The taxonomy of the genus Colletotrichum has undergone tremendous changes over the last decade, with over 200 species being currently recognised and species complexes being informally used to cluster those species. Many of these species are important plant pathogens, some rather polyphagous and others host-specific, but several occur seldomly and some may in fact be ecologically endangered. Based mainly on literature from the past decade, in this work we review the occurrence, geographic distribution and host spectrum of currently recognised Colletotrichum species under phylogenetic, pathological/agronomic and ecological perspectives, providing a list arranged by Colletotrichum species and species complexes. A total of 257 species are listed and grouped into 15 species complexes. In this work we have recorded 1353 unique host species-Colletotrichum species association records from 720 hosts, with the Fabaceae as the family with higher number of hosts (52 host species) but with the Rosaceae as the family with the highest number of host species-Colletotrichum species association records (118 association records). According to occurrence data, 88 species are common in nature, 128 were considered as data deficient and 41 are threatened, some of which are likely extinct from nature and preserved only in culture collections. Several species are relevant plant pathogens, in some cases geographically confined and thus of potential quarantine relevance. Based on the major changes that occurred on Colletotrichum taxonomy over the last decade, this work provides a comprehensive overview of occurrence data of Colletotrichum species, compiling host range and geographical distribution, with relevance for plant pathology and conservation mycology. The current taxonomic framework in Colletotrichum is revealing numerous species but poses challenges to the employment of standard criteria for the evaluation of biological conservation of these fungi. We advocate that conservation mycology and taxonomy should find common routes simultaneously enabling the correct delimitation of species of Colletotrichum and the implementation of feasible criteria for the evaluation of conservation. The employment of new technologies, such whole genome sequencing (WGS), will help and support the description of new species and to gain a better understanding of the genetic bases of speciation processes.

Colletotrichum species and complexes: geographic distribution, host range and conservation status

Role of microbial diversity to influence the growth and environmental remediation capacity of bamboo: A review

The numbers of fungi: are the most speciose genera truly diverse?

Classification is the most important approach to cataloging biological diversity. It serves as a principal means of communication between scientific disciplines, as well as between scientis...

Stop the Abuse of Time! Strict Temporal Banding is not the Future of Rank-Based Classifications in Fungi (Including Lichens) and Other Organisms

Phyllosphere associated microorganisms play a crucial role in protecting plants from diseases, while their composition and diversity are strongly influenced by heavy metal contaminants. As dioecious plants exhibited sexual dimorphism in metal accumulation and tolerance between male and female individuals, in this study we used male and female full-sibs of Populus deltoides to investigate whether the two plant sexes will present sexual differences in the phyllosphere microbiome structure and associated pathogen resistance against a leaf pathogenic fungus after soil cadmium (Cd) exposure. We found that Cd-treated male plants grew better and accumulated more leaf Cd than females. Cd stress reduced leaf lesion area of both plant sexes after leaf pathogen infection, whereas male plants exhibited better resistance than females. More importantly, Cd exposure differentially altered the structure and function of phyllosphere microbiomes between male and female plants, with more abundant ecologically beneficial microbes but decreased pathogenic fungal taxa harbored in male plants. Further in vitro toxicity tests suggested that such sexual difference in pathogen resistance between the two plant sexes could attribute to direct Cd toxicity and indirect shifts in the phyllosphere microbiome. This study provides implication for understanding the underlying mechanism of heavy metals involved in plant-pathogen interactions.

Soil cadmium stress affects phyllosphere microbiome and associated pathogen resistance differently in male and female poplars.

