Natural occurrence of trichothecene-producing Fusaria isolated from India with particular reference to sorghum

Fusarium and allied fusarioid taxa (FUSA). 1

Seven Fusarium species complexes are treated, namely F. aywerte species complex (FASC) (two species), F. buharicum species complex (FBSC) (five species), F. burgessii species complex (FBURSC) (three species), F. camptoceras species complex (FCAMSC) (three species), F. chlamydosporum species complex (FCSC) (eight species), F. citricola species complex (FCCSC) (five species) and the F. concolor species complex (FCOSC) (four species). New species include Fusicolla elongata from soil (Zimbabwe), and Neocosmospora geoasparagicola from soil associated with Asparagus officinalis (Netherlands). New combinations include Neocosmospora akasia, N. awan, N. drepaniformis, N. duplosperma, N. geoasparagicola, N. mekan, N. papillata, N. variasi and N. warna. Newly validated taxa include Longinectria gen. nov., L. lagenoides, L. verticilliforme, Fusicolla gigas and Fusicolla guangxiensis. Furthermore, Fusarium rosicola is reduced to synonymy under N. brevis. Finally, the genome assemblies of Fusarium secorum (CBS 175.32), Microcera coccophila (CBS 310.34), Rectifusarium robinianum (CBS 430.91), Rugonectria rugulosa (CBS 126565), and Thelonectria blattea (CBS 952.68) are also announced here. Citation: Crous PW, Sandoval-Denis M, Costa MM, Groenewald JZ, van Iperen AL, Starink-Willemse M, Hernández-Restrepo M, Kandemir H, Ulaszewski B, de Boer W, Abdel-Azeem AM, Abdollahzadeh J, Akulov A, Bakhshi M, Bezerra JDP, Bhunjun CS, Câmara MPS, Chaverri P, Vieira WAS, Decock CA, Gaya E, Gené J, Guarro J, Gramaje D, Grube M, Gupta VK, Guarnaccia V, Hill R, Hirooka Y, Hyde KD, Jayawardena RS, Jeewon R, Jurjević Ž, Korsten L, Lamprecht SC, Lombard L, Maharachchikumbura SSN, Polizzi G, Rajeshkumar KC, Salgado-Salazar C, Shang Q-J, Shivas RG, Summerbell RC, Sun GY, Swart WJ, Tan YP, Vizzini A, Xia JW, Zare R, González CD, Iturriaga T, Savary O, Coton M, Coton E, Jany J-L, Liu C, Zeng Z-Q, Zhuang W-Y, Yu Z-H, Thines M (2022). Fusarium and allied fusarioid taxa (FUSA). 1. Fungal Systematics and Evolution 9: 161-200. doi: 10.3114/fuse.2022.09.08.

First Report of Maize Stalk Rot Caused by Fusarium nelsonii in China

Maize (Zea Mays L.) is one of the main crops in Ningxia Province, China, and stalk rot has become a serious disease of maize in this area. Infected plants showed softening of the stalks at lower internodes, which lodged easily and died prematurely during grain filling, and the pith tissue internally appeared to be disintegrating and slightly brown to reddish. In September 2018, symptomatic tissue was collected from seventeen locations in Ningxia. The incidence ranged from 5% to 40% in surveyed fields, reaching as high as 86% in certain plots. The discolored stalk pith tissues from the lesion region were cut into small pieces (approximately 0.5 × 0.2 cm), superficially disinfected with 75% ethanol for 1 min and rinsed three times with sterile water before plating on potato dextrose agar (PDA) medium with chloromycetin. The purified strains were obtained by single-spore separation and transferred to PDA and carnation leaf agar (CLA) medium. Morphological and molecular characteristics confirmed the presence of nine Fusarium species in these samples, including Fusarium graminearum species complex and Fusarium verticillioides. Four isolates of Fusarium nelsonii were recovered from samples collected in Shizuishan and Wuzhong. On PDA plates, the floccose to powdery, white to rose-colored aerial mycelia were produced and covered plates after 8 days of incubation, producing abundant mesoconidia and chlamydospores. Mesoconidia were fusiform or lanceolate until slightly curved with 0-3 septa, and chlamydospores were initially smooth and transparent, and became verrucous and light brown. Macroconidia produced in CLA were straight or curved and falcate, usually having 3-5 septa, with beak-shaped strongly curved apical cells and foot-shaped basal cells. Two isolates (SS-1-7 and ZY-2-2) were selected for molecular identification, and the total DNA was extracted using a fungal genomic DNA separation kit (Sangon Biotechnology, Shanghai, China). Sequence comparison of EF-1α (GenBank accession numbers MW294197 and MW294198) and RPB2 (Accession MW294176 and MW294177) genes showed 97% homology with the sequences of F. nelsonii reported in GenBank (accession MN120760 for TEF and accession MN120740 for RPB2). Pathogenicity tests with two isolates (SS-1-7 and ZY-2-2) were performed by individually inoculating five 10-leaf stage maize plants at between the 2nd and 3rd stem nodes from the soil level with 20 μl conidial suspension at a concentration of 106 conidia/ml as described by Zhang et al. (2016). Five maize plants inoculated with sterile water were used as controls. The inoculated plants were kept at 25 ± 0.5°C in the greenhouse with a photoperiod of 12 h. After 30 days, all plants inoculated with the conidial suspension formed an internal dark brown necrotic area around the inoculation site, whereas the control plants showed no symptoms. The pathogen was re-isolated from the necrotic tissue of the inoculated plants and identified by morphological characteristics as F. nelsonii. This species was first described by Marasas et al. (1998), and it is expanding its host range and has been isolated from sorghum, Medicago, wheat, and cucumber (Ahmad et al. 2020). The pathogen should be paid more attention owing to a serious risk of trichothecene and aflatoxin contamination (Astoreca et al. 2019; Lincy et al. 2011). To our knowledge, this is the first report of maize stalk rot caused by F. nelsonii in China. References: Ahmad, A., et al. 2020. Plant disease.1542 https://doi.org/10.1094/PDIS-11-19-2511-PDN Astoreca, A. L., et al. 2019. Eur. J. Plant Pathol. 155:381. Lincy, S. V., et al. 2011. World J. Microbiol. Biotechnol. 27:981. Marasas, W. F. O., et al. 1998. Mycologia 90:505. Zhang, Y., et al. 2016. PLoS Pathog. 12:e1005485. Funding: This research was financially supported by National R & D Plan of China (No.2019QZKK0303); Ningxia Agriculture and Forestry Academy Science and Technology Cooperation Project (DW-X-2018019).

