A review on mycotoxins and mycotoxicoses in ruminants and Equidae in South America

Of the mycotoxicoses caused by molds contaminating grains or their byproducts, leukoencephalomalacia of horses and less frequently aflatoxicosis in cattle have been reported in South America. However, the most important group of mycotoxins in the region are those caused by fungi that infect forages and other types of plants and have regional distribution. In this group, ergotism is important, both caused by Claviceps purpurea infecting grains or by Epichloë coenophiala infecting Schedonorus arundinaceus. Other important mycotoxicoses are those caused by indole-diterpenes produced by Clavicipitaceous fungi including Claviceps paspali in Paspalum spp., Claviceps cynodontes in Cynodon dactylon, and by Periglandula a seed transmitted symbiont associated with the tremorgenic plant Ipomoea asarifolia. The latter is an important poisoning in the northeastern and northern Brazil. Other important mycotoxicoses are those caused by swainsonine containing plants. It was demonstrated that swainsonine contained in Ipomoea carnea var. fistulosa is produced by an epibiotic fungus of the order Chaetothyriales whose mycelia develop on the adaxial surface of the leaves. Swainsonine is also produced by the symbiotic, endobiotic fungi Alternaria section Undifilum spp., which is associated with Astragalus spp. in the Argentinian Patagonia causing poisoning. Another form of mycotoxicosis occurs in poisoning by Baccharis spp., mainly B. coridifolia, a very important toxic plant in South America that contains macrocyclic trichothecenes probably produced by an endophytic fungus that has not yet been identified. Pithomycotoxicosis caused by Pithomyces chartarum used to be an important mycotoxicosis in the region, mainly in cattle grazing improved pastures of legumes and grasses. Slaframine poisoning, diplodiosis and poisoning by barley contaminated by Aspergillus clavatus has been rarely diagnosed in Brazil, Uruguay and Argentina.

Pest categorisation of Stenocarpella maydis

The EFSA Plant Health Panel performed a pest categorisation of Stenocarpella maydis, a clearly defined fungus causing seedling blight, stalk and ear rot in maize, its only confirmed main host. The pathogen occurs in many countries of North, Central and South America, Africa, Asia and Oceania where maize is grown commercially. It is present in the EU with restricted distribution (Czech Republic and Spain). Stenocarpella maydis is not included in Commission Implementing Regulation (EU) 2019/2072. Plants for planting (maize seeds) is the main pathway of entry and spread in the EU. Host availability and climate are favourable for the establishment of the pathogen in maize-growing areas of the EU. The pathogen has a direct impact on yield and quality of maize production. Phytosanitary measures are available to mitigate further introduction and spread of the pathogen into the EU. The Panel concludes that S. maydis satisfies all the criteria to be regarded as a potential Union quarantine pest.

Failure of diplodiatoxin to induce diplodiosis in juvenile goats

Diplodiosis is an important neuromycotoxicosis of ruminants in South Africa when grazing on harvested maize fields in winter. It is believed to be caused by mycotoxin(s) synthesised by Stenocarpella (Diplodia) maydis. Although several metabolites have been isolated from S. maydis culture material, none of these have been administered to ruminants to reproduce the disease. The objectives of this study were to isolate diplodiatoxin and to administer it to juvenile goats. Diplodiatoxin, considered as a major metabolite, was purified from S. maydis-infected maize cultures (Coligny 2007 isolate). Following intravenous administration of 2 mg and 4 mg diplodiatoxin/kg body weight for five consecutive days to two juvenile goats, no clinical signs reminiscent of diplodiosis were observed. Based on previous experimental results and if diplodiatoxin was the causative compound, the dosage regimen employed was seemingly appropriate to induce diplodiosis. In addition, intraruminal administration of 2 mg/kg diplodiatoxin to one goat for three consecutive days also did not induce clinical signs. It appears as if diplodiatoxin alone is not the causative compound. Other metabolites and/or mixtures of diplodiatoxin and other mycotoxins, when available in sufficient quantities, should also be evaluated.

