Untargeted metabolomic analyses support the main phylogenetic groups of the common
plant-associated Alternaria fungi isolated from grapevine (Vitis vinifera)
Alternaria , a cosmopolitan fungal genus is a dominant member of the grapevine ( Vitis
vinifera ) microbiome. Several Alternaria species are known to produce a variety of
secondary metabolites, which are particularly relevant to plant protection and food
safety in field crops. According to previous findings, the majority of Alternaria
species inhabiting grapevine belong to Alternaria sect. Alternaria . However, the
phylogenetic diversity and secondary metabolite production of the distinct Alternaria
species has remained unclear. In this study, our aim was to examine the genetic and
metabolic diversity of endophytic Alternaria isolates associated with the above-ground
tissues of the grapevine. Altogether, 270 Alternaria isolates were collected from
asymptomatic leaves and grape clusters of different grapevine varieties in the Eger
wine region of Hungary. After analyses of the nuclear ribosomal DNA internal transcribed
spacer (ITS) and RNA polymerase second largest subunit ( rpb2 ) sequences, 170 isolates
were chosen for further analyses. Sequences of the Alternaria major allergen gene
( Alt a 1 ), endopolygalacturonase ( endoPG ), OPA10-2, and KOG1058 were also included
in the phylogenetic analyses. Identification of secondary metabolites and metabolite
profiling of the isolates were performed using high-performance liquid chromatography
(HPLC)–high-resolution tandem mass spectrometry (HR-MS/MS). The multilocus phylogeny
results revealed two distinct groups in grapevine, namely A . alternata and the A
. arborescens species complex (AASC). Eight main metabolites were identified in all
collected Alternaria isolates, regardless of their affiliation to the species and
lineages. Multivariate analyses of untargeted metabolites found no clear separations;
however, a partial least squares-discriminant analysis model was able to successfully
discriminate between the metabolic datasets from isolates belonging to the AASC and
A. alternata . By conducting univariate analysis based on the discriminant ability
of the metabolites, we also identified several features exhibiting large and significant
variation between A. alternata and the AASC. The separation of these groups may suggest
functional differences, which may also play a role in the functioning of the plant
microbiome.
