Identification, virulence factors
characterization, pathogenicity and
aggressiveness analysis of Fusarium spp.,
causing wheat head blight in Iran
Nima Khaledi, Parissa Taheri &
Mahrokh Falahati Rastegar
European Journal of Plant Pathology
Published in cooperation with the
European Foundation for Plant
Pathology
ISSN 0929-1873
Volume 147
Number 4
Eur J Plant Pathol (2017) 147:897-918
DOI 10.1007/s10658-016-1059-7
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Author's personal copy
Eur J Plant Pathol (2017) 147:897–918
DOI 10.1007/s10658-016-1059-7
Identification, virulence factors characterization,
pathogenicity and aggressiveness analysis of Fusarium
spp., causing wheat head blight in Iran
Nima Khaledi & Parissa Taheri &
Mahrokh Falahati Rastegar
Accepted: 27 September 2016 / Published online: 7 October 2016
# Koninklijke Nederlandse Planteziektenkundige Vereniging 2016
Abstract Fusarium head blight (FHB), mainly caused
by Fusarium graminearum species complex (FGSC) and
also by other species of this genus, is one of the most
destructive cereal diseases with high yield losses and
mycotoxin contamination worldwide. The aim of this
study was to identify Fusarium species, characterize their
virulence factors such as trichothecene genotypes and cell
wall degrading enzymes (CWDEs), and also investigate
virulence of the isolates obtained from wheat plants with
FHB symptoms in Golestan province of Iran. Among 41
isolates tested, 24 were F. graminearum sensu stricto
(s.s.), six were F. proliferatum, four were F. culmorum,
three isolates belonged to each of F. subglutinans and
F. meridionale species and one isolate of F. asiaticum was
identified. Among Fusarium isolates, the nivalenol (NIV)
genotype could be found more frequently, followed by 3acetyl deoxynivalenol (3-ADON) and 15-acetyl
deoxynivalenol (15-ADON) genotypes. Production of
trichothecenes in autoclaved rice cultures was analyzed
by gas chromatography (GC) and confirmed by GC–MS.
The mean levels of NIV, 3-ADON and 15-ADON produced by Fusarium spp. were 824, 665 and 622 μg kg−1,
respectively. All Fusarium isolates were capable of producing CWDEs, mainly cellulase and xylanase. Lipase
and pectinase activities appeared later and at less quantities. In overall, the isolates FH1 of F. graminearum and
FH8 of F. proliferatum showed the maximum activity of
N. Khaledi : P. Taheri (*) : M. Falahati Rastegar
Department of Plant Protection, Faculty of Agriculture, Ferdowsi
University of Mashhad, P.O.Box: 91775-1163, Mashhad, Iran
e-mail: p-taheri@um.ac.ir
CWDEs, which was correlated with high level of their
virulence and aggressiveness on wheat. On the other
hand, correlation was observed between the level and
type of trichothecene produced by each isolate and its
virulence on wheat. Virulence of trichothecene producing
isolates was higher than that of non-trichothecene producing isolates. Our results suggested that CWDEs and
trichothecenes, as virulence factors, have considerable
roles on virulence and aggressiveness of the pathogen.
This is the first report on the effect of trichothecenes and
CWDEs on virulence and aggressiveness of Fusarium
spp. associated with FHB disease in wheat growing
regions of Iran.
Keywords Fusarium spp . Head blight .
Trichothecenes . Cellwalldegradingenzymes . Virulence
Introduction
Wheat (Triticum aestivum L.) is one of the major
cereal crops and a major source of human food
worldwide. The genus Fusarium has a global distribution and many species in the genus are phytopathogenic fungi infecting a wide range of crop plants
including cereals such as wheat, maize, oat and barley (Boutigny et al. 2011). Fusarium contamination is
a major agricultural problem, which significantly reduce grain yield and quality. More importantly, many
species in the genus Fusarium produce mycotoxins
that inhibit protein synthesis and cause several health
problems in humans and animals (Pestka 2010).
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The FHB, also called ear blight or scab, is economically one of the most important fungal diseases
of wheat (Spanic et al. 2010). In recent years, the
crop losses in Iran due to FHB increased significantly (Haratian et al. 2008; Davari et al. 2013). The
causal agents of this destructive disease are several
Fusarium species, especially F. graminearum species complex (FGSC) and F. culmorum (Boutigny
et al. 2014; Jennings et al. 2004; Nicholson et al.
