|Jacobs-venter, Adriana - Agricultural Research Council Of South Africa|
|Geiser, David - Pennsylvania State University|
|Laraba, Imane - National Higher School Of Agronomy|
Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2018
Publication Date: N/A
Interpretive Summary: This study was conducted to characterize molds isolated from kikuyu grass associated with a putative mycotoxicosis of cattle in South Africa. This toxicosis is of considerable economic importance because the mortality rate in dairy cows suffering from kikuyu poisoning is high. Symptoms that precede death include gastrointestinal and neuromuscular distress. A putatively novel Fusarium species was isolated from kikuyu grass associated with an outbreak of kikuyu poisoning in 2010 and from plant debris in South African soil. Thus, the present study was initiated to use DNA sequence data from portions of several genes to determine the identity of the isolates recovered from kikuyu grass and to assess their relationship to several closely related species currently stored in the ARS Culture Collection (NRRL) that were received as F. anguioides, F. babinda, F. concolor, and F. polyphialidicum. Genetic analysis of the DNA sequence data indicated that the kiyuyu grass isolates represented a novel species that was formally described as F. austroafricanum. Because this species was implicated in the kikuyu poisoning outbreak, its toxin potential was assessed by analyses of whole-genome sequence data and by toxin analyses of cracked maize kernel cultures. Although analyses of the genome data suggested that F. austroafricanum possessed the genes required to produce at least four different toxins, none were detected in cultures of this mold on cracked corn kernel cultures. Future studies will be directed at determining whether these toxins are produced under different growth conditions. The results of this study should be of interest to toxicologists, veterinarians, and quarantine officials who are charged with developing robust strategies to improve food safety and agricultural biosecurity.
Technical Abstract: This study was conducted to characterize a novel Fusarium species isolated as an endophyte of kikuyu grass associated with a putative mycotoxicosis of cattle and from plant debris in soil in South Africa. Nested within the F. concolor species complex (FCOSC), it is described and illustrated here as F. austroafricanum sp. nov. Molecular phylogenetic analyses of multilocus DNA sequence data indicated it represents a genealogically exclusive lineage that is sister to F. concolor. Of the 109 isolates analyzed, only four were received correctly identified to species and these included 1/46 F. concolor, 1/31 F. babinda and 2/3 F. anguioides. The majority of the F. concolor and F. babinda isolates were received as F. polyphialidicum, which is a heterotypic synonym of the former species. Previously documented from South America, Africa, Europe and Australia, our data show F. concolor is also present in North America. The present study expands the known distribution of F. babinda in Australia to Asia, Europe and North America. Fusarium austroafricanum is most similar morphologically to F. concolor and F. babinda but differs from the latter two species in producing: (i) much longer macroconidia in which the apical cell is blunt to slightly papillate and the basal cell is only slightly notched, (ii) macroconidia via microcycle conidiation on water agar, and (iii) head blight disease symptoms in inoculated spikelets of the susceptible wheat cultivar Norm. BLASTn searches of the whole-genome sequence of F. austroafricanum NRRL 53441 and NRRL 66741, and related species in the FCOSC and F. babinda, were conducted to predict mycotoxin potential, using genes known to be essential for the synthesis of several mycotoxins and biologically active metabolites as the queries. Based on the presence of intact beauvericin, enniatin, fusarubin and bostrycoidin biosynthetic gene clusters in F. austroafricanum, we analyzed cracked corn kernel cultures of this species via liquid chromomatography-mass spectrometry (LC-MS) but failed to detect these mycotoxins in vitro. Lastly, a PCR assay for MAT idiomorph revealed that F. concolor and F. babinda were segregating for mating type locally two continents, suggesting they may possess a heterothallic sexual reproductive mode. However, the limited number of F. austroafricanum (N =3) and F. anguioides (N =2) strains available for typing were all MAT1-1.