First Report of Fusarium equiseti Causing a Sheath Rot of Corn in China

Identification, Pathogenicity, and Genetic Diversity of Fusarium spp. Associated with Maize Sheath Rot in Heilongjiang Province, China

Maize sheath rot is a prevalent maize disease in China. From 2020 to 2021, symptomatic samples were collected from the main maize-growing regions of Heilongjiang province. To clarify the population and genetic diversity, as well as the virulence of pathogens responsible for maize sheath rot, a total of 132 Fusarium isolates were obtained and used for follow-up studies. Ten Fusarium species were identified based on morphological characteristics, and phylogenetic analysis was conducted using the TEF-1α gene sequences, including F. verticillioides (50.00%), F. subglutinans (18.94%), the Fusarium incarnatum-equiseti species complex (14.39%), F. temperatum (5.30%), F. acuminatum (3.03%), F. solani (2.27%), F. sporotrichioides (2.27%), F. tricinctum (1.52%), F. asiaticum (1.52%), and F. proliferatum (0.76%). All 10 Fusarium species could produce oval-to-annular lesions on maize sheath, and the lesions were grayish yellow to dark brown in the center and surrounded by a dark gray-to-dark brown halo. Of these, F. tricinctum and F. proliferatum showed significantly higher virulence than the other Fusarium species. In addition, haplotype analysis based on the concatenated sequences of the ITS and TEF-1a genes showed that 99 Fusarium isolates which belonged to the Fusarium fujikuroi species complex—consisting of F. verticillioides isolates, F. subglutinans isolates, F. temperatum isolates, and F. proliferatum isolates—could be grouped into 10 haplotypes, including 5 shared haplotypes (Haps 1, 2, 4, 5, and 6) and 5 private haplotypes (Haps 3, 7, 8, 9, and 10). Furthermore, the F. verticillioides clade in the haplotype network was radial with the center of Hap 2, suggesting that population expansion occurred. This research showed that Fusarium species associated with maize sheath rot in Heilongjiang province are more diverse than previously reported, and this is the first time that F. subglutinans, F. temperatum, F. solani, F. sporotrichioides, F. tricinctum, and F. acuminatum have been confirmed as the causal agents of maize sheath rot in Heilongjiang province.

Identification and First Report of Fusarium andiyazi Causing Sheath Rot of Zizania latifolia in China

Zizania latifolia is a perennial plant native to East Asia. The swollen culm of Z. latifolia is a popular vegetable and traditional herbal medicine consumed in China and some other Asian countries. From 2019 to 2021, a sheath rot disease was found in Zhejiang Province of China. Symptoms mainly occurred in the leaf sheath showing as brown necrotic lesions surrounded by yellow halos. The pathogen fungal isolates were isolated from the affected sheaths. Ten representative isolates were selected for morphological and molecular identification by phylogenetic analyses of the translation elongation factor 1-α (TEF1) and the RNA polymerase II subunit beta (RPB2) gene regions. Based on the combined datasets, the fungal isolates were identified as Fusarium andiyazi. Koch’s postulates were confirmed by pathogenicity test, re-isolation and re-identification of the fungal isolates. To the best of our knowledge, this is the first report of sheath rot caused by F. andiyazi in Z. latifolia in China.

Identification of a new Talaromyces strain DYM25 isolated from the Yap Trench as a biocontrol agent against Fusarium wilt of cucumber

Fusarium equiseti is a pathogenic fungus of plant root rot, and there are few studies on the biocontrol strains of plant wilt caused by F. equiseti. Hence, we conducted a screening and antimicrobial characterization study of marine-origin biocontrol fungi from water samples of the Yap Trench. A new Talaromyces strain DYM25 was screened from water samples of the Yap Trench in the western Pacific Ocean, and its potential as a biocontrol agent against Fusarium wilt of cucumber was studied. 18S rRNA and ITS gene sequencing verified that strain DYM25 belongs to the genus Talaromyces. The growth of F. equiseti was inhibited by strain DYM25 through the antibiosis effect. A preliminary test was first conducted to examine the bioactive stability of filtered DYM25 broth against F. equiseti under various conditions, including high temperature, UV light, alkaline environment, and the presence of metal ions, which indicated its potential as a bio-control agent. The results of the pot experiment showed that F. equiseti caused cucumber wilt, which could be mitigated using the fermentation broth of strain DYM25 (52.9 %). On the other hand, the alkaloid chromogenic reaction showed that the alkaloid salts present in the crude n-butanol extracts were most likely the major components that might have an antimicrobial effect. Therefore, Talaromyces sp. DYM25 represents a new species that can be used as a novel biocontrol agent against cucumber wilt.

Fusarium incarnatum-equiseti Species Complex Causing Root Rot Disease on Leymus chinensis in China

