ELNA J. VAN DER LINDE Mycology Unit PPRI, Private Bag X134, Pretoria, 0001 Several cases of bovine ergotism ascribed to the intake of fodder contaminated with yellow nut sedge ( Cyperus esculentus) ergotised by Claviceps cyperi
have been reported since 1996 from the eastern Highveld region in South
Africa. These were the first incidents of ergotism associated with a Claviceps species infecting a non-poaceous host. Claviceps cyperi
was described in 1967 from herbarium specimens collected between 1940
and 1944 in and around Pretoria in the former Transvaal Province, South
Africa, and has not been recorded elsewhere in the world. Besides the
above taxonomic account of C. cyperi and its apparent
noxiousness, no information is available on the fungus. This study was
undertaken to elucidate, in part at least, the symptomology and
epidemiology of the disease, and the pathology, toxicology and
phylogenetic relationship of C. cyperi.
Symptoms of ergot on nut sedge, germination of sclerotia of C. cyperi,
and the morphology of live specimens of the pathogen were described for
the first time. Honeydew associated with the disease is inconspicuous
and the initial symptom of infection was a black sooty layer on
inflorescences of infected plants due to colonisation of the honeydew
by the saprophytic fungus Cladosporium cladosporioides. Ergot
sclerotia started to develop in March and April and could be discerned
as small protuberances on inflorescences in the place of seed. Mature
sclerotia were purplish-black and required a resting period of about
two months before germinating. Germination occurred without prior cold
treatment, though exposure of the sclerotia to 5 C for 21 days
significantly increased the germination rate. Dimensions of sclerotia,
stipes, capitula, asci and ascospores of live specimens were somewhat
larger than in the original description, but the general morphology
supported treatment of C. cyperi as a distinct species. Comparison of C. cyperi with 15 other Claviceps
species available in the GenBank sequence database by means of
multilocus PCR fingerprinting of genomic DNA and sequence analysis of
the ITS1-5.8 rDNA-ITS2 and ß-tubulin gene intron 3 regions confirmed
that it is a separate species, phylogenetically the closest related to Claviceps zizaniae, the ergot fungus of wild rice (Zizania spp.). The sphacelial state of C. cyperi
was isolated and grown in culture on various media at different
temperatures. Optimal growth occurred at 24 C, with no growth evident
at 5 C and 32 C. The anamorph conformed to the description of Sphacelia, but an enteroblastic mode of conidiogenesis could not be confirmed and placement of the species in Sphacelia is therefore nomen provisorium.
Infection of yellow nut sedge by C. cyperi
could not be achieved in the greenhouse. Microscopic examination of
material collected in the field indicated that infection by C. cyperi,
unlike most other ergot species, not necessarily mimics the pollination
process, as infection of ovaries in some florets seemed to have already
occurred when stylodia only started protruding. The dark layer of the
omnipresent C. cladosporioides covering the honeydew appeared
to cause a physical barrier preventing florets from opening, hence
impeding development of sclerotia. Fusarium heterosporum was
also often present in the honeydew but did not seem to have any effect
on disease development. Large numbers of spotted maize beetle (Astylus atromaculatus)
were commonly observed visiting nut sedge inflorescences, whereas
larvae of an unidentified thrips species invaded and consumed the
ovaries and anthers. These insects possibly contributed to the
dissemination and/or natural control of the disease.
The main ergopeptine alkaloid in sclerotia of C. cyperi
was identified by HPLC and tandem mass spectroscopy as -ergocryptine,
with small amounts of ergosine, ergocornine and ergocrystine also
present. This alkaloid profile corresponds with the alkaloid content of
the fodder implicated in the outbreaks of bovine ergotism and is
typically associated with "summer syndrome" symptoms observed in
affected cattle. Although -ergocryptine is toxic to humans and
animals, its brominated derivative, 2-bromo--ergocryptine, is a
valuable drug with various pharmaceutical applications. Unfortunately,
all attempts at inducing C. cyperi to synthesise -ergocryptine in culture for commercial use have failed.
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