Spongy Myelinopathy in Newborn Beef Calves Associated with Consumption of Corn Infected with Stenocarpella maydis

Stillbirth and perinatal mortality with neurological signs and lesions were diagnosed in two calves following ingestion by their dams of corn infected with Stenocarpella maydis during the third trimester of gestation. Grossly, the brain and spinal cord were unremarkable. Microscopically, diffuse severe status spongiosis of the white matter was detected in the cerebral hemispheres, brainstem, spinal cord and cerebellum. To the best of our knowledge this is the first pathological description of congenital disease in calves associated with the consumption of S. maydis-infected corn; the findings resemble those reported for the naturally occurring and experimentally induced disease in lambs.

Fungal Pathogens of Maize Gaining Free Passage Along the Silk Road

Silks are the long threads at the tips of maize ears onto which pollen land and sperm nuclei travel long distances to fertilize egg cells, giving rise to embryos and seeds; however fungal pathogens also use this route to invade developing grain, causing damaging ear rots with dangerous mycotoxins. This review highlights the importance of silks as the direct highways by which globally important fungal pathogens enter maize kernels. First, the most important silk-entering fungal pathogens in maize are reviewed, including Fusarium graminearum, Fusarium verticillioides, and Aspergillus flavus, and their mycotoxins. Next, we compare the different modes used by each fungal pathogen to invade the silks, including susceptible time intervals and the effects of pollination. Innate silk defences and current strategies to protect silks from ear rot pathogens are reviewed, and future protective strategies and silk-based research are proposed. There is a particular gap in knowledge of how to improve silk health and defences around the time of pollination, and a need for protective silk sprays or other technologies. It is hoped that this review will stimulate innovations in breeding, inputs, and techniques to help growers protect silks, which are expected to become more vulnerable to pathogens due to climate change.

Multi-mycotoxin screening of feed and feed raw materials from Africa

As animal feed is prone to infestation with mycotoxin-producing fungi, mycotoxin contamination of feed should be monitored. Here, we report a multi-mycotoxin survey of feed samples from Africa. We determined the concentrations of aflatoxins, fumonisins, deoxynivalenol, T-2 toxin, zearalenone and ochratoxin A in 1,045 samples of finished feed and feed raw materials (maize, maize silage, other cereals, etc.) from South Africa and 318 samples from Algeria, Tunisia, Morocco, Senegal, Côte d’Ivoire, Nigeria, Ghana, Namibia, Uganda, Kenya, Tanzania, Zambia and Madagascar. We compared the measured mycotoxin concentrations to regulatory limits or guidance values that are in effect in the European Union and analysed the co-occurrence of these mycotoxins. To determine the occurrence of other fungal secondary metabolites, a subset of the samples was analysed using a multi-analyte liquid chromatography tandem mass spectrometry-based method for the simultaneous detection of over 700 fungal metabolites. We found that 33.3% of maize samples and 54.4% of finished feed samples from Senegal, Côte d’Ivoire, Nigeria, Ghana, Namibia, Uganda, Kenya and Tanzania exceeded the European regulatory limit of 20 ng/g aflatoxins. The Fusarium mycotoxins zearalenone, fumonisins and deoxynivalenol were prevalent in all commodities from all countries, but concentrations were in most cases below European guidance values. Concentrations of deoxynivalenol and zearalenone were correlated. Several other Fusarium metabolites occurred frequently (e.g. moniliformin, beauvericin, aurofusarin) or in high concentrations (e.g. aurofusarin, fusaproliferin). Furthermore, high levels of diplodiatoxin were occasionally detected in samples from South Africa and the Alternaria metabolite tenuazonic acid was prevalent and reached high concentrations. In conclusion, aflatoxins frequently occurred in African feed samples in potentially unsafe concentrations. While Fusarium mycotoxins mostly occurred in concentrations below European guidance values, a correlation between deoxynivalenol and zearalenone concentrations suggests that toxicological interactions of these compounds deserve attention. Several less investigated fungal secondary metabolites occurred frequently or reached high concentrations.

