First description of adenosine production by Gnomoniopsis smithogilvyi, causal agent of chestnut brown rot.

Gnomoniopsis smithogilvyi (Gnomoniaceae, Diaporthales) is the main causal agent of chestnut brown rot on sweet chestnut worldwide. The rotting of nuts leads to alterations in the organoleptic qualities and decreased fruit production, resulting in significant economic losses. In 2021, there was an important outbreak of chestnut rot in southern Galicia (Spanish northwest). The profile of secondary metabolites from G. smithogilvyi was studied, especially to determine its capability for producing mycotoxins, as happens with other rotting fungi, due to the possible consequences on the safety of chestnut consumption. Secondary metabolites produced by isolates of G. smithogilvyi growing in potato dextrose agar (PDA) medium were identified using liquid chromatography coupled with high-resolution mass spectrometry. Three metabolites with interesting pharmacological and phyto-toxicological properties were identified based on their exact mass and fragmentation patterns, namely adenosine, oxasetin, and phytosphingosine. The capacity of G. smithogilvyi to produce adenosine in PDA cultures was assessed, finding concentrations ranging from 176 to 834 µg/kg. Similarly, the production of mycotoxins was ruled out, indicating that the consumption of chestnuts with necrotic lesions does not pose a health risk to the consumer in terms of mycotoxins.

First detection of mycoviruses in Gnomoniopsis castaneae suggests a putative horizontal gene transfer event between negative-sense and double-strand RNA viruses.

Gnomoniopsis castaneae is an ascomycetous fungus mainly known as a major pathogen of chestnut causing nut rots, although it is often found as an endophyte in chestnut tissues. To date, no virus has been reported as associated with to this fungus. Here, a collection of G. castaneae isolates from several European countries was screened to detect mycoviruses infecting the fungus: for the first time we report the identification and prevalence of mitovirus Gnomoniopsis castaneae mitovirus 1 (GcMV1) and the chrysovirus Gnomoniopsis castaneae chrysovirus 1 (GcCV1). Interestingly, we provide evidence supporting a putative horizontal gene transfer between members of the phyla Negarnaviricota and Duplornaviricota: a small putative protein of unknown function encoded on the RNA3 of GcCV1 (Chrysoviridae) has homologs in the genome of viruses of the family Mymonaviridae.

The Fungal Pathogen Gnomoniopsis castaneae Induces Damaging Cankers in Multiple Domestic Fagaceae Species.

Gnomoniopsis castaneae is internationally recognized as a destructive pathogen of chestnut species. Primarily associated with nut rot, it has also been associated with branch and stem cankers of chestnut and as an endophyte of multiple additional hardwood species. The present study evaluated implications of the recently reported United States presence of the pathogen for domestic Fagaceae species. Stem inoculation assays of Castanea dentata, C. mollissima, C. dentata × C. mollissima, and Quercus rubra (red oak) seedlings were utilized to examine the cankering ability of a regional isolate of the pathogen. The pathogen induced damaging cankers in all assessed species and significant stem girdling in all chestnut species. No previous study has associated the pathogen with damaging infection in Quercus species, and its presence in the United States has the potential to compound ongoing chestnut recovery programs and oak regeneration problems within forest systems.

First report of Gnomoniopsis smithogilvyi causing chestnut brown rot on nuts and burrs of sweet chestnut in Spain.

About 60% of the nut production of sweet chestnut (Castanea sativa Mill.) in Europe originates in Spain (FAOSTAT, 2022), mostly (91%) in Galicia (NW Spain). In September 2021, premature fall of immature chestnut burrs and nuts of C. sativa was observed in eight orchards of Pontevedra and Ourense (provinces of Galicia). Chestnut green burrs had turned brown and fallen off, and the nuts showed brown lesions in kernels and embryos. Some nuts had become mummified. Symptomatic samples of burrs and nuts, including mummified fruits, were collected. Small pieces of samples were surface-disinfected with 2% sodium hypochlorite, and plated onto potato dextrose agar (PDA) plates. Colonies were creamy white to gray or light brown, and presented a woolly to felty mycelium with a dense development in concentric circles. Brownish to black conidiomata, produced abundantly, were globose to sub-globose. Conidia were hyaline, oval, obovoid, fusoid and multi-guttulate, and 6.6±0.78 [5.07 to 9.01] µm x 3.2±0.43 [2.41 to 4.38] µm in size. These features matched those described for Gnomoniopsis smithogilvyi (Shuttleworth et al. 2012), syn. G. castaneae (Visentin et al. 2012; Shuttleworth et al. 2015). Genomic DNA was extracted from mycelium developed in 22 burrs and nuts, and 30 pure cultures. The rDNA internal transcribed spacer (ITS), fragments of the ß-tubulin (TUB2) and the translation elongation factor-1α (TEF-1α) genes were amplified using ITS1F (Gardes and Bruns 1993) and ITS4 (White et al. 1990), T1/Bt2b (O'Donnell and Cigelnik 1997), and EF1-728F/EF1-986R (Carbone and Kohn 1999) primers, respectively. Two isolates (EFA 924A, EFA962.4A) were deposited in the Spanish Type Culture Collection (Paterna, Valencia), and their sequences submitted to GenBank (accession nos.: ITS: OM319846, OM319848; TUB2: OM417078, OM417080; TEF-1α: OM417081, OM417083). BLASTn analyses showed: for ITS and TEF-1α sequences, ≥99.7% identity to the ex-type of G. smithogilvyi (ITS: JQ910642, 474 matching bp; TEF-1α: JQ910645, 335-338 matching bp), and for TUB2 sequences, ≥99.1% identity to G. castaneae (LN999975, 446-453 matching bp). Pathogenicity tests were carried out on surface disinfected nuts of Castanea sativa `Raigona´. A superficial wound was made in the pericarp of each nut. A 2-mm mycelial plug of a 7-days-old culture of G. smithogilvyiwas then inoculated: twenty nuts with isolate EFA924A and twenty with isolate EFA962.4A. Twenty nuts inoculated with sterile agar were used as control. The holes were sealed with Parafilm®. Nuts were incubated in a moist chamber at 22±2°C. Two replicated tests were carried out. Four inoculated and four control nuts were inspected for the presence and progress of rot symptoms every seven days. Three weeks after inoculation, all remaining inoculated nuts were completely rotted, whereas all control nuts remained healthy. Gnomoniopsis smitholgilvyi was reisolated from all inoculated nuts, and it was not recovered from the controls. This pathogen causes chestnut brown rot on sweet chestnut worldwide (EPPO, 2022), causing also shoot cankers on chestnut (Lione et al, 2019). This is the first report of G. smithogilvyi causing chestnut brown rot on nuts and burrs of C. sativa in Spain. Future studies on the incidence of this pathogen and its impact on chestnut yield should be carried out in the main European producing countries, i.e. Spain, Italy, Portugal and Greece, where the disease has been detected and represents an emerging threat to chestnut production.

The Legitimate Name of a Fungal Plant Pathogen and the Ethics of Publication in the Era of Traceability.

When more scientists describe independently the same species under different valid Latin names, a case of synonymy occurs. In such a case, the international nomenclature rules stipulate that the first name to appear on a peer-reviewed publication has priority over the others. Based on a recent episode involving priority determination between two competing names of the same fungal plant pathogen, this letter wishes to open a discussion on the ethics of scientific publications and points out the necessity of a correct management of the information provided through personal communications, whose traceability would prevent their fraudulent or accidental manipulation.