available Botrytis antigen detection kit, Botrytis Alert (Mologic, 2024) was compared with visual assessments of grey mould infection. Ergosterol, a sterol unique to fungal cells was also measured to obtain an estimation of the total fungal biomass present in grape samples (Porep et al., 2014).
Antigen analysis of uninfected grape homogenates supplemented with known amounts of freeze-dried B. cinerea mycelium revealed a linear relationship between B. cinerea dry mass and the signal intensity (SI) of the antigen detection device.
Grape bunches (n =268) with varying levels of grey mould infection were collected from commercially vineyards in NSW and VIC, visually assessed for grey mould, analysed using the Botrytis Alert kit and the ergosterol content determined. Although there were slight differences between different grape cultivars, in all cases a stronger correlation was found between ergosterol analysis and antigens than when either ergosterol or Botrytis antigens were compared with visual assessment.
The genus specific nature of the Botrytis Alert kit provided a definitive and rapid (10 minutes per sample) quantitative determination of the presence of grey mould in grape samples, superior to visual assessments and other assessment measures, currently used in the wine industry.