Leymus chinensis (Trin.) Tzvel. is a rhizomatous grass widely grown in the grasslands of Eurasia. With strong fertility and stress resistance, L. chinensis makes an excellent pasture and mowing grass, contributing to animal husbandry and thus playing an important role in the local economy of the northern grassland area in China (Baoyin et al. 2014). During August to September 2019, diseased roots of L. chinensis were collected from an artificially planted grassland (40°47'44" N, 111°43'58″ E, alt. 1049 m) in Shaerqin County, Hohhot, China. Infected plants were scattered across the field with disease incidence up to 2%. Symptoms observed were wilted plants and rotten roots. In order to identify the causal pathogen of root rot on L. chinensis, symptomatic pieces (5 × 5 mm) of grass roots were excised and surface sterilized with 75% ethanol for 3-5 s followed by 1% NaClO for 2-3 min, rinsed three times with sterile distilled water, and placed on water agar and incubated at 25°C for 3 days. The mycelia were cut and transferred onto potato dextrose agar (PDA) for subculture. A fungus was consistently isolated, and a strain, named LCH054, was obtained by hyphal tip culture. Culture developed as white and fluffy aerial mycelia, with diffused pink pigment on the reverse side of PDA after culturing at 25℃ for 7 days. A culture of LCH054 was transferred to carnation leaf agar (CLA) (Li et al. 2014) and incubated at 25°C for 10 days. Microconidia were absent but macroconidia were produced. Macroconidia were hyaline, sickle-shaped, and had 4 to 7 septa, 19.8 to 63.6 (mean 43.8) × 1.8 to 5.7 (mean 3.2) μm (n = 100). Chlamydospores were ellipsoidal or subglobose, with thick walls in clumps or chains. All morphological characteristics of LCH054 resembled Fusarium equiseti (Leslie and Summerell 2006). The primers of the internal transcribed spacer (ITS) region (White et al. 1990) and translation elongation factor 1α gene (TEF-1α) (O'Donnell et al. 1998) were used to amplify the isolate, and the fragments were sequenced. BLASTn search in the NCBI database using the ITS and TEF-1α sequences revealed 99 to 100% similarities with F. equiseti. BLAST analysis of the ITS and TEF-1α sequencies in the FUSARIUM-ID database showed them to have 99.21% (500 bp out of 504 bp) and 99.52% (622 bp out of 625 bp) similarities with the Fusarium incarnatum-equiseti species complex (FIESC) (strain NRRL 45997) (O'Donnell et al. 2009), respectively. The ITS and TEF1-α sequences were deposited in GenBank as accession numbers MT937067 and MT947530, respectively. The strain LCH054 was identified as a member of the FIESC based on morphological and molecular characteristics. For the pathogenicity test, one hundred of L. chinensis seeds were planted into five pots (12 cm [diameter]) × 15 cm [high]) and kept in a greenhouse under a 16-h photoperiod with temperatures of 20-25°C and 40% relative humidity. The conidial suspension of LCH054 was prepared by washing 7-day old fungal culture grown on CLA medium using sterile deionized water. Conidia were filtered through three layers of sterile cheese cloth, counted, and adjusted to 1 × 105 conidia/ml with a hemocytometer. Forty 1-month-old healthy plants (four pots) were inoculated with 400 ml of conidia suspension using the root drenching method, whereas the inoculum was replaced with 100 ml sterile water on control plants (one pot). Fourteen days after inoculation, all inoculated plants showed the typical symptoms of root rot identical to those observed in the field, whereas the control plants remained healthy. LCH054 was re-isolated from the inoculated plants and identified by the morphological and molecular approaches as described above. To the best of our knowledge, this is the first report of root rot caused by F. incarnatum-equiseti on L. chinensis in China as well as worldwide. The presence of the pathogen could cause significant economic losses in L. chinensis production. For this reason, strategies for the management and control of this disease should be developed and implemented.

Assembly and annotation of whole-genome sequence of Fusarium equiseti

Fusarium equiseti is a plant pathogen with a wide range of hosts and diverse effects, including probiotic effects. However, the molecular mechanisms underlying these effects remain unclear, hindering its effective utilization. The final assembly included 16 scaffolds of contiguous sequence without gaps. The total sequence length was 40,776,005 bp, and the GC content of 48.01%. In total, we annotated the putative function of 13,134 genes, accounting for 94.97% of the candidate genes. We identified two and 23 candidate genes that are likely involved in the production of mycotoxins zearalenone and trichothecene, respectively. A comparative genomic analysis supported the high quality of the F. equiseti assembly. Our comprehensive analysis of whole-genome sequence will serve as a valuable resource for future studies of expression, regulation, function and evolution of the genes of F. equiseti as well as studies into disease prevention and control.

Symptoms and pathogens diversity of Corn Fusarium sheath rot in Sichuan Province, China

To elucidate the symptoms and pathogens diversity of corn Fusarium sheath rot (CFSR), diseased samples were collected from 21 county-level regions in 12 prefecture-level districts of Sichuan Province from 2015 to 2018 in the present study. In the field, two symptom types appeared including small black spots with a linear distribution and wet blotches with a tawny or brown color. One hundred thirty-seven Fusarium isolates were identified based on morphological characteristics and phylogenetic analysis (EF1-α), and Koch's postulates were also assessed. The results identified the isolates as 8 species in the Fusarium genus, including F. verticillioides, F. proliferatum, F. fujikuroi, F. asiaticum, F. equiseti, F. meridionale, F. graminearum and F. oxysporum, with isolation frequencies of 30.00, 22.67, 15.33, 7.33, 6.00, 5.33, 3.33 and 1.33%, respectively. Fusarium verticillioides and F. proliferatum were the dominant and subdominant species, respectively. Two or more Fusarium species such as F. verticillioides and F. proliferatum were simultaneously identified at a mixed infection rate of 14.67% in the present study. The pathogenicity test results showed that F. proliferatum and F. fujikuroi exhibited the highest virulence, with average disease indices of 30.28 ± 2.87 and 28.06 ± 1.96, followed by F. equiseti and F. verticillioides, with disease indices of 21.48 ± 2.14 and 16.21 ± 1.84, respectively. Fusarium asiaticum, F. graminearum and F. meridonale showed lower virulence, with disease indices of 13.80 ± 2.07, 11.57 ± 2.40 and 13.89 ± 2.49, respectively. Finally, F. orysporum presented the lowest virulence in CFSR, with a disease index of 10.14 ± 1.20. To the best of our knowledge, this is the first report of F. fujikuroi, F. meridionale and F. asiaticum as CFSR pathogens in China.