Symptomatic Citrus trees reveal a new pathogenic lineage in Fusarium and two new Neocosmospora species

Epitypification of Fusarium oxysporum - clearing the taxonomic chaos

Fusarium oxysporum is the most economically important and commonly encountered species of Fusarium. This soil-borne fungus is known to harbour both pathogenic (plant, animal and human) and non-pathogenic strains. However, in its current concept F. oxysporum is a species complex consisting of numerous cryptic species. Identification and naming these cryptic species is complicated by multiple subspecific classification systems and the lack of living ex-type material to serve as basic reference point for phylogenetic inference. Therefore, to advance and stabilise the taxonomic position of F. oxysporum as a species and allow naming of the multiple cryptic species recognised in this species complex, an epitype is designated for F. oxysporum. Using multi-locus phylogenetic inference and subtle morphological differences with the newly established epitype of F. oxysporum as reference point, 15 cryptic taxa are resolved in this study and described as species.

Molecular systematics of two sister clades, the Fusarium concolor and F. babinda species complexes, and the discovery of a novel microcycle macroconidium-producing species from South Africa

Multilocus DNA sequence data were used to investigate species identity and diversity in two sister clades, the Fusarium concolor (FCOSC) and F. babinda species complexes. Of the 109 isolates analyzed, only 4 were received correctly identified to species and these included 1/46 F. concolor, 1/31 F. babinda, and 2/3 F. anguioides. The majority of the F. concolor and F. babinda isolates were received as F. polyphialidicum, which is a heterotypic synonym of the former species. Previously documented from South America, Africa, Europe, and Australia, our data show that F. concolor is also present in North America. The present study expands the known distribution of F. babinda in Australia to Asia, Europe, and North America. The molecular phylogenetic results support the recognition of a novel Fusarium species within the FCOSC, which is described and illustrated here as F. austroafricanum, sp. nov. It was isolated as an endophyte of kikuyu grass associated with a putative mycotoxicosis of cattle and from plant debris in soil in South Africa. Fusarium austroafricanum is most similar morphologically to F. concolor and F. babinda but differs from the latter two species in producing (i) much longer macroconidia in which the apical cell is blunt to slightly papillate and the basal cell is only slightly notched and (ii) macroconidia via microcycle conidiation on water agar. BLASTn searches of the whole genome sequence of F. austroafricanum NRRL 53441 were conducted to predict mycotoxin potential, using genes known to be essential for the synthesis of several mycotoxins and biologically active metabolites. Based on the presence of intact gene clusters that confer the ability to synthesize mycotoxins and pigments, we analyzed cracked corn kernel cultures of F. austroafricanum via liquid chromatography-mass spectrometry (LC-MS) but failed to detect these metabolites in vitro.

Fusarium metavorans sp. nov.: The frequent opportunist 'FSSC6'

The Fusarium solani species complex (FSSC) is the most common group of fusaria associated with superficial and life-threatening infections in humans. Here we formally introduce Fusarium metavorans sp. nov., widely known as FSSC6 (Fusarium solani species complex lineage 6), one of the most frequent agents of human opportunistic infections. The species is described with multilocus molecular data including sequences of internal transcribed spacer region (ITS), portions of the translation elongation factor 1-a gene (TEF1), and the partial RNA polymerase II gene (rPB2). A phylogenetic approach was used to evaluate species delimitation. Topologies of the trees were concordant. Phylogenetic analyses suggest that the FSSC consists of three major clades encompassing a large number of phylogenetic species; Fusarium metavorans corresponds to phylogenetic species 6 within FSSC clade 3. The species has a global distribution and a wide ecological amplitude, also including strains from soil and agents of opportunistic plant disease; it was also isolated from the gut of the wood-boring cerambycid beetle Anoplophora glabripennis.

