1. Mycotoxins 63 (1), 27-38 (2013)
www.jstage.jst.go.jp/browse/myco Occurrence, mycotoxins and
toxicity of Fusarium species from Abelmoschus esculentus and
Sesamum indicum seeds Chibundu N. EZEKIEL 1,* , Cyril C.
NWANGBURUKA 2 , Gibson O. CHIOMA 2 , Michael SULYOK 3 , Benedikt
WARTH 3 , Clement G. AFOLABI 4 , Adenike A. OSIBERU 1 , Michael O.
OLADIMEJI 1 , Olarenwaju A. DENTON 2 , Grace O. TAYO 2 , Rudolf
KRSKA 3 1 Mycology/Mycotoxicology Research Unit, Department of
Biosciences and Biotechnology, Babcock University, Ilishan Remo,
Ogun State. Nigeria 2 Department of Agriculture and Industrial
Technology, Babcock University, Ilishan Remo, Ogun State. Nigeria 3
Center for Analytical Chemistry, Department of Agrobiotechnology
(IFA-Tulln), University of Natural Resources and Life Sciences
Vienna, Konrad Lorenzstr. 20, A-3430 Tulln, Austria 4 Department of
Crop Protection, Federal University of Agriculture, Abeokuta, Ogun
State, Nigeria Keywords: equisetin; fumonisins; Fusarium;
moniliformin; mycotoxins; okra; sesame; zearalenone (Received
September 30, 2012; Accepted February 8, 2013) Abstract Seeds of
two okra accessions and 17 samples of sesame seeds were examined
for contamination by Fusarium species. Altogether, 37 Fusarium
isolates were obtained from the two crops: 6 isolates from two okra
accessions and 31 isolates from 10 sesame samples. The isolates
belonged to three species: F. oxysporum, F. semitectum and F.
verti- cillioides. All isolates from okra were identified as F.
semitectum while the three species of Fusarium occurred in sesame.
Six randomly selected isolates from the two crops were screened for
their ability to produce mycotoxins in ofada rice culture and the
crude extracts of the mycotoxins were tested on week-old Clarias
gariepinus fingerlings. Six metabolites were produced by the
isolates in ofada rice: equisetin (EQUS), fumonisin B1 (FB1), FB2,
methyl-equisetin (M-EQUS), moniliformin (MON) and zearalenone
(ZEA). All isolates produced EQUS at concentrations ranging
454-29,983 g/kg. All isolates except F. semitectum BUFC 041 and F.
oxysporum BUFC 024 produced MON and ZEA, while three F. semitectum
isolates produced M-EQUS. Only F. verticillioides isolates produced
fumonisins. There was evidence of variation within species obtained
from both crops based on toxin profile and level of toxin produced.
The culture extracts of all isolates induced 100% lethality to C.
gariepinus fingerlings except for extracts of F. semitectum BUFC
041 which killed only 62.2% of the fingerlings, possibly due to the
absence of MON. Our data suggest that okra and sesame may be
potential sources of toxigenic Fusarium. Introduction Okra
(Abelmoschus esculentus), a major tropical vegetable, is directly
sown and exported outside its cultivation region after harvest. The
annual global production of okra fruit is estimated at 6,000,000
tonnes, Research Paper 27 Corresponding Author
Mycology/Mycotoxicology Research Unit, Department of Biosciences
and Biotechnology, Babcock University, Ilishan Remo, Ogun State.
Nigeria. Tel.: 234-7038167130. E-mail: [email protected] A full
color PDF reprint of this article is available at the journal WEB
site.
