The impact of fungicide treatments on yeast biota of Verdicchio and Montepulciano grape varieties

Abstract

Yeast species that colonize the surface of grape berries at harvest time play an important role during the winemaking process. In this study, the use of culturable microbial techniques permitted a quantitative and qualitative inventory of the different yeast species present on the grape berry surfaces of Montepulciano and Verdicchio varieties when treated with conventional and organic fungicides. The results show that the most widespread yeast species at harvest time were Aureobasidium pullulans and Hanseniaspora uvarum, which are considered normal resident species and independent of the grape varieties and treatments applied. Specific differences when comparing the grape varieties were observed in species and were detected at a lower frequency; Pichia spp. were prevalent in Verdicchio, whereas Lachancea thermotolerans and Zygoascus meyerae were found in Montepulciano. In both vineyards, the farming treatments improved the competitiveness of A. pullulans, which was probably due to its reduced susceptibility to treatments that improved the competition toward other fungi. In contrast, the fermenting yeast H. uvarum was negatively affected by fungicide treatments and showed a reduced presence if compared with untreated grapes. Organic treatments directly impacted the occurrence of Issachenkia terricola in Montepulciano grapes and Debaryomyces hansenii and Pichia membranifaciens in Verdicchio. Conversely, a negative effect of organic treatments was found toward Metschnikowia pulcherrima and Starmerella bacillaris. Overall, the data suggest that the yeast community colonizing the grape berry surface was influenced by both grape variety and farming treatments, which characterized the yeast biota of spontaneous must fermentation.

Fig 1. Mean values (%) of the initial yeast community in Verdicchio and Montepulciano grapes.

Fig 2. The average percentages of yeast species detected in organic, conventional and non-treated samples of Verdicchio and Montepulciano grapes at harvest time.

Fig 3. Average percentages of yeast species detected in organic, conventional and non-treated samples of Verdicchio and Montepulciano samples after 7 days of fermentation.

Fig 4. Average percentages of yeast species detected in organic, conventional and non-treated samples of Verdicchio and Montepulciano samples after 15 days of fermentation.

Fig 5. Principal component analysis related to the yeast community of samples coming from Verdicchio (V) and Montepulciano (M) vineyards subjected to organic (O) and conventional (C) fungicide and non-treated (NT) treatments.

(a) The yeast community on the grape surface detected at harvest time; (b) the yeast community of samples at 7 days of spontaneous fermentation; and (c) the yeast community of the samples at 15 days of spontaneous fermentation. A. pullulans (Ap); I. terricola (It); C. californica (Cc); Z. meyerae (Zm); Cryptococcus spp. (Cry); L. termotolerans (Lt); S. bacillaris (Sb); Rhodotorula spp. (Rh); M. pulcherrima (Mp); H. uvarum (Hu); D. hansenii (Dh); Z. bailii (Zb); P. fermentans (Pf); P. sporocuriosa (Ps); P. membranifaciens (Pm); T. delbrueckii (Td); C. diversa (Cd); P. kudriavzevii (Pk); W. anomanuls (Wa); S. cerevisiae (Sc).