Fig 1.
Map of the Piedmont region (North-Western Italy) showing the presence of emerging fungus Erysiphe corylacearum, the causal agent of powdery mildew, recently introduced in Italy.
The site of samples collection indicated by a star are those where E. corylacearum is detected during 2022 field-survey, while locations marked by a dot correspond to the fungus-free zones.
Table 1.
List of Erysiphe corylacearum isolates used for the molecular identification and of their corresponding accession numbers.
Fig 2.
Symptoms of Erysiphe corylacearum on hazelnut leaves.
(A) 0.5–1 cm circular, powdery white spots and pale to yellow leaf areas on upper leaf surface; (B) White to grayish mycelium growth on fruit bracts; (C) Progressive growth of the powdery spots and turning the leaf color to purple-bronze in late infection stage.
Fig 3.
Morphological characteristics of Erysiphe corylacearum isolates from hazelnut in this study.
(A) Conidia; (B) Chasmothecium realising the asci with ascospores; (C) Ascospores; (D) Chasmothecium and its appendages. Scale bar = 20 μm (A-C), 50 μm (D).
Fig 4.
Phylogenetic analysis of Erysiphe corylacearum isolates from hazelnut obtained on the basis of ITS inferred from Maximum Likelihood analysis.
The values at the nodes indicate bootstrap support values based on 1000 replicates. For each isolate, the isolate name, the Accession Number, the host affiliation, and the geographic origin are shown. The isolates of E. corylacearum from this study are shown in bold and their collection site is shown in parentheses; (BE) = Benevello, (SL) = Serravalle Langhe. The isolate FH00941202 of Erysiphe necator was used as outgroup.
Fig 5.
Phylogram based on ITS, rpb2, CaM, GAPDH and GS sequences of the studied Erysiphe corylacearum isolates.
The site of their collection is shown in parentheses; (BE) = Benevello, (SL) = Serravalle Langhe. The concatenated phylogenetic tree was obtained by Maximum Likelihood analysis using the Tamura-Nei plus Gamma model. The isolate FH00941202 of Erysiphe necator was used as outgroup.
Fig 6.
Pathogenicity test with Erysiphe corylacearum: (a) an inoculated and (b) a non-inoculated hazelnut plant. Powdery mildew symptoms observed 20 days post-inoculation.