Removing chaos from confusion: assigning names to common human and animal pathogens in Neocosmospora

The genus Neocosmospora encompasses highly prevalent and aggressive human and animal fungal pathogens. Here we assign formal descriptions and Latin binomials to some of the most clinically relevant phylogenetic species of the genus. Three new species, named Neocosmospora catenata, N. gamsii and N. suttoniana (previously assigned to the informal names 'Fusarium' solani species complex (FSSC) lineages, FSSC 43, FSSC 7 and FSSC 20, respectively) are described on the basis of multilocus phylogenetic analyses (using EF-1α, ITS, LSU and RPB2 loci) and morphological characters. Lineage FSSC 9 is conspecific with the ex-type strain of Cylindrocarpon tonkinense, thus the new combination Neocosmospora tonkinensis is proposed. In addition, and based on the latest taxonomy for this generic complex, new combinations are introduced for four medically important taxa: Neocosmospora keratoplastica, N. lichenicola, N. metavorans and N. petroliphila. The most significant distinctive features for all the clinically relevant species treated here are compared and illustrated.

Neocosmospora perseae sp. nov., causing trunk cankers on avocado in Italy

Trunk and branch cankers are among the most important diseases compromising avocado production worldwide. A novel species, Neocosmospora perseae sp. nov. is described isolated from trunk lesions on Persea americana in the main avocado producing area of Sicily, Italy. The new species is characterised using a polyphasic approach including morphological characters and a multilocus molecular phylogenetic analysis based on partial sequences of the translation elongation factor-1α, the internal transcribed spacer regions plus the large subunit of the rDNA cistron, and the RNA polymerase II second largest subunit. Pathogenicity tests and the fulfilment of Koch's postulates confirm N. perseae as a novel canker pathogen of Persea americana.

New Fusarium species from the Kruger National Park, South Africa

Three new Fusarium species, F. convolutans, F. fredkrugeri, and F. transvaalense (Ascomycota, Hypocreales, Nectriaceae) are described from soils collected in a catena landscape on a research supersite in the Kruger National Park, South Africa. The new taxa, isolated from the rhizosphere of three African herbaceous plants, Kyphocarpa angustifolia, Melhania acuminata, and Sida cordifolia, are described and illustrated by means of morphological and multilocus molecular analyses based on sequences from five DNA loci (CAL, EF-1 α, RPB1, RPB2 and TUB). According to phylogenetic inference based on Maximum-likelihood and Bayesian approaches, the newly discovered species are distributed in the Fusarium buharicum, F. fujikuroi, and F. sambucinum species complexes.

Two new species of the Fusarium solani species complex isolated from compost and hibiscus (Hibiscus sp.)

Two new species in the Fusarium solani species complex (FSSC) are described and introduced. The new taxa are represented by German isolates CBS 142481 and CBS 142480 collected from commercial yard waste compost and vascular tissue of a wilting branch of hibiscus, respectively. The phylogenetic relationships of the collected strains to one another and within the FSSC were evaluated based on DNA sequences of 6 gene loci. Due to the limited sequence data available for reference strains in GenBank, however, a multi-gene phylogenetic analysis included partial sequences for the internal transcribed spacer region and intervening 5.8S nrRNA gene (ITS), translation elongation factor 1-alpha (tef1) and the RNA polymerase II second largest subunit (rpb2). Morphological and molecular phylogenetic data independently showed that these strains are distinct populations of the FSSC, nested within Clade 3. Thus, we introduce Fusarium stercicola and Fusarium witzenhausenense as novel species in the complex. In addition, 19 plant species of 7 legume genera were evaluated for their potential to host the newly described taxa. Eighteen plant species were successfully colonized, with 6 and 9 of these being symptomatic hosts for F. stercicola and F. witzenhausenense, respectively. As plants of the family Fabaceae are very distant to the originally sourced material from which the new taxa were recovered, our results suggest that F. stercicola and F. witzenhausenense are not host-specific and are ecologically fit to sustain stable populations in variety of habitats.

Fusarium ershadii sp. nov., a Pathogen on Asparagus officinalis and Musa acuminata

Two Fusarium strains, isolated from Asparagus in Italy and Musa in Vietnam respectively, proved to be members of an undescribed clade within the Fusarium solani species complex based on phylogenetic species recognition on ITS, partial RPB2 and EF-1α gene fragments. Macro- and micro-morphological investigations followed with physiological studies done on this new species: Fusarium ershadii sp. nov can be distinguished by its conidial morphology. Both isolates of Fusarium ershadii were shown to be pathogenic to the monocot Asparagus officinalis when inoculated on roots and induced hollow root symptoms within two weeks in Asparagus officinalis seedlings. In comparison mild disease symptoms were observed by the same strains on Musa acuminata seedlings.