Genetic Diversity of Stenocarpella maydis in the Major Corn Production Areas of the United States

The fungus Stenocarpella maydis (Berk.) B. Sutton, causal agent of Diplodia ear rot, is a prevalent corn (Zea mays L.) pathogen in the United States. Although S. maydis reduces grain quality, causes yield loss, and can produce mycotoxins in some countries, few studies have examined its biology and genetic diversity. We analyzed the genetic diversity of 174 S. maydis isolates sampled across the major corn production areas in the United States using nine different microsatellites. In all, 55 unique multilocus genotypes (MLG) were observed out of the 174 S. maydis isolates tested. After conducting a Bayesian clustering analysis by STRUCTURE, it was observed that the most probable number of genetic groups was two; however, no separation by their geographical location was identified. According to the minimum spanning network, the S. maydis population is linked across geographic regions of the United States but also contains private genotypes. Temporal diversity in the inoculum source was also observed at one location across 4 years. The haploid stage of S. maydis was confirmed and both mating type genes were amplified among selected isolates with unique MLG. We theorize that, although S. maydis is primarily an asexual fungus, sporadic cryptic recombination may occur, which could contribute to the genetic diversity observed in this study.

Comparative genomics of maize ear rot pathogens reveals expansion of carbohydrate-active enzymes and secondary metabolism backbone genes in Stenocarpella maydis

Stenocarpella maydis is a plant pathogenic fungus that causes Diplodia ear rot, one of the most destructive diseases of maize. To date, little information is available regarding the molecular basis of pathogenesis in this organism, in part due to limited genomic resources. In this study, a 54.8 Mb draft genome assembly of S. maydis was obtained with Illumina and PacBio sequencing technologies, and analyzed. Comparative genomic analyses with the predominant maize ear rot pathogens Aspergillus flavus, Fusarium verticillioides, and Fusarium graminearum revealed an expanded set of carbohydrate-active enzymes for cellulose and hemicellulose degradation in S. maydis. Analyses of predicted genes involved in starch degradation revealed six putative α-amylases, four extracellular and two intracellular, and two putative γ-amylases, one of which appears to have been acquired from bacteria via horizontal transfer. Additionally, 87 backbone genes involved in secondary metabolism were identified, which represents one of the largest known assemblages among Pezizomycotina species. Numerous secondary metabolite gene clusters were identified, including two clusters likely involved in the biosynthesis of diplodiatoxin and chaetoglobosins. The draft genome of S. maydis presented here will serve as a useful resource for molecular genetics, functional genomics, and analyses of population diversity in this organism.

Characterization of cell death caused by diplodiatoxin and dipmatol, toxic metabolites of Stenocarpella maydis

Diplodiosis, a neuromycotoxicosis of cattle and sheep grazing on mouldy cobs infected by Stenocarpella maydis, is considered the last major veterinary mycotoxicosis for which the causative mycotoxin is still unknown. The current study was aimed at characterizing the cell death observed in mouse neuroblastoma (Neuro-2a), Chinese hamster ovary (CHO-K1) and Madin-Darby bovine kidney (MDBK) cell lines exposed to the S. maydis metabolites (i.e. diplodiatoxin and dipmatol) by investigating the roles of necrosis and apoptosis. Necrosis was investigated using the lactate dehydrogenase (LDH) leakage and propidium iodide (PI) flow cytometry assays and apoptosis was evaluated using the caspase-3/7 and Annexin V flow cytometry assays. In addition, transmission electron microscopy (TEM) was used to correlate the cell death pathways observed in this study with their typical morphologies. Both diplodiatoxin and dipmatol (750 μM) induced necrosis and caspase-dependent apoptosis in Neuro-2a, CHO-K1 and MDBK cells. Ultrastructurally, the two mycotoxins induced mitochondrial damage, cytoplasmic vacuolation and nuclear fragmentation in the three cell lines. These findings have laid a foundation for future studies aimed at elucidating in detail the mechanism of action of the S. maydis metabolites.