Development of thermography methodology for early diagnosis of fungal infection in table grapes: The case of Aspergillus carbonarius

Abstract

Traditional diagnostic methods employed in food mycology are based on macroscopic and microscopic characteristics and culture in appropriate media. The macroscopic methods exhibit limitations in detecting fungal development before the fruiting structures become evident. One of the imaging techniques, which have attracted attention, is infrared thermography which has been used in non-destructive monitoring of physiological status of plants. The filamentous fungus Aspergillus carbonarius is the causal pathogen of sour rot of grapes and produces ochratoxin-A, the most important mycotoxin in grapes. Ochratoxin-A has been shown to be nephrotoxic, hepatotoxic, teratogenic and immunosuppressive properties with a tremendous impact on human health. In order to assess the spatial temperature heterogeneity in A. carbonarius infected table grapes, the average temperature of the berries surface as well as the maximum temperature difference between the infected and non-infected areas of berries’ surface were calculated. The average grape temperature during the development of the fungal mycelium in the berry was significantly lower than that of the healthy one, while the maximum temperature difference increased during the fungal colonization compared to the healthy grapes that stayed constant. The estimated shape factors derived by fitting the temperature data of the thermal images to the Weibull distribution was able to identify healthy from infected berry areas even during the very early stages of A. carbonarius infection.