First Report of Grape Root Rot Caused by Roesleria subterranea in South Tyrol

Erstnachweis der durch Roesleria subterranea verursachten Traubenwurzelfäule in Südtirol
Prima segnalazione di marciume della vite causato da Roesleria subterranea in Alto Adige
Andreas Gallmetzer1, Christian Springeth1, Yazmid Reyes Dominguez1
1 Laimburg Research Centre, 39040 Auer/Ora, BZ, Italy
Cite article as
Gallmetzer Andreas, Springeth Christian, Reyes Dominguez Yazmid (2024). First Report of Grape Root Rot Caused by Roesleria subterranea in South Tyrol. Laimburg Journal 06/2024.005
DOI: 10.23796/LJ/2024.005
Corresponding Author
Yazmid Reyes Dominguez
Laimburg Research Centre, Laimburg 6 – Pfatten/Vadena, 39040 Auer/Ora, BZ, Italy
yazmid.reyes-dominguez@laimburg.it
+390471969587
Keywords
grape root rot, fungi, grapevine, root decay

In April 2023, declining grapevines were observed in a twenty years old vineyard (Vitis vinifera cv. Lagrein) in the province of Bolzano. Affected vines were stunted with shortened internodes and yellow leaves; others had dead cordons or were entirely dead. The grower reported that vines were losing vigour and collapsing. Several symptomatic vines showed signs of root decay. Infected plants were usually found in groups and were patchy within the vineyard.

At the level of the roots, the diagnosis was not as easy as with other root pathogens. In fact, the root was not easy to pull out from the ground, did not appear rotten and there were no signs of fungal mycelium present. This could erroneously suggest that the problem was not root rot. The only useful clue that it was a fungal infection was the presence of mazaedia (distinctive fruiting bodies) below the soil line (Fig. 1). Mazaedia are stalked apothecia with spores, produced in evanescent asci in dried masses similar to the mazaediate lichens. The mazaedia were approximately 7 mm in length with grey, hemispherical heads. Ascospores were uniseriate, lens-shaped and septate across the broadest plane, hyaline or light green (Fig. 2). The fungus was cultured from ascospores on potato dextrose agar (PDA) at 22 °C for seven days. A fluffy, mycelial mass was produced with a green pigment in the centre of the colony. No spores were produced (Fig. 3).

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Fig. 1: Vine roots infected with R. subterranea. The circles indicate the presence of mazaedia.

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Fig. 2: Ascospores of R. subterranea.

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Fig. 3: In vitro growth of R. subterranea.

DNA was extracted, and the internal transcribed spacer (ITS) region was amplified by using the primers ITS5 (5'-GGAAGTAAAAGTCGTAACAAGG-3') and ITS4 (5'-TCCTCCGCTTATTGATATGC-3') [1]. Sequences obtained by PCR were blasted (NCBI Nucleotide Blast). The isolate showed 99.04% identity and an E-value of 0 to Roesleria subterranea-type culture CBS:407.51 (accession number MH856922.1).
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  • [1] White T.J., Bruns T.D., Lee S.B. et al. (1990). Amplification and Direct Sequencing of Fungal Ribosomal RNA Genes for Phylogenetics. In: Innis M.A., Gelfand D.H., Sninsky J.J. et al. (eds.). PCR Protocols. A Guide to Methods and Applications. Academic Press, New York, USA, here pp. 315-322, DOI: 10.1016/B978-0-12-372180-8.50042-1
Until recently, R. subterranea was regarded as an opportunistic secondary invader of damaged roots or weakened hosts. It is often found in deciduous trees of genera such as Malus, Pyrus, Prunus, Salix, Cydonia and Rosa. It was assumed to be a facultative parasite of grapevine (Vitis vinifera) and prior to the development of molecular diagnosis techniques the fungus was long confused with the morphologically very similar lichen Sclerophora pallida [2].
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  • [2] Degawa Y., Hosoya T., Hosaka K. et al. (2015). Rediscovery of Roesleria subterranea from Japan with a discussion of its infraspecific relationships detected using molecular analysis. MycoKeys (9), 1-9, DOI: 10.3897/mycokeys.9.6564.
A study conducted in the German winegrowing regions where this ascomycete caused serious problems in established vineyards demonstrated that R. subterranea is not a minor, but rather a primary, pathogen of grapevines and fruit trees. In this study, a pest risk analysis was carried out according to the guidelines defined by EPPO standard series PM 5/3 [3]. The results of this study show that R. subterranea must be considered to be a serious, primary pathogen for grapevines and fruit trees that can cause massive economic losses [4].
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In fact, it was shown that the hyphae of R. subterranea aggregate particularly in the xylem and block the water transport vessels leading to root damage and dieback [5].
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This is the first report of R. subterranea on grapes in Northern Italy. This fungus needs to be recognised as a potential cause of vine decline and replant problems.

References