2. and countries in West and Central Africa and the Middle East
are noted to contribute a high quota to okra production and
consumption1, 2) . In particular, Nigeria ranks second to India as
the highest producers of okra globally2) . Okra is edible in
different forms which include the leaves, fruit and seeds. The
fruit serves as soup thickeners while the seeds could be dried as a
nutritious material for vegetable curds, or roasted and ground for
use as coffee additive or substitute3, 4) . Okra contains
carbohydrate, proteins and vitamin C in large quantities5) . The
amino acids in okra fruits and oil (60-70% unsaturated fatty acids)
contained in the seeds are comparable to amino acids and oils in
soybean. The oil has potential to reduce cholesterol in the human
body while the seed flour could be used to fortify cereal flour1) .
It is assumed that the numerous benefits derived from okra may be
threatened due to Fusarium attack on this crop which has been
observed in agricultural fields in Nigeria; this has recently led
researchers to investigate this observation. Consequently, there
are few data on fungal contamination of okra and among the few
available reports in Nigeria6, 7) ; none considered the
toxigenicity of Fusarium species though Fusarium species were found
to be the most predominant species in okra seeds. Sesame (Sesame
indicum L.) is an oil rich seed grown in many parts of the world
especially within the dry tropics between latitudes of 40 N and S.
In 2007, Nigeria ranked among the five largest producers of sesame;
producing seeds for oil which is used in local and international
delicacies as well as livestock feed2, 8) . Sesame is exported
outside Nigeria due to its oil-rich quality. Nutritionally, sesame
is also rich in amino acids, vitamins and other essential
nutrients; this makes the crop susceptible to colonization by
microorganisms especially fungi. During colonization, the fungi
utilize the nutrients in the seeds and this leads to seed deterio-
ration. In the process, toxic substances known as mycotoxins may be
produced9) . For example, up to 28 mycotoxins and other less
important fungal metabolites have been detected in sesame seeds in
Nigeria10) . The examples of fungal species that have been reported
to attack sesame especially on field causing huge yield losses
include Cercospora sesame, Fusarium spp., Pythium spp. and
Sclerotium spp9, 11, 12, 13) . However, no report is available on
the toxigenicity of Fusarium spp. in sesame in Nigeria. Mycotoxins
produced by Fusarium species include: butenolide, equisetin (EQUS),
enniatins, fusarins, beauvericin, fumonisins, fusaproliferin,
moniliformin (MON), trichothecenes and zearalenone
derivatives14,15) . These toxins occur as important contaminants,
both alone and in mixture, in food and feed. Several studies have
been carried out on Fusarium toxins to assess their toxicity using
brine shrimps or catfish finger- lings16, 17, 18, 19) . However,
there is limited information on the occurrence and toxigenicity of
Fusarium spp. and Fusarium toxins that invade and colonize okra
globally and to a lesser extent, sesame in Nigeria. Since both
crops are widely consumed in Nigeria and there is the constant need
to assess the mycotoxicological risk associated with such regularly
utilized crops by determining the diversity and toxigenicity
profile of isolates obtained from these crops, we embarked on this
study. Knowledge of the toxigenic fungal profile in these crops may
be useful in searching for better avenues towards the reduction of
pre-harvest and post-harvest spoilage which tend to threaten food
safety especially in tropical countries. Therefore, this research
aimed at determining the presence of Fusarium in okra and sesame
seeds, evaluating the isolates for their potential to produce
mycotoxins in rice culture and testing the culture extracts of the
isolates for toxicity to Clarias garie- pinus fingerlings.