2007). However, the spectrum of Fusarium spp.
involved in the disease varies at a local or regional
level depending on weather conditions especially
during wheat anthesis (Oerke et al. 2010).
To date, 16 species have been identified and formally
described within the FGSC (Van der Lee et al. 2015).
During the infection process, Fusarium spp. are able to
produce different mycotoxins such as trichothecenes,
zearalenone and fumonisins. Among them, trichothecenes are considered to be the most important ones
(Kimura et al. 2007). Trichothecenes are a large group
of sesquiterpenoid fungal metabolites, which are demonstrated as virulence factors in wheat-Fusarium interactions (Proctor et al. 1995). Increased trichothecene
accumulation is associated with higher level of fungal
virulence (Gardiner et al. 2010).
Trichothecene biosynthetic gene (Tri) clusters have
been characterized in FGSC and F. sporotrichioides
(Proctor et al. 2009; Brown et al. 2002). In both species,
the cluster consists of 12 genes that are involved in the
biosynthesis, regulation or transport of trichothecenes.
These genes are: Tri 5 (encoding a terpene synthase); Tri
4, Tri 11 and Tri 13 (encoding cytochrome P450
monooxygenases); Tri 3 and TRI7 (encoding acetyl
transferases), Tri 8 (encoding an esterase), Tri 6 and
Tri 10 (proposed to be regulatory genes) and Tri 12
(encoding a transporter). They have been classified into
four types (A, B, C, and D) based on structural features
(Chaudhary et al. 2011). Among type B-trichothecenes,
deoxynivalenol (DON), NIV, and their acetylated derivatives 3-ADON, 15-ADON, and 4-acetylnivalenol (4ANIV, syn. fusarenone-X) are those having a significant
impact on human and animal health (Pasquali and
Migheli 2014).
Different trichothecenes have various toxicological
properties (Van der Lee et al. 2015). DON is associated
with feed refusal, vomiting and suppressed immune
functions in consumers, while NIV is more toxic to
humans and domestic animals compared to DON (Ryu
et al. 1988). Trichothecenes also are potent phytotoxins,
Eur J Plant Pathol (2017) 147:897–918
with DON being more phytotoxic than NIV (Desjardins
2006). Only a hydroxyl group at C-4 in NIV distinguishes it from DON. However, these chemotype differences may have important fitness consequences for
the fungus, as differences in the pattern of oxygenation
and acetylation can alter the bioactivity and toxicity of
trichothecenes (Alexander et al. 1998).
Three strain-specific profiles of trichothecene
chemotypes have been identified within the Btrichothecene lineage of Fusarium: (i) DON and 3acetyldeoxynivalenol (3-ADON chemotype); (ii) DON
and 15-acetyldeoxynivalenol (15-ADON chemotype);
or (iii) NIV, its acetylated derivatives and low levels of
DON (NIV chemotype) (Ward et al. 2002). On the other
hand, in some sources the DON chemotype may exists
which includes Fusarium species producing 3-ADON
and 15-ADON (Pasquali and Migheli 2014; Miller et al.
1991). Substantial geographic variation in Fusarium
spp. and trichothecene chemotype diversity have been
observed (Miller 2002; Nielsen et al. 2012; Ward et al.
2008; Yli-Mattila et al. 2009). All chemotypes may be
present in the same geographical location; however,
only one is predominant. In cereals infected with Fusarium, the DON chemotype was found worldwide but
presence of other chemotypes is restricted to geographically specific regions (Qiu and Shi 2014).
The 3-ADON chemotype is dominant in Russian Far
East (Yli-Mattila and Gagkaeva 2010), Norway (Aamot
et al. 2015), northern Japan (Suga et al. 2008), Canada
(Ward et al. 2008) and northern Europe and has recently
been spreading from Finland to the north west of Russia
(Talas et al. 2011; Yli-Mattila et al. 2009). While, the 15ADON chemotype is dominant in central and southern
Europe (Yli-Mattila et al. 2013), northern China (Ji et al.
2007; Zhang et al. 2007), south Africa (Boutigny et al.
2011), Brazil (Scoz et al. 2009), Argentina (Alvarez
et al. 2011; Reynoso et al. 2011), southern Russia (YliMattila et al. 2009) and the mid-west of USA (Gale et al.
