Tracheomycosis or coffee wilt has emerged as a major disease of robusta coffee in Uganda in the past 10 years. Coffee wilt historically has been associated with Fusarium xylarioides Steyaert (teleomorph Gibberella xylarioides Heim and Sacc.), a species that has been classified as a member of Fusarium section Lateritium. We investigated the molecular phylogenetics of fusarial coffee wilt isolates by generating partial DNA sequences from two protein coding regions, translation elongation factor 1-α and beta-tubulin, in 36 isolates previously identified as F. xylarioides and related fusaria from coffee and other woody hosts, as well as from 12 isolates associated with a current coffee wilt outbreak in Uganda. These isolates fell into two morphologically and phylogenetically distinct groups. The first group was found to represent previously unidentified members of the Gibberella fujikuroi species complex (GFC), a clade that replaces the artificial Fusarium section Liseola. This group of isolates fit the original description of F. xylarioides, thus connecting it to the GFC. The second group, which was diverse in its morphology and DNA sequences, comprised four distinct lineages related to Fusarium lateritium. Our finding of unrelated species associated with coffee wilt disease has important implications regarding its epidemiology, etiology and control.
A strain of Fusarium lateritium causing a unique disease, sweetpotato chlorotic leaf distortion, and producing microconidia borne on polyphialides is described. The polyphialides produced by this strain of F. lateritium are compared to those produced by F. proliferatum and F. subglutinans in section Liseola and F. scirpi in section Gibbosum. The polyphialides produced by the sweetpotato strain of F. lateritium most closely resemble those formed by F. scirpi in section Gibbosum.
Abstract Fungi were isolated from soybean cyst nematode (SCN, Heterodera glycines) eggs collected in China, and 253 fungal isolates were assayed for production of compounds active against SCN and root-knot nematode (RKN, Meloidogyne incognita). Fungal isolates were grown for 3 and 7 days in potato dextrose broth (PDB), the culture broths were sterile-filtered to remove fungal biomass, and the filtrates were placed into 24-well plates to test for effects on egg hatch and juvenile motility. Meloidogyne incognita egg hatch ranged from 2 to 121% of hatch in PDB controls and H. glycines hatch from 15 to 224%. Activities of filtrates harvested after 3 and 7 days were significantly correlated. Only four isolates produced filtrates that significantly inhibited juvenile motility of SCN, RKN or both nematodes. This study identified fungal isolates capable of producing compounds active against these nematodes, and demonstrated that there was a low correlation in activity against SCN and RKN. The active fungal isolates are candidates for studies on identification of potential nematicides.
Fusisporium solani was described as the causal agent of a dry rot of potato in Germany in the mid 19th century. As Fusarium solani, the species became known as a plurivorous plant pathogen, endophyte, decomposer, and opportunistic pathogen of humans and nutritional symbiont of insects. In parallel, it became evident that the morphologically defined species F. solani represents a phylogenetically and biologically complex group of often morphologically cryptic species that has come to be known in part as the F. solani species complex (FSSC), accommodating several formae speciales and mating populations/biological species. The FSSC currently includes more than 60 phylogenetic species. Several of these have been named, but the majority remains unnamed and the identity of F. solani sensu stricto is unclear. To promote further taxonomic developments in the FSSC, lectoand epitypification is proposed for Fusisporium solani. Although no type material for F. solani is known to exist, the species was abundantly illustrated in the protologue. Thus, a relevant illustration provided by von Martius is selected as the lectotype. The epitype selected here originates from a rotting potato collected in a field in Slovenia. This strain causes a dry rot of artificially inoculated potatoes. It groups in the heretofore unnamed phylogenetic species 5, which is nested within clade 3 of the FSSC (FSSC 5). Members of this phylogenetic species have a wide geographic distribution and include soil saprotrophs and plant and opportunistic human pathogens. This typification is consistent with the original description of Fusisporium solani and the concept of F. solani as a widely distributed soil inhabitant and pathogen.
Mycotoxin mixtures are associated with Shiga toxin-producing Escherichia coli (STEC) infections in mature cattle. STEC are considered commensal bacteria in mature cattle suggesting that mycotoxins provide a mechanism that converts this bacterium to an opportunistic pathogen. In this study, we assessed the mycotoxin content of hemorrhaged mucosa in dairy calves during natural disease outbreaks, compared the virulence genes of the STECs, evaluated the effect of the mucosal mycotoxins on STEC toxin expression and evaluated a Celmanax®/Dairyman’s Choice™ application to alleviate disease. As for human infections, the OI-122 encoded nleB gene was common to STEC genotypes eliciting serious disease. Low levels of aflatoxin (1–3 ppb) and fumonisin (50–350 ppb) were detected in the hemorrhaged mucosa. Growth of the STECs with the mycotoxins altered the secreted protein concentration with a corresponding increase in cytotoxicity. Changes in intracellular calcium indicated that the mycotoxins increased enterotoxin and pore-forming toxin activity. A prebiotic/probiotic application eliminated the morbidity and mortality losses associated with the STEC infections. Our study demonstrates: the same STEC disease complex exists for immature and mature cattle; the significance of the OI-122 pathogenicity island to virulence; the significance of mycotoxins to STEC toxin activity; and, finally, provides further evidence that prebiotic/probiotic applications alleviate STEC shedding and mycotoxin/STEC interactions that lead to disease.