28EZEKIEL et al. Mycotoxins
3. Materials and Methods SamplesSeeds (500 g each) of two okra
accessions (BAB 002 and BAB 003) were obtained from the germplasm
of the Department of Agriculture and Industrial Technology, Babcock
University, Nigeria, while 17 bulk samples (1.8-2 kg each) of
sesame seeds were collected from four markets in Plateau State,
Nigeria as described by Ezekiel et al10 ) . Both crops were
collected between April and May 2011. The markets are situated in
B/Ladi, Bokkos, Mekera and Vwang. About 125 g representative of
each sesame sample was randomly obtained by quartering. The okra
and sesame samples were stored at 4 C to prevent further
accumulation of microbes until analysis. Isolation and
characterization of Fusarium species in the seedsSeed belonging to
the two crops (A. esculentus and S. indicum) were surface
sterilized for 30 s in separate vials containing 2 % NaOCl. The
sterilized seeds were rinsed twice with distilled water and blotted
dry in between two folds of sterile Whatman #1 filter paper. Five
seeds of each crop were plated per Petri dish of
peptone-pentachloronitrobenzene agar (PPA), a semi selective medium
for Fusarium20) . Triplicates of each PPA plate per crop were set
up. Inocu- lated plates were incubated for 5 days under fluorescent
lights on a 12 h day/ night schedule at 22-24 C. Fusarium species
were transferred to a fresh PPA and incubated for 7 days under the
same condition. A single spore of each isolate was manipulated, and
incubated overnight on a water agar plate at 22-24 C. After
germination, the fungus was maintained on a modified Czapek Dox
complete medium (CM) and stored at 4 C until identification.
Identification of Fusarium isolates was performed based on
morphological characteristics using carnation leaf agar (CLA for
examination of sporodochia and uniform macro conidia under the
Olympus BX51 Digital Microscopy, Olympus Optical Co., LTD, Japan)
and potato dextrose agar (PDA, for evaluation of pigmentation and
colony morphology). Fusarium species were identified according to
the taxonomic criterion of Leslie and Summerell21) . Fusarium
verticillioides ATCC MYA 836 strain22) was used as reference for
the identification. Fusarium isolates identified were cultured on
CM slants in a 4 ml vial, and stored at 4 C. In vitro toxin
production by Fusarium species on ofada riceAbout 5 kg of uncooked
ofada rice (locally produced rice) was purchased from a fast-food
company in Ibadan, Nigeria. Six randomly selected Fusarium isolates
were grown on 100 g of autoclaved ofada rice in 500 ml Erlenmeyer
flask to determine the toxigenic potentials of each isolate. The
rice in each flask was inoculated with 2 ml of 1106 conidia per ml
of corre- sponding isolate after moisture equilibration to 45 %19)
. Duplicate flasks per isolate were inoculated. A control flask of
autoclaved ofada rice without inoculation was set up. The flasks
were incubated for 4 weeks at 25 C in the dark. Then, the rice was
dried in a hot air oven at 55 C until a constant dry weight was
achieved. The dried rice in each flask was ground using a Waring
blender. A 20 g portion of the rice powder was transferred to a 50
ml polypropylene tube and sent to the University of Natural
Resources and Life Sciences, Austria for multi-mycotoxin analysis.
The remaining rice powder samples were extracted with
acetonitrile/water/acetic acid (79 : 20 : 1, v/v/v)23, 24) . The
extracts obtained were used for the bioassay at Babcock University,
Nigeria. 29Vol. 63, No. 1, 27-38 (2013)
4. Analysis of Fusarium toxins on ofada riceAll analytical
samples were examined for Fusarium metabo- lites by LC-MS/MS
according to Sulyok et al 24 ) . and Vishwanath et al25) . The
analytical method has been extended to cover 320 metabolites,
transferred to a more sensitive mass spectrometer and pre-validated
for four matrices (Malachova et al., unpublished data). In brief, 5
g of sample was weighed into a 50 ml polypro- pylene tube
(Sarstedt, Germany) and extracted with 20 ml
acetonitrile/water/acetic acid (79 : 20 : 1, v/v/v) for 90 min on a
GFL 3017 rotary shaker (GFL, Burgwedel, Germany). Extracts were
diluted in a ratio of 11 in dilution solvent
(acetonitrile/water/acetic acid 20 : 79 : 1 , v/v/v) and directly
injected into the LC-MS/MS instrument. Chromatographic separation
was performed at 25 C on a Gemini C18-column, 1504.6 mm i.d., 5 m
particle size, equipped with a C18 43 mm i.d. security guard
cartridge (all from Phenomenex, CA, US) and coupled to an 1290
Series HPLC System (Agilent, Waldbronn, Germany). After an initial
time of 2 mins at 100 % eluent A, the proportion of eluent B was
increased linearly to 50 % within 2-5 mins and 100 % within 5-14
mins, followed by a holding-time of 4 mins at 100% eluent B and 2.5
mins column re-equilibration at 100 % eluent A pumped at a flow
rate of 1 ml/min. A QTrap 5500 LC-MS/MS System (Applied Biosystems,
CA, US) equipped with a TurboIonSpray electrospray ionization (ESI)
source was used to detect and quantify the fungal metabolites.