First report of Fusarium lacertarum causing Fusarium Head Blight on sorghum in North Carolina

In August 2018, sorghum plants (Sorghum bicolor (L.) Moench) from research field plots in Wake County, North Carolina were observed with head blight symptoms including panicles with red lesions, visible mycelium, and necrosis. At the time of collection, all plants in research plots displayed symptoms of Fusarium head blight and panicles averaged 33% area affected by symptoms and signs. From these affected plants, samples (n = 5) were collected for further identification. Symptomatic grains were surface sterilized for one minute in 0.825% sodium hypochlorite solution and rinsed for one minute in sterile, deionized water. After drying on sterile paper towels, grains were plated onto water agar. Resulting fungal hyphal tips were then transferred to antibiotic-amended potato dextrose agar (PDA) and incubated at 25oC. Cultures were incubated for 3 to 5 days. Isolates had abundant white hyphae accompanied with peach-colored pigment production. Macroconidia with 5-6 septations were 23.47 ± 7.74 µm long and 3.47 ± 0.66 µm wide with foot-shaped basal cells, tapering to hooked apical cells. Chlamydospores were present in chains but microconidia were not present. Morphological species recognition (MSR) criteria tentatively identified the isolate as Fusarium lacertarum Subrahm., in the Fusarium incarnatum-equiseti species complex (FIESC) using characteristics described by Leslie and Summerell 2006. Molecular characterization using translation elongation factor 1α (TEF-1 α, primers EF1 and EF2 from O'Donnell et al. 1998), β tubulin (TUB2, primers T1 and T22 from O'Donnell and Cigelnik 1997), and ribosomal protein subunit II (RPB2, primers 5F2 and 11AR from Cerón-Bustamante et al. 2018) was conducted to confirm morphological identification. DNA from the hyphae of pure cultures was extracted using the DNeasy PowerSoil DNA extraction kit according to manufacturer's guidelines. DNA amplification conditions followed the protocols for each primer set (O'Donnell et al. 1998; O'Donnell and Cigelnik 1997; Cerón-Bustamante et al. 2018). BLASTn analysis of TEF-1α (Isolate Accession MT149915, 573bp) alignment had 99.8% identity to F. lacertarum (NCBI accession: JF740828), TUB2 (Isolate Accession MT149914, 1,183bp) alignment had 99.3% identity to F. equiseti (NCBI accession: KJ396338), and RPB2 (Isolate Accession MT184173, 1,538bp) concatenated sequences had 95.3% identity to F. lacertarum (NCBI accession: MH582185). The TUB2 region most closely aligns to F. equiseti, which is likely due to an absence of TUB2 sequences labeled for F. lacertarum in the NCBI database. Pathogenicity was confirmed by spray-inoculating Southern Harvest 80G4 sorghum panicles (n = 9) at anthesis with four ml of conidial suspension (3.3×104 conidia/ml). Control plants (n = 9) were sprayed with sterile water. Plastic bags were placed around panicles for 24 hours to ensure moist conditions during the infection period. Plants were maintained in a greenhouse under a 12-hour light cycle and fertilized bi-weekly with 20-20-20 fertilizer. Symptoms were observed on inoculated panicles after 14 days, and the F. lacertarum isolate was recovered from inoculated plants and confirmed using methods described above. Fusarium spp. were not re-isolated from non-inoculated control plants. Members of FIESC are known to contribute to the Fusarium Head Blight disease complex and may be capable of producing mycotoxins associated with infections (Lincy et al. 2011; Marin et al. 2012; Moretti 2017); however, mycotoxin characterization in F. lacertarum has not been characterized. To our knowledge, this is the first report of F. lacertarum causing disease to sorghum in North Carolina and the United States. Fusarium lacertarum may cause impactful losses to sorghum producers due to direct yield and quality losses by the pathogen as well as the potential for mycotoxins to impact trade.