In diagnostic surveys conducted in parts of Benin and Nigeria to determine the incidence of pre-harvest cassava root and stem rot during the dry season, Macrophomina phaseolina (Tassi) Goidanich constituted 14.2 and 18.7% of the total fungi (n = 201) associated with cassava root and stem rot from Benin and Nigeria (1). Pathogenicity of M. phaseolina on cassava was tested with cv. Agric. Inocula for pathogenicity tests were prepared by incubating 5-mm-diameter mycelial plugs for each of five isolates (Mp 1 to Mp 5, all collected from Benin) with 500 ml of autoclaved, sterilized, dehusked rice seed for 14 days at 30°C. Five 30-cm-long stem portions per isolate were cut from healthy cassava, surface disinfested in hot water (52°C, 5 min), and planted into 1-liter pots containing autoclaved, sterilized sand mixed with 10 ml of air-dried inoculum. Five plants per isolate similarly treated but not inoculated served as controls. Plants were watered once a week, and maintained in a greenhouse under natural light at 28 to 30°C. Lower leaves of inoculated plants gradually wilted, usually preceded by chlorosis, and brown to black lesions formed on the lower stem portions of some roots. Control plants remained asymptomatic. Plant height and percentage of leaf wilt (determined by counting the number of leaves wilted per plant and dividing by the total number of leaves per plant) were measured on a weekly basis for 8 weeks for each of the control and inoculated plants. At the end of 8 weeks, lesion length on the lower stem was measured. There were significant differences (P < 0.05) in length of the lesions and percentage of leaf wilt induced by the different isolates of M. phaseolina. Isolate Mp 1 induced the longest lesion (7.2 cm), followed by Mp 4 (4.1 cm), Mp 3 and Mp 5 (3.8 cm each), and Mp 2 (1.2 cm). Mp 4 induced the highest percentage of wilted leaves (53%), followed by Mp 1, Mp 3, and Mp 5 (30%), and Mp 2 (10%). All five M. phaseolina isolates (except Mp 3) reduced plant height, compared with control treatments. M. phaseolina was isolated from all infected plants, and the identification was independently confirmed by the International Mycological Institute, Surrey, UK. This is the first report of M. phaseolina causing pre-harvest cassava root rot in Benin and Nigeria. Reference: (1) W. Msikita et. al. Plant Dis. 81:1332, 1997.
Abstract Fumonisins were produced by strains of Fusarium moniliforme and F. proliferatum on a medium consisting of 500 g yellow corn kernels and 500 mL distilled water added to a 30.5 × 61 cm autoclavable polyethylene bag. The corn was inoculated by drawing a suspension from a lyophilized culture into a sterile 5 mL syringe fitted with a 19 gauge needle and injecting 1 mL through the side of each polyethylene culture bag. Bags of inoculated com were incubated in the dark at 20° to 22°C for 4 weeks. Seven to 8 days after inoculation, holes were punched near the tops of the bags to promote aeration. After a 4 week incubation, cultures were soaked in chloroform–acetone (50 + 50, v/v) in 4 L flasks overnight to kill fungus and to remove water. Next, the culture media was filtered through 2 mm nylon mesh screens and air dried from 24 to 48 h. Fumonisin concentrations were determined by liquid chromatography/o-phthalaldialdehyde fluorescence. Confirmation was by gas chromatography/mass spectrometry. We observed that the 3 most important factors in the production of fumonisins in bulk corn cultures were temperature control, moisture, and aeration. Extraction by acetonitrile–water (50 + 50, v/v) for 30 min produced the highest yields of fumonisins. Measurable concentrations were reduced by as much as 50% when culture material was heated at 50°C overnight. Fusarium moniliforme strains consistently produced fumonisin B1 as the major component, but some strains of F. proliferatum produced fumonisin B2 and/or fumonisin B3 at higher concentrations than fumonisin B1. Results were calculated on the basis of dried culture material.
A strain of Fusarium lateritium causing a unique disease, sweetpotato chlorotic leaf distortion, and producing microconidia borne on polyphialides is described. The polyphialides produced by this strain of F. lateritium are compared to those produced by F. proliferatum and F. subglutinans in section Liseola and F. scirpi in section Gibbosum. The polyphialides produced by the sweetpotato strain of F. lateritium most closely resemble those formed by F. scirpi in section Gibbosum.