ESI-MS/MS was performed in the scheduled multiple reaction
monitoring (sMRM) mode both in positive and negative polarities in
two separate chromatographic runs per sample by scanning two
fragmentation reactions per analyte with the following settings:
source temperature 550 C; curtain gas 30 psi; ion source gas 1
(sheath gas) 80 psi, ion source gas 2 (drying gas) 80 psi, ion
spray voltage 4500 V and5500 V respectively, collision gas
(nitrogen) medium. The MRM detection windows were 54 and 96 secs in
the positive and negative ionization mode, respectively and the
cycle time was set to one sec. Mycotoxins were quantified by
external calibration (1/x weighted) using a multi-component
standard prepared from authentic standards and later adjusted for
apparent recoveries. For the determination of the apparent
recovery, sub-samples (0.25g each) of the control (autoclaved but
uninoculated rice) were spiked prior to extraction at one
concentration level and analyzed as described above. Limits of
detection (LOD) were estimated from calibration standards at low
concentration levels based on the signal-to-noise ratio (S/ N=3 :
1). Toxicity assay of Fusarium culture materialsThe lethal effects
of the Fusarium culture materials were determined using week-old
larvae of freshwater African catfish, C. gariepinus, otherwise
called fingerlings as previously illustrated by Ezekiel et al26) .
for aflatoxins and ochratoxin A. Clarias gariepinus was used
instead of brine shrimp (Artemia salina L.) larvae16) because it is
the commonly used species for bioassay in sub-Saharan Africa. In
addition, Gbore et al18) . determined the effect of fumonisin B1
(FB1) on hematological parameters of C. gariepinus. Briefly, 1000
actively motile fingerlings were purchased from the Fishery Section
of May-Flower School, Ikenne, Ogun State, Nigeria and maintained in
purified oxygen bags filled with freshwater. Prior to exposure and
before acclimatization, the fingerlings were sorted randomly into
groups of 45, which consisted of triplicate sub-groups of 15
fingerlings. The fingerlings in each group were exposed to the
fungal culture extracts after being acclimatized for 12h. The
extract concentrations tested on the fingerlings were 0.25g/ml,
0.5g/ml and 1 g/ml. The number of dead fingerlings per treatment
was recorded after 24 h and this was deter- mined by loss of
locomotion. Two controls were set up in same manner only that no
crude extract was added. 30EZEKIEL et al. Mycotoxins
5. Instead, the extraction solvent was added to a set of
control to determine if the lethality data obtained was due to the
toxins or extraction solvent. The other set received no treatment.
Data from this experiment were reported as means of triplicate
observations/concentrations. Data analysisAnalysis of all data was
performed using SPSS version 15.0. Mean and standard error of the
lethality data was calculated. Results and Discussion Fusarium
species are important plant pathogens that colonize crops on field
including grains, seeds and vegetables. This represents a high risk
of mycotoxicoses in pre-harvested or freshly harvested crops14 ) .
The seeds of the two okra accessions and 58.8 % (10 out of 17) of
sesame were contaminated with Fusarium species. A total of 37
Fusarium isolates were obtained from the okra (6 isolates) and
sesame samples (31 isolates), and they belonged to three species:
F. oxysporum, F. semitectum and F. verticillioides. All isolates
obtained in this study were characterized based on morphological
features and some distinguishing character- istics are given below.