Thaumatin-like proteins (TLPs) are involved in the plant defense response against pathogens, and most of them exhibit antifungal activity. However, the role of TLPs in pathogen-induced defense responses in spruce is not fully understood. In this study, four TLP genes encoding thaumatin-like protein, designated as PlTLP1–4, were isolated and identified from Picea likiangensis needles. Sequence analysis showed that PlTLP1, PlTLP3, and PlTLP4 contained 16 conserved cysteine residues, while PlTLP2 had only 10 conserved cysteine residues. qPCR analysis showed that PlTLPs were expressed in all tissues tested, PlTLP1, PlTLP3, and PlTLP4 had the highest expression levels in young fruits, while PlTLP2 had the highest expression levels in roots. In addition, the expression levels of four PlTLPs were significantly upregulated during infection by Lophodermium piceae. Four recombinant PlTLPs expressed in Escherichia coli exhibited obvious β-1,3-glucanase activity. The antifungal activity assay showed that four recombinant PlTLPs had significant inhibitory effects on the mycelial growth of L. piceae, Fusarium proliferatum, Botrytis cinerea, and Roussoella doimaesalongensis. Microscopic observation revealed that the recombinant PlTLP1–4 induced the morphological changes of the mycelia of L. piceae, and the recombinant PlTLP2 and PlTLP3 induced the morphological changes of the mycelia of F. proliferatum and R. doimaesalongensis, while all the recombinant PlTLPs had no obvious negative effect on the morphology of B. cinerea mycelium. These results suggest that PlTLP genes may play an important role in the defense response of P. likiangensis against L. piceae invasion.

Molecular Identification and Antifungal Properties of Four Thaumatin-like Proteins in Spruce (Picea likiangensis)

Phyllosphere-associated microbes play a crucial role in plant-pathogen interactions while their composition and diversity are strongly influenced by drought stress. As dioecious plant species exhibited secondary dimorphism between the two sexes in response to drought stress, whether such difference will lead to sex-specific differences in phyllosphere microbiome and associated pathogen resistance between male and female conspecifics is still unknown. In this study, we subjected female and male full siblings of a dioecious poplar species to a short period of drought treatment followed by artificial infection of a leaf pathogenic fungus. Our results showed that male plants grew better than females with or without drought stress. Female control plants had more leaf lesion area than males after pathogen infection, whereas drought stress reversed such difference. Further correlation and in vitro toxicity tests suggested that drought-mediated sexual differences in pathogen resistance between the two plant sexes could be attributed to the shifts in structure and function of phyllosphere-associated microbiome rather than the amount of leaf main defensive chemicals contained in plant leaves. Supportively, the microbiome analysis through high-throughput sequencing indicated that female phyllosphere enriched a higher abundance of ecologically beneficial microbes that serve as biological plant protectants, while males harbored abundant phytopathogens under drought-stressed conditions. The results could provide potential implications for the selection of suitable poplar sex to plants in drought or semi-drought habitats.

Drought stress mediated differences in phyllosphere microbiome and associated pathogen resistance between male and female poplars.