2007). In Asia, NIV chemotype is the most commonly
found type of trichothecene (Gale et al. 2007; Zhang
et al. 2007). Chemotype occurrence seems to be temperature dependent, the 15-ADON chemotype occurs in
cooler regions of China, whereas the NIV chemotype
occurred in warmer regions (Zhang et al. 2007). There is
also evidence for shifts in trichothecene chemotypes of
Fusarium. In China, DON strains are displacing NIV
strains (Suga et al. 2008; Zhang et al. 2010). In North
America, where for many years 15-ADON was the most
prevalent chemotype found in wheat (Schmale et al.
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2012), a shift from 15-ADON to 3-ADON occurred in
the last decade. In Russian Far East a shift from 15ADON to 3-ADON chemotype has been found (YliMattila and Gagkaeva 2010). The 3-ADON chemotype
has been found to grow more quickly and to produce
more trichothecenes and conidia than the 15-ADON
chemotype (Ward et al. 2008). So far, little is known
about trichothecene chemotypes in different regions of
Iran. Among the Fusarium isolates, NIV, 3-ADON and
15-ADON chemotypes were detected from different
fields of Mazandaran and Golestan provinces in the
northern region of Iran (Haratian et al. 2008;
Malihipour et al. 2012), while 15-ADON was the only
chemotype detected among the isolates collected from
fields of Ardabil province in the north west of Iran
(Davari et al. 2013; Malihipour et al. 2012).
The knowledge of mechanisms involved in virulence
of Fusarium spp. on wheat is very limited till now.
Fungal pathogens belonging to the genus Fusarium
have no specialized structures for penetration into plant
cell and enters the host via natural openings (Pritsch
et al. 2000), or penetrates the epidermal cell walls directly with short infection-hyphae (Wanyoike et al.
2002). Fusarium spp. are able to penetrate and invade
a host with the help of secreted CWDEs. Production of
CWDEs also enables the pathogen to penetrate, grow
and infect through the plant tissue (Kikot et al. 2009a).
Various CWDEs such as cellulase, xylanase, pectinase
and lipase could be produced by F. graminearum during
infection of wheat spikes (Ortega et al. 2013).
On the other hand, once the infection is established,
mycotoxins are released and they interfere with the
metabolism, physiologic processes and structural integrity of the host cell (Wagacha and Muthomi 2007).
Trichothecenes are considered as virulence factors during plant infection (Pasquali and Migheli 2014). In
wheat, the mycotoxin appears to be necessary for fungal
passage from infected florets into the rachis from where
it can further colonize the head (Jansen et al. 2005).
Trichothecenes are also associated with the pathogen
aggressiveness (Bai et al. 2002; Foroud and Eudes
2009). These mycotoxins are inhibitors of the protein
translational apparatus (Pestka 2007) and have elicitorlike activity in stimulating plant defence and cell death
(Desmond et al. 2008; Nishiuchi et al. 2006). Studies on
a strain of F. graminearum with mutation in the Tri5
gene encoding a DON biosynthetic enzyme revealed
that F. graminearum strains unable to produce DON
was less aggressive in both wheat and barley (Boddu
899
et al. 2007; Langevin et al. 2004). So, it is suggested that
DON and other trichothecenes are involved in virulence
by enabling pathogen spread within a spike, but they are
not required for initial infection (Bai et al. 2002).
In wheat and barley, trichothecene accumulation is
associated with aggressiveness of the fungal pathogen
(Gardiner et al. 2010). Reduced aggressiveness of NIV
chemotype compared to DON chemotypes, may be due
to the lower phytotoxicity of NIVon wheat (Eudes et al.
1997). These findings indicate that fitness and aggressiveness of FHB pathogens change with different
chemotypes.
The main objectives of this study were to: (i) identify
and determine the frequencies of Fusarium spp. isolated
from wheat plants with FHB symptoms, (ii) investigate
trichothecene chemotypes, (iii) evaluate activities of
CWDEs such as cellulase, xylanase, pectinase and lipase which are involved in the infection process of FHB
pathogens on host plant, and (iv) characterize virulence
factors, pathogenicity and aggressiveness of Fusarium
spp. and identify possible correlation. So, we mainly
described variability of Fusarium spp. isolates associated with wheat head blight under various perspectives,
which are directly or indirectly correlated with
pathogenicity.