Isolates of the three Fusarium species produced macroconidia of
different sizes. F. semitectum did not produce microconidia but
produced macroconidia with slightly curved and tapered apical cell
and foot shaped basal cell in contrast to macroconidia with curved
apical cell and notch or foot shaped basal cell that were produced
by Fusarium oxysporum and F. verticillioides. Fusarium oxysporum
and F. semitectum isolates produced smooth and rough chlamydospores
respectively, while F. verticillioides produced chains of
microconidia but no chlamydospores (Fig1). The characteristic
rabbit-ear macroconidia was also observed in all isolates of F.
semitectum. The pigmentation on PDA plates was brown and violet for
F. semitectum, and F. oxysporum and F. verticillioides. The
isolates obtained from okra were identified as F. semitectum while
the three species of Fusarium were obtained from sesame samples
(Table 1). F. semitectum had the highest occurrence (38.7 %) in the
sesame samples while F. verticillioides had the least occurrence
(25.8%). On the overall, F. semitectum repre- sented 48.6% of all
fusaria obtained from the two crops while F. oxysporum and F.
verticillioides represented 29.7% and 21.6 respectively. A wide
range of vegetables including okra, tomato, pepper and cucurbits
have been reported to harbor Fusarium species6, 27, 28, 29) .
Therefore, the recovery of isolates belonging to only F. semitectum
from okra seeds in this study is in line with those reports.
However, there may be a limitation in the use of only morphological
parameters for the characterization of the Fusarium isolates which
we obtained in this study; the possible reason previous studies6,
29) that detected Fusarium in okra considered the isolates as
Fusarium spp. Fusarium semitectum has been associated with bovine
pulmonary emphysema30) . On the other hand, not much has been
documented for Fusarium contamination in sesame. In this study,
three species were identified from nearly 60% of the sesame seeds;
this indicates the relative susceptibility of sesame seeds to
Fusarium contamination9, 11) . Data obtained from the LC-MS/MS
analysis of extracts of the six cultured Fusarium isolates showed
that six metabolites were produced on ofada rice grains (Fig. 2 and
Table 2). The six metabolites and their respective LODs and
recoveries (%) are given: EQUS (0.09, 108.1%), FB1 (6.01, 83.2%),
FB2 (6.09, 82.2%), methyl-equisetin (M-EQUS, 0.08, 100.5%), MON
(0.69, 115.3%) and zearalenone (ZEA, 0.19, 103.1%). Fusarium
semitectum isolates obtained from okra produced four of the
metabolites in the rice cultures (EQUS, 31Vol. 63, No. 1, 27-38
(2013)
6. Table 1.Incidence of Fusarium species in A. esculentus and
S. indicum seeds from Nigeria Seed Na Nb Nc Occurrence of Fusarium
species (%) F. semitectum F. oxysporum F. verticillioides Okra 2 2
6 6/6 (100.0) Sesame 17 10 31 12/31 ( 38.7) 11/31 (35.5) 8/31
(25.8) Total 19 12 37 18/37 ( 48.6) 11/37 (29.7) 8/37 (21.6) a
Number of samples analyzed. b Number of samples positive for the
presence of Fusarium species. b Number of isolates obtained. Fig.
1.Chlamydospore and conidial characters of F. semitectum (a and b),
F. oxysporum (c and d) and F. verticillioides (e and f) isolated
from A. esculentus and S. indicum seeds. a, b, d and e =
macroconidia; b = characteristic Rabbit-ear macroco- nidia of F.
semitectum; c = chlamydospore; f = characteristic chains of
microconidia of F. verticillioides. a b c d e f 32EZEKIEL et al.