Emerging citrus diseases in Europe caused by species of Diaporthe

Species of Diaporthe are considered important plant pathogens, saprobes, and endophytes on a wide range of plant hosts. Several species are well-known on citrus, either as agents of pre- or post-harvest infections, such as dieback, melanose and stem-end rot on fruit. In this study we explored the occurrence, diversity and pathogenicity of Diaporthe species associated with Citrus and allied genera in European orchards, nurseries, and gardens. Surveys were carried out during 2015 and 2016 in Greece, Italy, Malta, Portugal, and Spain. A total of 79 Diaporthe strains were isolated from symptomatic twigs, branches and trunks. A multi-locus phylogeny was established based on five genomic loci (ITS, tef1, cal, his3 and tub2), and the morphological characters of the isolates determined. Preliminary pathogenicity tests were performed on lemon, lime, and orange plants with representative isolates. The most commonly isolated species were D. foeniculina and D. baccae, while only four isolates of D. novem were collected. Two new Diaporthe species, described here as D. limonicola and D. melitensis spp. nov. were found associated with a new devastating dieback disease of lemon plants. Furthermore, one cluster of sterile Diaporthe isolates was renamed as D. infertilis. Pathogenicity tests revealed most of the Citrus species as susceptible to D. baccae, D. foeniculina, and D. novem. Moreover, D. limonicola and D. melitensis caused serious cankers affecting all the Citrus species tested. This study is the first report of D. baccae and D. novem on citrus in Europe, and the first detection of a new Diaporthe canker disease of citrus in Europe. However, no isolates of D. citri were found. The study improves our understanding of the species associated with several disease symptoms on citrus plants, and provides useful information for effective disease management.

First report of Phyllosticta citricarpa and description of two new species, P. paracapitalensis and P. paracitricarpa, from citrus in Europe

The genus Phyllosticta occurs worldwide, and contains numerous plant pathogenic, endophytic and saprobic species. Phyllosticta citricarpa is the causal agent of Citrus Black Spot disease (CBS), affecting fruits and leaves of several citrus hosts (Rutaceae), and can also be isolated from asymptomatic citrus tissues. Citrus Black Spot occurs in citrus-growing regions with warm summer rainfall climates, but is absent in countries of the European Union (EU). Phyllosticta capitalensis is morphologically similar to P. citricarpa, but is a non-pathogenic endophyte, commonly isolated from citrus leaves and fruits and a wide range of other hosts, and is known to occur in Europe. To determine which Phyllosticta spp. occur within citrus growing regions of EU countries, several surveys were conducted (2015-2017) in the major citrus production areas of Greece, Italy, Malta, Portugal and Spain to collect both living plant material and leaf litter in commercial nurseries, orchards, gardens, backyards and plant collections. A total of 64 Phyllosticta isolates were obtained from citrus in Europe, of which 52 were included in a multi-locus (ITS, actA, tef1, gapdh, LSU and rpb2 genes) DNA dataset. Two isolates from Florida (USA), three isolates from China, and several reference strains from Australia, South Africa and South America were included in the overall 99 isolate dataset. Based on the data obtained, two known species were identified, namely P. capitalensis (from asymptomatic living leaves of Citrus spp.) in Greece, Italy, Malta, Portugal and Spain, and P. citricarpa (from leaf litter of C. sinensis and C. limon) in Italy, Malta and Portugal. Moreover, two new species were described, namely P. paracapitalensis (from asymptomatic living leaves of Citrus spp.) in Italy and Spain, and P. paracitricarpa (from leaf litter of C. limon) in Greece. On a genotypic level, isolates of P. citricarpa populations from Italy and Malta (MAT1-2-1) represented a single clone, and those from Portugal (MAT1-1-1) another. Isolates of P. citricarpa and P. paracitricarpa were able to induce atypical lesions (necrosis) in artificially inoculated mature sweet orange fruit, while P. capitalensis and P. paracapitalensis induced no lesions. The Phyllosticta species recovered were not found to be widespread, and were not associated with disease symptoms, indicating that the fungi persisted over time, but did not cause disease.