Materials and methods
Sample collection
Forty-one isolates of Fusarium spp. were collected from
different wheat grain samples of various wheat cultivars
with symptoms such as ear blight and bleached grains
on ears in several regions of Golestan province in Iran
during the 2014 growing season (Fig. 1).
Isolation and morphological identification of Fusarium
species
For isolation of Fusarium spp., the grains were surface
sterilized by immersion in 1 % sodium hypochlorite for
3 min, and then rinsed three times in sterile distilled
water. The sterilized samples were placed in water agar
as a general medium and a semi-selective medium for
Fusarium, i.e., peptone- pentachloronitrobenzene agar
(PPA), and incubated at 25 °C in a 12 h light/dark cycle
for 10 days. The resulting Fusarium colonies were
single-spored and transferred to potato dextrose agar
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Eur J Plant Pathol (2017) 147:897–918
Fig. 1 Geographic locations of Fusarium species isolates obtained from wheat-growing regions in the Golestan province of Iran. Sampling
was performed of gray areas. ● F. graminearum; ■ F. culmorum; ○ F. proliferatum; □ F. meridionale; ♦ F. subglutinans; × F. asiaticum
(PDA), carnation leaf agar (CLA) (Fisher et al. 1982)
and spezieller nährstoffarmer agar (SNA) plates for
morphological identification (Leslie and Summerell
2006). Fusarium species were identified on the basis
of macroscopic characteristics such as pigmentations
and growth rates on PDA plates, as well as their microscopic features including size of macroconidia, presence
of microconidia and chlamydospores in cultures grown
on SNA and CLA (Leslie and Summerell 2006).
available DNA extraction kit (Genomic DNA isolation
kit IV; DENA Zist Asia, Iran) according to the manufacturer’s instructions. DNA concentration was quantified with a NanoDrop spectrophotometer and the quality
was verified by 1 % agarose gel electrophoresis. The
DNA samples were diluted using sterilized distilled
water with final concentration of 50 ng μL−1 and stored
at −20 °C until use.
Isolation of fungal genomic DNA
Species identification and trichothecene genotype
determination by PCR
Mycelial plugs (0.5 cm2) were picked up from PDA
plates and transferred into bottles containing 100 ml
potato dextrose broth (PDB) medium in 250 mL Erlenmeyer flasks, then incubated at 25 °C for 10 days.
Mycelial mats were dried between sterile filter papers
and ground to a fine powder with liquid nitrogen. Total
genomic DNA was extracted with a commercially
To confirm the morphological identification of species,
conventional PCR was performed using specific primers
(Table 1) for molecular identification of seven Fusarium
species, which may potentially infect wheat kernels in
the investigated area. The PCR reaction was performed
in a 25 μl volume, each reaction contained 7.5 μL of
sterile water, 12.5 μL of PCR Master Mix (Pars Tous,
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Table 1 Primer sequences, product sizes and annealing temperatures used for PCR identification of Fusarium species
Species
Primer
Sequences (5′-3′)
Product size
(bp)
PCR conditions
(anneal/extend)
Reference
F. graminearum
Fg16F
Fg16R
CTCCGGATATGTTGCGTCAA
GGTAGGTATCCGACATGGCAA
400–500
60 °C/60s
Nicholson et al. (1998);
Castañares et al. (2014)
F. culmorum
OPT18F
OPT18R
GATGCCAGACCAAGACGAAG
GATGCCAGACGCACTAAGAT
472
59 °C/30s
Schilling et al. (1996);
Williams et al. (2002)
F. subglutinans
61-2 F
61-2R
GGCCACTCAAGCGGCGAAAG
GTCAGACCAGAGCAATGGGC
445
64 °C/60s
Möller et al. (1999)
F. proliferatum
PRO1-F
PRO1-R
CTTTCCGCCAAGTTTCTTC
TGTCAGTAACTCGACGTTGTTG
585
57 °C/50s
Iran), 1 μL of 10pM each forward and reverse primers
and 3 μL of template DNA. The PCR cycle consisted
of an initial denaturation step at 94 °C for 2 min
followed by 35 cycles of denaturation (95 °C for
35 s), annealing (times and temperatures for each
primer pair listed in Table 1), extension (72 °C for
30 s) and final extension at 72 °C for 7 min. All
primers used in this study were purchased from
Macrogen (South Korea).