Mycotoxins
7. Table 2.Toxin profile and toxicity of the culture extracts
of Fusarium species isolated from seeds of A. esculentus and S.
indicum in Nigeria Fusarium species and strains Source Toxin
profilea and concentration (g/kg) Mean SE Mortality (%)EQUS FB1 FB2
M-EQUS MON ZEA F. oxysporum BUFC 024 Sesame 911 0.5 100.00.00 F.
semitectum BUFC 067 Okra 452 0.5 0.3 100.00.00 BUFC 059 Okra 29,983
92 0.7 0.5 100.00.00 BUFC 031 Sesame 25,245 34 4.0 0.3 100.00.00
BUFC 041 Sesame 28,280 77 0.1 62.21.73 F. verticillioides BUFC 021
Sesame 2,147 20 2 1.7 0.3 100.00.00 Blankb 3 LOD LOD LOD LOD LOD a
EQUS = equisetin, FB1= fumonisin B1, FB2= fumonisin B2, M-EQUS=
methyl-equisetin, MON= moniliformin, ZEA = zeara- lenone. b
Un-inoculated rice incubated for 4 weeks. Fig. 2.Chromatograms of
six metabolites produced in ofada rice culture of Fusarium species.
AD, metabolites from F. semitectum BUFC 059; E and F, metabolites
from F. verticillioides BUFC 021. A = equisetin, B =
methylequisetin, C = moniliformin, D = zearalenone, E = fumonisin
B1, F = fumonisin B2. For better visibility, only the quantifier
ions are displayed. 33Vol. 63, No. 1, 27-38 (2013)
8. M-EQUS, MON and ZEA) while the six metabolites were produced
by the three Fusarium species isolated from sesame: F. oxysporum,
F. semitectum and F. verticillioides (Table 2 ). The ranges of the
metabolites produced by all Fusarium isolates were 452-29, Please
dose up the space in the figure/number (29,983 is correct and not
29,983) 983 g/kg (EQUS), 20 g/kg (FB1), 2 g/kg (FB2), 34 - 92 g/kg
(M-EQUS), 0.5-4 g/kg (MON) and 0.1-0.5 g/kg (ZEA). F. oxysporum is
the most widely dispersed of the Fusarium species and its strains
are generally viewed as non-toxigenic although they often can
synthesize various polyketide secondary metabolites with unknown
functions. Some strains of F. oxysporum have been reported to
produce fumonisins, MON, ZEA and other mycotoxins21) . The F.
oxysporum isolate (BUFC 024) obtained from sesame seeds in Plateau
State, produced only EQUS and MON. The absence of fumonisin
production by F. oxysporum (BUFC 024) affirms variation in strains
of F. oxysporum. F. semitectum is commonly found in the soil and
diverse aerial plant parts in tropical and sub-tropical areas. All
the F. semitectum isolates obtained from the two crops exhibited
similar morpho-characters on standardized media21 ) . However, the
two cultured isolates from each crop produced varying toxins and
concentration levels of the toxins on rice. F. semitectum is known
to produce apicidin, beauvericin, EQUS, fusapyrone, MON,
sambutoxin, trichothecenes and ZEA21, 31) . Only EQUS, M-EQUS, MON
and ZEA were produced by the four isolates of F. semitectum as
confirmed by the LC-MS/MS protocol used in this study. However, one
of the isolates from okra (BUFC 067) and sesame (BUFC 041) did not
produce M-EQUS and MON respectively. In addition, F. semitectum
BUFC 067 produced 98.5 % less EQUS than F. semitectum BUFC 059,
while F. semitectum BUFC 031 from sesame produced 10.7 % and 55.8 %
less EQUS and M-EQUS respectively, than F. semitectum BUFC 041.
