Abstract
Increasing recognition of novel Phaeoacremonium species, and their recent taxonomic reassignment through phylogeny based on the β-tubulin and actin genes, have highlighted the presence of paraphyly, intraspecific variation, and incongruence of some Phaeoacremonium species. This study investigated the intergenic spacer rDNA regions of a representative collection of 31 Phaeoacremonium italicum strains, and compared their structures with those of the closest related species, Phaeoacremonium alvesii and Phaeoacremonium rubrigenum. These intergenic spacer sequences had five categories of repeat elements that were organised into distinct patterns. Morphological analyses of the P. italicum strains provided a more detailed description of P. italicum. The phylogenetic tree constructed using the intergenic spacer sequences compared with that obtained by combined analysis of β-tubulin and actin sequences indicated that the intergenic spacer rDNA region distinguished intraspecific and interspecific variations. Further molecular studies are required to determine whether intergenic spacer sequences can improve precision in defining Phaeoacremonium phylogeny, and prevent misidentification and the introduction of vague species boundaries for the genus.
Highlights
The genus Phaeoacremonium (Togniniales, Togniniaceae) was originally described in 1996, containing only six species (Crous et al, 1996)
The present study aimed to investigate the structure of the IGS ribosomal DNA (rDNA) regions of a representative collection of P. italicum strains as a study model, and to compare them with strains of the closely related species P. alvesii and P. rubrigenum, to emphasise intraspecific and interspecific genetic variations
The BLAST search and the comparison of the β-tubulin and actin sequences with the reference strains as ex-type allowed the 49 Italian strains to be attributed to 11 Phaeoacremonium spp., as follows: P. amygdalinum, P. croatiense, P. fraxinopennsylvanicum, P. iranianum, P. italicum (30), P. minimum, P. oleae, P. parasiticum, P. scolyti, P. sicilianum and P. viticola (Table 1)
Summary
The genus Phaeoacremonium (Togniniales, Togniniaceae) was originally described in 1996, containing only six species (Crous et al, 1996). 13 Phaeoacremonium species have been associated with olive trees, and 34 with fruit trees, of which ten were on olive and 18 were on fruit trees in Europe and Mediterranean countries (Crous and Gams, 2000; Mostert et al, 2006; Nigro et al, 2013; Carlucci et al, 2015; Gramaje et al, 2015; Soltaninejad et al, 2017; Spies et al, 2018; Sohrabi et al, 2020)
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