For trichothecene genotypes identification, specific
primers for DON, NIV, 3-ADON and 15-ADON forms
were used (Table 2). Two multiplex PCR assays were
used to evaluate trichothecene genotypes in field populations of Fusarium. The DON and NIV genotypes were
identified using a multiplex PCR assay to amplify portions of the Tri5, Tri5-Tri6 intergenic, Tri7 and Tri13
genes (Doohan et al. 1999; Li et al. 2005; Waalwijk et al.
2003). The DON, 3-ADON, 15-ADON and NIV genotypes were identified using a multiplex PCR assay to
amplify portions of Tri3 and Tri12 (Ward et al. 2002).
PCR amplification of Tri5, Tri5-Tri6 intergenic, Tri7
and Tri13 genes were performed as previously described
(Doohan et al. 1999; Li et al. 2005; Waalwijk et al.
2003). The PCR amplification of Tri12 and Tri3
consisted of an initial step at 94 °C for 10 min, followed
by two cycles of 94 °C for 30 s, 59 °C for 30 s and 72 °C
for 30 s. The annealing temperature was stepped down
every two cycles to 58, 56, 54, 53, 52 and 51 °C, then
Table 2 Primer identification, sequences and expected amplicon sizes for trichothecene mycotoxin chemotypes of Fusarium
Primer
designation
Primer sequence
Target gene
3CON (R)
3NA (F)
TGGCAAAGACTGGTTCAC
GTGCACAGAATATACGAGC
Tri3
3D15A (F)
ACTGACCCAAGCTGCCATC
Amplicon
(bp)
Trichothecene
mycotoxin
chemotypes
840
NIV
610
15-ADON
Reference
Ward et al. (2002)
3D3A (F)
CGCATTGGCTAACACATG
243
3-ADON
TRI5 (F)
TRI5 (R)
AGCGACTACAGGCTTCCCTC
AAACCATCCAGTTCTCCATCT
Tri5
544
Trichothecene producers
Doohan et al. (1999)
ToxP1
ToxP2
GCCGTGGGGRTAAAAGTCAAA
TGACAAGTCCGGTCGCACTAGCA
Tri5-Tri6
intergenic
300
360
DON
NIV
Li et al. (2005)
MinusTri7F
MinusTri7R
TGGATGAATGACTTGAGTTGACA
AAAGCCTTCATTCACAGCC
Tri7
483
DON
Doohan et al. (1999)
Tri13F
Tri13R
TACGTGAAACATTGTTGGC
GGTGTCCCAGGATCTGCG
Tri13
234
415
DON
NIV
Waalwijk et al. (2003)
12CON (R)
12NF (F)
CATGAGCATGGTGATGTC
TCTCCTCGTTGTATCTGG
Tri12
840
NIV
12-15 F (F)
TACAGCGGTCGCAACTTC
670
15-ADON
12-3 F (F)
CTTTGGCAAGCCCGTGCA
410
3-ADON
Ward et al. (2002)
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50 °C for 21 cycles, with a final extension at 72 °C for
10 min (Schmale et al. 2011).
Mycotoxin analyses in laboratory cultures
Mycotoxin production of the Fusarium isolates in laboratory cultures was investigated according to Alvarez
et al. (2009). Briefly, 25 g of rice (Oryza sativa L.)
grains was soaked in 100 ml of sterile distilled water
for 6 h. Water was drained and the soaked rice was
autoclaved twice. Five milliliters inoculum suspension
of 1 × 105 conidia mL−1 from each isolate was added to
each flask and incubated at 26 ± 1 °C in darkness for
3 weeks. The rice-fungi mixtures were ground in a
mortar and then dispensed in an Erlenmeyer flask with
75 ml of acetonitrile: methanol: water (80:5:15, v/v).
