First report of Fusarium concentricum causing fruit blotch on roselle (Hibiscus sabdariffa)

First record of Fusarium concentricum (Hypocreales: Hypocreaceae) isolated from the moth Polychrosis cunninhamiacola (Lepidoptera: Tortricidae) as an entomopathogenic fungus

Fusarium concentricum Nirenberg & O' Donnell (Ascomycota: Hypocreales) is a fungal species known to infect plants, but never reported as entomopathogenic. Polychrosis cunninhamiacola Liu et Pei (Lepidoptera: Tortricidae: Olethreutinae) is a major and widespread insect pest causing economic losses to cultivated Chinese fir Cunninghamia lanceolata (Lamb.) Hook. It is routinely controlled by extensive use of chemical insecticides, which is perceived as environmentally unsustainable. During March and April of 2019-2020, muscardine cadavers of larvae and pupae of P. cunninhamiacola infected with growing fungus were collected in a fir forest in northern Guangdong Province, China. Conidia were isolated and cultured on PDA medium, from which the fungal strain was identified as F. concentricum FCPC-L01 by morphology and by sequence alignment match with Tef-1α gene. Pathogenicity bioassays at the conidial concentration 1 × 107 revealed P. cunninhamiacola adults and Danaus chrysippus (L.) (Lepidoptera: Nymphalidae) larvae are sensitive to the fungal infection, but not the fire ant Solenopsis invicta Buren (Hymenoptera: Formicidae). We believe results indicate this fungal strain might be applicable against specific target insect pests. As this is the first record of a natural infection caused by F. concentricum in insects, we propose host specificity tests should be done to evaluate its potential as a biocontrol agent.

First report on molecular identification of Fusarium species causing fruit rot of mandarin ( Citrus reticulata) in Bangladesh

Background: Fusarium rot is a newly introduced, devastating disease of citrus fruits. The current investigation was undertaken to characterize the microbes responsible for fruit rot in Citrus reticulata. Methods: Pathogens were isolated from infected citrus fruits using morphological and molecular approaches. For confirmation of the isolated fungi, polymerase chain reaction (PCR) amplification and internal transcribed spacer gene sequencing techniques were used. Results: The isolated fungus was grown on potato dextrose agar for three days and it produced clamydospores, hyphae and macroconidia. PCR amplification of isolated fungal DNA gave a 650 bp product. The sequence obtained from isolated fungi had 99.42% similarity with the reference Fusarium concentricum sequence in NCBI GenBank. The obtained sequence was deposited in GenBank (Accession No. MT856371). Two isolates showed virulence capability on fresh guava, sweet orange and tomato fruits, which confirmed species identification and Koch's postulates. Artificially inoculated fungal species grown on tested fruits showed typical Fusarium species symptoms. Conclusions: Outcomes of the present study are beneficial for the detection of this detrimental disease in postharvest Citrus reticulata fruits. Further research is needed for the control of this economically important disease. This is the first study of fruit rot in Citrus reticulata caused by Fusarium in Bangladesh.

First report on molecular identification of Fusarium species causing fruit rot of mandarin ( Citrus reticulata) in Bangladesh

Background: Fusarium rot is a newly introduced, devastating disease of citrus fruits. The current investigation was undertaken to characterize the microbes responsible for fruit rot in Citrus reticulata. Methods: Pathogens were isolated from infected citrus fruits using morphological and molecular approaches. For confirmation of the isolated fungi, polymerase chain reaction (PCR) amplification and internal transcribed spacer gene sequencing techniques were used. Results: The isolated fungus was grown on potato dextrose agar for three days and it produced clamydospores, hyphae and macroconidia. PCR amplification of isolated fungal DNA gave a 650 bp product. The sequence obtained from isolated fungi had 99.42% similarity with the reference Fusarium concentricum sequence in NCBI GenBank. The obtained sequence was deposited in GenBank (Accession No. MT856371). Two isolates showed virulence capability on fresh guava, sweet orange and tomato fruits, which confirmed species identification and Koch's postulates. Artificially inoculated fungal species grown on tested fruits showed typical Fusarium species symptoms. Conclusions: Outcomes of the present study are beneficial for the detection of this detrimental disease in postharvest Citrus reticulata fruits. Further research is needed for the control of this economically important disease. This is the first study of fruit rot in Citrus reticulata caused by Fusarium in Bangladesh.