Fusarium Species from Sorghum in Thailand

Sorghum is the fifth most important cereal worldwide, spreading from Africa throughout the world. It is particularly important in the semi-arid tropics due to its drought tolerance, and when cultivated in Southeast Asia commonly occurs as a second crop during the dry season. We recovered Fusarium from sorghum in Thailand and found F. proliferatum, F. thapsinum and F. verticillioides most frequently, and intermittent isolates of F. sacchari and F. beomiforme. The relatively high frequencies of F. proliferatum and F. verticillioides, suggest mycotoxin contamination, particularly fumonisins and moniliformin, should be evaluated. Genetic variation within the three commonly recovered species was characterized with vegetative compatibility, mating type, Amplified Fragment Length Polymorphisms (AFLPs), and female fertility. Effective population number (N e ) was highest for F. verticillioides and lowest for F. thapsinum with values based on mating type allele frequencies higher than those based on female fertility. Based on AFLP genetic variation, the F. thapsinum populations were the most closely related, the F. verticillioides populations were the most distantly related, and the F. proliferatum populations were in an intermediate position. The genetic variation observed could result if F. thapsinum is introduced primarily with seed, while F. proliferatum and F. verticillioides could arrive with seed or be carried over from previous crops, e.g., rice or maize, which sorghum is following. Confirmation of species transmission patterns is needed to understand the agricultural systems in which sorghum is grown in Southeast Asia, which are quite different from the systems found in Africa, Australia, India and the Americas.

Amylose-Free ("waxy") Wheat Colonization by Fusarium spp. and Response to Fusarium Head Blight

Hexaploid waxy wheat (Triticum aestivum L.) has null mutations in Wx genes and grain lacking amylose with increased digestibility and usability for specialty foods. The waxy cultivar Mattern is susceptible to Fusarium head blight (FHB) caused by Fusarium graminearum species complex, which produces the mycotoxin deoxynivalenol (DON). In experiment 1, conducted during low natural FHB, grain from waxy breeding lines, Mattern, and wild-type breeding lines and cultivars were assessed for Fusarium infection and DON concentration. Nine Fusarium species and species complexes were detected from internally infected (disinfested) grain; F. graminearum infections were not different between waxy and wild-type. Surface- and internally infected grain (nondisinfested) had greater numbers of Fusarium isolates across waxy versus wild-type, but F. graminearum-like infections were similar; however, DON levels were higher in waxy. In experiment 2, conducted during a timely epidemic, disease severity, Fusarium-damaged kernels (FDK), and DON were assessed for waxy breeding lines, Mattern, and wild-type cultivars. Disease severity and FDK were not significantly different from wild-type, but DON was higher in waxy than wild-type lines. Across both experiments, waxy breeding lines, Plant Introductions 677876 and 677877, responded similarly to FHB as moderately resistant wild-type cultivar Overland, showing promise for breeding advanced waxy cultivars with reduced FHB susceptibility.

Differences in Fusarium Species in brown midrib Sorghum and in Air Populations in Production Fields

Several Fusarium spp. cause sorghum (Sorghum bicolor) grain mold, resulting in deterioration and mycotoxin production in the field and during storage. Fungal isolates from the air (2005 to 2006) and from leaves and grain from wild-type and brown midrib (bmr)-6 and bmr12 plants (2002 to 2003) were collected from two locations. Compared with the wild type, bmr plants have reduced lignin content, altered cell wall composition, and different levels of phenolic intermediates. Multilocus maximum-likelihood analysis identified two Fusarium thapsinum operational taxonomic units (OTU). One was identified at greater frequency in grain and leaves of bmr and wild-type plants but was infrequently detected in air. Nine F. graminearum OTU were identified: one was detected at low levels in grain and leaves while the rest were only detected in air. Wright's F statistic (F_ST) indicated that Fusarium air populations differentiated between locations during crop anthesis but did not differ during vegetative growth, grain development, and maturity. F_ST also indicated that Fusarium populations from wild-type grain were differentiated from those in bmr6 or bmr12 grain at one location but, at the second location, populations from wild-type and bmr6 grain were more similar. Thus, impairing monolignol biosynthesis substantially effected Fusarium populations but environment had a strong influence.