Cotton rose (Hibiscus mutabilis Linn.) is a deciduous shrub native to China. It has been widely cultivated in many provinces in China for its ornamental and ecological value (Shang et al., 2020). In May 2017, an unknown leaf spot symptom was first observed on H. mutabilis at the Chengdu Campus of Sichuan Agricultural University (30°42'31″ N, 103°51'28″ E). The disease occurred from May to September with approximately 81% incidence by field sample survey of 300 plants in Chengdu Greenway. The symptoms at first appeared as irregular black spots on the leaves. Then the lesions grew and coalesced into large, black necrotic areas, which later produced leaf chlorosis and abscission (Fig. 1-A). This disease seriously reduced the ornamental value of H. mutabilis. Forty diseased lesions (4 × 5 mm) were surface sterilized with 75% alcohol for 60 s and 3% NaClO for 45 s, rinsed three times in sterile water, placed onto potato dextrose agar (PDA), and then incubated in a dark at 25°C. From the 7 obtained isolates, 4 isolates exhibited the morphology described as Nigrospora oryzae (Hao et al., 2020). The fungus produced initially circular white colonies, and then the centers turned dark gray or black with age on the PDA. Hyphae were smooth, branched, septate, hyaline, or pale brown. Conidia (N = 100 spores) were abundant, and were solitary, dark-brown to black, smooth, aseptate, and measured 11 to 15 μm in diameter (Fig. 1). DNA was extracted from the fungal colonies using a DNeasyTM Plant Mini Kit (Qiagen). The internally transcribed spacer (ITS), β-tubulin gene (TUB), and translation elongation factor 1-alpha (TEF1) were amplified with primers ITS1/ITS4 (White et al., 1990), BT2A/BT2B (Glass and Donaldson 1995), and EF1-728F/EF1-986R (O'Donnell et al., 1998; Carbone and Kohn 1999), respectively. BLAST results indicated that the ITS, TUB, and TEF1 sequences (GenBank accession Nos. MN515070, MN733956, and MN635723, respectively) had 99% identity with N. oryzae sequences (GenBank accession Nos. KX986031, KY019553, and KY019358). The result was confirmed by multilocus phylogenetic analysis (Fig. 2). The morphological characteristics and molecular analyses of the isolate matched the description of N. oryzae. To confirm pathogenicity, Koch's postulates were fulfilled under controlle conditions. The seedlings of 20 two-year-old potted H. mutabilis plants were inoculated by spraying conidial suspension at the concentration of 1 × 106 conidia/ml on both sides of leaves. Sterilized distilled water (20 seedlings) were used as negative controls. The experiment was performed three times. All plants were incubated at 25°C ± 2°C under a 16 h/8 h photoperiod and 70%-75% relative humidity (RH) after inoculation, and observed daily for disease development. Two weeks later, the inoculated plants showed the same symptoms as the original diseased plants and the controls remained asymptomatic. The pathogen N. oryzae was re-isolated from all ioculated plants, and the culture and fungus characteristics were the same as those of the original isolate. But N. oryzae was not isolated from the control plants. The results indicated that N. oryzae is a causal agent of the disease. N. oryzae was reported as a leaf pathogen on cotton (Zhang et al., 2012), but this is the first report of N. oryzae causing leaf black spot on H. mutabilis in the world. The identification could provide relevant information for adopting appropriate management strategies to control the disease.

https://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-08-20-1796-PDN

Nigrospora oryzae Causing Black Leaf Spot Disease of Hibiscus mutabilis in China.

Defensins, as part of the PR protein family, not only have antimicrobial activity in vitro, but also play an important role in plant disease resistance. To explore the molecular function of defensin in spruce, a defensin gene PaDef was isolated and characterized from Picea asperata. The full-length cDNA sequence of the PaDef was 264 bp and contained an ORF of 252 bp, encoding a total of 83 amino acids. The deduced PaDef protein belongs to the gamma-thionin family and contains the Knot1 domain and eight conserved cysteine residues. Blast and phylogenetic analysis showed that the PaDef protein shared high homology with other plant defensin proteins. The tertiary structure of PaDef was obtained by homologous modelling using the structure of Pinus sylvestris defensin as a template and exhibited a βαββ structure. SDS-PAGE analysis showed that the molecular mass of recombinant PaDef expressed in Escherichia coli was 23.8 kDa. Plate assay showed that purified PaDef exhibited strong antifungal activity inhibiting the growth of Pestalotiopsis neolitseae, but not Colletotrichum gloeosporioides and Botrytis cinerea. Microscopic observation revealed that purified PaDef had a negative effect on the hyphal morphology of all three phytopathogens. qRT-PCR analysis indicated that the PaDef gene had the highest expression level in needles of P. asperata compared with roots, phloem, twigs, and could be significantly upregulated by the pathogenic fungus Lophodermium piceae, which causes needle cast disease. These results provide a molecular basis for determining the molecular function of defensin PaDef in P. asperata and its potential as an antifungal agent.

Molecular Identification and Antifungal Activity of a Defensin (PaDef) from Spruce

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