These variations in type and concentration of metab- olite produced
by each set of the two tested F. semitectum isolates from the two
crops lead us to suggest that this study identified four F.
semitectum strains in okra and sesame. This corroborates previous
reports of Vogelgsang et al32) . that variation in Fusarium strains
as well as type of cereal substrate on which the strains are grown
may influence the type and levels of mycotoxin production by the
isolates. In the present report, each set of the two tested F.
semitectum isolates were obtained from the same crop/host and
location, and were grown on ofada rice from the same source and
incubated under similar conditions. Therefore, molecular studies on
the four isolates may be helpful in resolving the assumption since
the sole use of morphological features in characterizing Fusarium
species is a limitation of this study. This paper reports for the
first time M-EQUS production by F. semitectum in culture. Fusarium
verticillioides, previously referred to as F. moniliforme, produces
fumonisins21, 33) . Some strains are capable of producing very high
concentrations of this toxic metabolite while other strains
especially when grown on rice produce MON at trace level21) . The
findings from the present study showed that F. verticilli- oides
BUFC 021 obtained from sesame and grown on rice produced low
concentrations of fumonisins and traces of MON. This is in line
with the above reports. However, contrary to this report and that
of Nelson et al34 ) . is the fact that the F. verticillioides BUFC
021 isolate we obtained from sesame in Nigeria produced additional
mycotoxins (EQUS and ZEA) in rice as confirmed by LC-MS/MS. In
fact, Nelson et al. 34) discounted ZEA production by F.
verticillioides. This may then imply that some F. verticillioides
strains are capable of producing additional mycotoxins including
EQUS which was produced at a much higher concen- tration than
fumonisins. We recommend further investigation into this
observation, especially using strains obtained from diverse crops
and geographical locations including sub-tropical Africa. 34EZEKIEL
et al. Mycotoxins
9. The mean temperature (24.5-27.0 C) and pH (6.0-6.5) values
of the water used in raising the fingerlings were within the
recommended ranges for catfish production35) . At 24 hours, the
three concentrations of crude extracts from all the six isolates
that were tested showed 100% mortality towards the fingerlings
except for F. semitectum BUFC 041. The three concentrations (0.25
g/ml, 0.5 g/ml and 1 g/ml) of the culture extracts of F. semitectum
BUFC 041 killed 62.2%, 60.0% and 64.4% of the fingerlings
respectively (data not shown), with an overall mean percentage
mortality of 62.2% (28/45) (Table 2). The decrease in mortality of
fingerlings shown by extracts from F. semitectum BUFC 041 as
compared to extracts from other isolates may be due to the absence
of MON in the extract of F. semitectum BUFC 041. MON has been
previously reported to exert relatively high toxic effects in brine
shrimp larvae and day old quails in single administration17, 36) .
In addition, co-occurrence of mycotoxins is are known to influence
toxicity of the mycotoxins involved37) . Pedrosa and Borutova38)
also reported that the administration of two or more mycotoxins
could result in synergistic effects. The presence of MON in the
extracts of other isolates which showed 100% mortality may
therefore be justified for synergism. Furthermore, Sharma et al36)
. reported synergistic effects for FB1 and MON, stating that FB1
and MON had less toxicity when administered alone while their
combination was more toxic. This may be the reason for the 100%
lethality observed in extracts from F. verticillioides BUFC 021.
Gbore et al18) . also reported the toxic effects of FB1 to adult C.
gariepinus. Conclusion This paper has revealed the possible
contamination of okra and sesame by toxigenic Fusarium. This may
pose a threat to animals including birds that pick up the okra
seeds and humans who consume sesame and its products. The toxigenic
Fusarium in the okra seeds may also be transferred to the edible
fruits thus creating a higher risk situation for a wider range of
consumers. Good agricultural practices such as crop rotation, weed
control and post-harvest handling practices (e.g. sorting,
cleaning, proper drying and storage) should therefore be encouraged
to prevent the crops from contamination prior to harvesting and
thereafter39, 40) . Acknowledgements The permission to use
laboratory facilities and technical support received from
Pathology/Mycotoxin laboratory of the International Institute of
Tropical Agriculture, Nigeria is hereby acknowledged. Conict of
Interest Authors hereby declare no conflict of interest. References
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