Influence of temperature, water activity and incubation time on fungal growth and production of ochratoxin A and zearalenone by toxigenic Aspergillus tubingensis and Fusarium incarnatum isolates in sorghum seeds

The major objective of this study was to describe the effect of water activity and temperature on radial growth and production of ochratoxin A (OTA) and zearalenone (ZEA) on sorghum grains of three Aspergillus tubingensis and three Fusarium incarnatum isolates. The water activity range was 0.91-0.99 a_w for F. incarnatum isolates and 0.88-0.99 a_w for A. tubingensis isolates. Temperatures of incubation were 15, 25 and 37°C for both species. Mycotoxin production was determined after 7, 14, 21 and 28days depending on the growth rate of the six isolates. Maximum growth rates (mm/day) were observed at 37°C and 0.99 a_w for A. tubingensis isolates and at 0.99 a_w and 25°C for F. incarnatum isolates. A. tubingensis was able to grow at 15°C only at the highest a_w levels (0.97 and 0.99 a_w). However, at this temperature F. incarnatum grew at 0.94 a_w. Optimum ochratoxin A production was observed at 0.97 a_w×37°C whereas optimal conditions for ZEA production varied from one isolate to another. Moreover, isolates of F. incarnatum from Tunisia do not require high a_w and temperature levels to yield maximum levels of ZEA. In general, our results showed that there is no correlation between the growth and production of ZEA in the case of F. incarnatum. This is the first study on the water activity and temperature effect on growth rate and ZEA production of F. incarnatum. Our results show that sorghum grains not only support growth but also OTA and ZEA production by A. tubingensis and F. incarnatum, respectively.

Effect of waxy (Low Amylose) on Fungal Infection of Sorghum Grain

Loss of function mutations in waxy, encoding granule bound starch synthase (GBSS) that synthesizes amylose, results in starch granules containing mostly amylopectin. Low amylose grain with altered starch properties has increased usability for feed, food, and grain-based ethanol. In sorghum, two classes of waxy (wx) alleles had been characterized for absence or presence of GBSS: wx(a) (GBSS(-)) and wx(b) (GBSS(+), with reduced activity). Field-grown grain of wild-type; waxy, GBSS(-); and waxy, GBSS(+) plant introduction accessions were screened for fungal infection. Overall, results showed that waxy grains were not more susceptible than wild-type. GBSS(-) and wild-type grain had similar infection levels. However, height was a factor with waxy, GBSS(+) lines: short accessions (wx(b) allele) were more susceptible than tall accessions (undescribed allele). In greenhouse experiments, grain from accessions and near-isogenic wx(a), wx(b), and wild-type lines were inoculated with Alternaria sp., Fusarium thapsinum, and Curvularia sorghina to analyze germination and seedling fitness. As a group, waxy lines were not more susceptible to these pathogens than wild-type, supporting field evaluations. After C. sorghina and F. thapsinum inoculations most waxy and wild-type lines had reduced emergence, survival, and seedling weights. These results are valuable for developing waxy hybrids with resistance to grain-infecting fungi.

Isolation and characterization of the grain mold fungi Cochliobolus and Alternaria spp. from sorghum using semiselective media and DNA sequence analyses

Mold diseases, caused by fungal complexes including Alternaria, Cochliobolus, and Fusarium species, limit sorghum grain production. Media were tested by plating Fusarium thapsinum, Alternaria sp., and Curvularia lunata, individually and competitively. Dichloran chloramphenicol rose bengal (DRBC) and modified V8 juice (ModV8) agars, found to be useful, were compared with commonly used agar media, dichloran chloramphenicol peptone (DCPA) and pentachloronitrobenzene (PCNB). Radial growth, starting with mycelia or single-conidia and hyphal tips, demonstrated an effect of media. For isolation of grain fungi, DRBC and ModV8 were similar or superior to DCPA and PCNB. When seedlings were inoculated with conidia of C. lunata, Alternaria sp., F. thapsinum, or mixtures, the percentage of root infection ranged from 28% to 77%. For mixed inoculations, shoot weights, lesion lengths, and percentage of root infections were similar to F. thapsinum inoculations; most colonies recovered from roots were F. thapsinum. For Alternaria grain isolates, 5 morphological types, including Alternaria alternata, were distinguished by colony morphologies and conidial dimensions. Sequence analysis using a portion of the endo-polygalacturonase gene was able to further distinguish isolates. Cochliobolus isolates were identified morphologically as C. lunata, Curvularia sorghina, and Bipolaris sorghicola. Multiple molecular genotypes were apparent from rRNA internal transcribed spacer region sequences from Cochliobolus grain isolates.