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. 2023 Jun 28;11(7):1679.
doi: 10.3390/microorganisms11071679.

First Report of Olive Branch Dieback in Croatia Caused by Cytospora pruinosa Défago

Elena Petrović  1 , Karolina Vrandečić  2 , Dario Ivić  3 , Jasenka Ćosić  2 , Sara Godena  1
Affiliations

First Report of Olive Branch Dieback in Croatia Caused by Cytospora pruinosa Défago

Elena Petrović et al. Microorganisms. .

Abstract

Olive (Olea europaea L.) is a very important crop grown in the Mediterranean part of Croatia. Olive branch and fruit dieback symptoms were observed in two olive orchards in Istria, Croatia. The samples from symptomatic trees were collected and brought to the laboratory for analysis. Based on their morphological characterization, isolated fungi were identified as Cytospora sp. Two representative isolates (one per orchard) were taken for molecular analysis, and based on DNA sequence data of the ITS and TUB gene regions, and phylogenetic analysis of the sequences, the isolates were identified as Cytospora pruinosa Défago. To determine pathogenicity, pathogenicity tests were conducted on detached olive branches and two-year-old olive trees in the greenhouse. This is the first report of C. pruinosa causing olive branch and fruit dieback in Croatia.

Keywords: Cytospora sp.; Olea europaea L.; canker; fungal disease.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Disease symptoms on olive tree in orchard. (b) Branch segment with bark discoloration taken for analysis.
Figure 2
Figure 2
(a) Cytospora pruinosa colony on PDA after 5 days in the dark at 25 °C. (b) C. pruinosa colony on PDA after 2 weeks. (c) Hyphae and spores of C. pruinosa isolate under the microscope. Scale bar = 10 µm. (d) Conidiomata formed on PDA.
Figure 3
Figure 3
The evolutionary history was inferred using the Neighbor-Joining method [42]. The optimal tree is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) is shown next to the branches [43]. The evolutionary distances were computed using the Maximum Composite Likelihood method [44] and are in the units of the number of base substitutions per site. This analysis involved 30 nucleotide sequences. Dothiorella iberica isolate 211 KP012591 was used as an outgroup. Sequences from this research are marked with red rectangles. All ambiguous positions were removed for each sequence pair (pairwise deletion option). There were a total of 769 positions in the final dataset. Evolutionary analyses were conducted in MEGA11 [45].
Figure 4
Figure 4
Disease symptoms on olive trees used in pathogenicity tests in the greenhouse after 6 months at 25 °C: (a) fruit collapse, (b) branch necrosis, (c) branch dieback, (d) bark discoloration. (e,f) Disease symptoms on olive branches used in pathogenicity tests in the laboratory: (g) Difference between the control branch inoculated with pure PDA plug (left) and the branch inoculated with C. pruinosa (right).
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