Contribution of grape-associated fungal species to the FMA defect on grapes and in musts

Among reported wine defects, the fresh mushroom aroma (FMA) off-odor has been linked to fungal volatile compounds (VOCs). However, the fungi causing this defect and the VOCs produced have not been fully elucidated, except for some reported FMA markers. Also, the biotic and abiotic factors impacting fungal growth and FMA production are poorly understood. Here, using a multidisciplinary approach combining predictive and classical mycology, sensorial and biochemical analyses, we determined growth patterns and VOCs profiles for 18 grape-associated fungal isolates, individually or in co-inoculation, on Meunier grapes or must media. FMA was primarily linked to Penicillium species, especially Penicillium crocicola with high intensity. On grapes, Botrytis cinerea co-inoculations with Penicillium bialowiezense or Penicllium citreonigrum led to detectable FMA off-odors and an increase in 3-octanol and 3-octanone FMA markers. Penicillium species competitively grew with Botrytis on grapes in comparison to other fungi, often leading to higher FMA perception. Fungal growth kinetics on must-based media were determined, and fastest growth rates were observed for Botrytis cinerea and Penicillium crocicola isolates although most fungi were able to grow in a wide range of conditions. Overall, our results pinpointed which individual and co-inoculated grape-associated fungi thrived on berries and in must conditions, and which combinations favored FMA off-odor production. This data can be used for better vineyard management practices and to anticipate potential conditions leading to FMA emergence in the future and in link with climate change and develop predictive tools for better vineyard management. • eighteen grape-associated fungal isolates produced detectable off-odors including fresh mushroom aroma (FMA) • fastest growth rates were observed among B. cinerea and P. crocicola isolates • fungal species thrived in conditions mimicking grape berries and must and their growth may be favored with current climate changes • fungal volatilomes determined after growth on must-based media and Meunier grapes and clusters were linked to sensorial off-odors • FMA largely associated with Penicillium species, especially Penicillium crocicola • co-inoculations between B. cinerea with P. bialowiezense or P. citreonigrum led to increased FMA related compounds and FMA off-odors