First report of Fusarium concentricum as a causal agent of Fusarium leaf blotch on pecan (Carya illinoinensis) in Southeast China

The economically important nut crop pecan (Carya illinoinensis (Wangenh.) K. Koch) is seriously affected by increasing incidence of fungal disease worldwide (Xiao et al 2021). The top leaves of the pecan variety 'Pawnee' in the orchard of Zhejiang A&F University, Zhejiang, China were damaged by massive dark brown plaques in summer to autumn 2021. The causal agent was isolated from leaves with target plaques following the steps: sterilized with 70% alcohol (30 s × 2), rinsed with sterilized water (3 ×) before and after 5% sodium hypochlorite (30 s), excised the plaques, and placed on PDA medium at 28℃ in a dark incubator for 3-d. The mycelium on the edge of each colony was transferred to fresh SNA medium in dark for 2 weeks to induce conidia formation. A few conidia-germinated mycelia were transferredand inoculated on new plates containing fresh PDA medium to obtain the purified cultures. Koch's postulates were applied to validate the pathogenicity of the purified isolates. Non-woundedly healthy leaves (disinfected with 5% sodium hypochlorite) of 'Pawnee' seedlings were inoculated with 5 mm 7-d old purified cultures. Dark-brown spots appeared on the leaves 2 days post inoculation at 25℃. The spots became larger accompanied by partially cracking and slight deformation of inoculated leaves from day 2 to day 4, while the control leaves remained asymptomatic. A re-isolated strain ZJ-6 from these infected leaves was identified as the pathogenic isolate with the same symptom as the previous one. Morphologically, aerial mycelia of the pathogenic isolate ZJ-6 cashmere and white. The reverse of colony orange. The edge of the colony appeared gradually thinner, the aerial mycelia loose and flocky, and the matrix mycelium whitened. Hyphae were septate, translucent with smooth wall and 1.47-7.14 µm in width. Microconidia (n = 20) obovoid to fusoid, mainly with 0-septate, 4.45-7.78×4.79-16.25 µm. Macroconidia (n = 20) sickle, mainly with 3-5 septa, 5.56-10.28×56.67-114.54 µm. Simultaneous of monophialidic and polyphialidic conidiophores. Conidiophore width 1.47-3.68 µm, slightly smaller than vegetative hyphae. The morphological characteristics matched with previous descriptions of Fusarium species (Nirenberg and O'Donnell 1998; Wang et al 2013). The identity of ZJ-6 was confirmed by phylogenetic reconstruction using the concatenated sequences of the ATP citrate lyase (ACL1), Calmodulin (CaM), the internal transcribed spacer (ITS) rDNA region, ribosomal RNA gene (LSU), the largest subunit of DNA-dependent RNA polymerase II (RPB1), partial translation elongation factor-1 alpha (TEF) and β-Tubulin (TUB). To this end, the genomic DNA of ZJ-6 was extracted by the M5 hipermix-MF859 (Mei5 Biotechnology) and submitted to GenBank under the accession numbers OP933646, OP933647, OP925890, OP925889, OP933396, OP933648, and OP933397, respectively. The obtained sequences of ZJ-6 were used for nucleotide BLAST against thetandard databases, respectively, and the strains with sequence identification values above 98% were selected to construct multiple alignment for building a phylogenetic tree. This analyses allowed the identification of ZJ-6 as Fusarium concentricum Nirenberg & O'Donnell, a species with few reports that can cause serious damage to the fruits and branches of other hosts (Hasan et al 2020; Huda-Shakirah et al 2020; Wang et al 2013). This is the first report of pathogenic F. concentricum on pecan in Southeast China that caused no harvest of infected plants.

Fusarium spp. Associated with Dendrobium officinale Dieback Disease in China

A rare plant species of the Orchidaceae family, Dendrobium officinale is considered among the top ten Chinese medicinal herbs for its polysaccharide. Since 2021, when the dieback disease of D. officinale was first reported in Yueqing City, Zhejiang Province, China, Fusarium isolates (number = 152) were obtained from 70 plants in commercial greenhouses. The disease incidence ranged from 40% to 60% in the surveyed areas. Multilocus sequence analysis (MLSA) coupled with morphological characterization revealed that the collected isolates belonged to five species (sp.), viz., Fusarium concentricum, F. fujikuroi, F. nirenbergiae, F. curvatum, and F. stilboides, with isolation frequencies of 34.6%, 22.3%, 18.4%, 13.8%, and 10.5%, respectively. Notably, at least two Fusarium species were simultaneously isolated and identified from the infected plants. Finally, the pathogenicity test results demonstrated that such species were responsible for the dieback disease of D. officinale. However, F. concentricum and F. fujikuroi were more invasive compared to the other species in this study. To the best of the authors’ knowledge, this study was the first report of F. concentricum, F. curvatum, F. fujikuroi, F. nirenbergiae, and F. stilboides causing the dieback disease of D. officinale in China and worldwide. This work provides valuable data about the diversity and pathogenicity of Fusarium populations, which will help in formulating effective strategies and policies for better control of the dieback disease.