Approximately 10 ml of the sample extract was gravity
filtered and 5 ml aliquot of the purified extract was
transferred into a vial. The solvent was evaporated at
55 °C for 1 h. The analysis was carried out using a fused
silica capillary DB-5 column (30 m × 0.25 mm i.d.; film
thickness 0.25 μm) for detection and quantification of
NIV, DON, 3-ADON and 15-ADON. Nitrogen was
both the carrier and auxiliary gas. The injection volume
was 1 μl and total running-time was 30 min for each
sample. Detection limits were 20 μg kg−1 for DON,
50 μg kg−1 for NIV, 3-ADON and 15-ADON. Mycotoxin production was confirmed using an Agilent
7890A gas chromatograph with mass spectroscopy,
which was performed under electron energy conditions
of 70 eV as described by Alvarez et al. (2009).
Enzymatic analyses
According to previous studies on the activity of
CWDEs in vitro, most enzyme activities are observed
within 10 days after inoculation (Kikot et al. 2009;
Ortega et al. 2013). Based on these observations,
pectinase and cellulase activity were evaluated in this
study within 10 days. The test for each enzyme had
three replicates for each isolate and the experiment
was repeated two times.
Pectinase assay
Cultures were performed in 500 mL Erlenmeyers with
250 mL culture medium as previously described
(MacMillan and Voughin 1964). Pectinase activity was
determined based on the amount of reducing sugar (D-
Eur J Plant Pathol (2017) 147:897–918
galacturonic acid) released in culture supernatant. The
amount of D-galacturonic acid was determined by
dinitrosalicylic acid colorimetric method of Colowich
(1995) and absorbance was measured at 540 nm. The
unit of enzyme activity was defined as the amount of
enzyme that released 1 μ mol of galacturonic acid per
minute according to the standard curve. The standard
curve was drawn based on the absorbance in different
concentrations (μg ml−1) of D-galacturonic acid.
Cellulase assay
Cultures were performed in 500 mL Erlenmeyers with
250 mL culture medium as described by Abdel-Razik
(1970). After inoculation, incubation was carried out
under shaking (150 rpm) at 27 °C and darkness for
10 days. Cellulase activity was investigated using the
method of Wood and Bhat (1988). The absorbance was
measured at 550 nm and the amount of reducing sugar
released was calculated from the standard curve of glucose. One unit of cellulase activity was defined as the
amount of enzyme that catalyzed 1.0 μ mol of glucose
per minute during the hydrolysis reaction.
Xylanase assay
Cultures were performed in 500 mL Erlenmeyers with
250 mL culture medium as described by Miller (1959).
Xylanase activity was investigated using the method of
Bailey et al. (1992). Absorbance was read at 540 nm and
the amount of reducing sugar released was calculated
from the standard curve of glucose. One unit of xylanase
activity was defined as the amount of enzyme that
liberates 1.0 μ mol of reducing sugars equivalent to
xylose per minute under the assay conditions described.
Lipase assay
Cultures were performed in 500 mL Erlenmeyers with
250 mL culture medium as described by Ortega et al.
(2013). Lipase activity was investigated using the method of Ortega et al. (2013). Lipase hydrolytic activity was
measured spectrophotometrically at 440 nm with pnitrophenyl palmitate (p-NPP, 1 mM in acetone) as
substrate at 37 °C in 50 mM Tris–HCl buffer (pH 7.0).
One unit of enzyme activity was defined as the amount
of enzyme that releases 1 μ mol of p-NPP per minute
under the above mentioned reaction conditions.
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Plant materials
Virulence analysis on wheat spikes
Spring wheat cultivar (cv.) Falat, which is susceptible to
FHB (Soltanloo et al. 2011) and obtained from Agricultural Research Center of Khorassan Razavi province in
Iran, was used for pathogenicity testes. The seeds were
surface sterilized with 1 % sodium hypochlorite for
1 min, rinsed three times with sterile distilled water
and incubated for 5 days on a wet sterile filter paper in
Petri dishes at 25 °C. Germinated seeds were each sown
in the 15 cm-diameter plastic pots filled with potting
soil, which had been autoclaved at 121 °C for a minimum of 30 min at 100 kPa (15 psi) on 2 successive days
and grown in greenhouse (30 ± 4 °C; 16/8 h light/dark
photoperiod). The soil used in this experiment, was a
combination of clay, sand and farmyard manure with the
ratio of 2:1:1 (v/v/v).
Virulence of all isolates on wheat spikes was evaluated
using the method described by Yoshida et al. (2007). At
the flowering stage (ZGS 64 to 65), 10 mL of spore
suspension (1 × 105 conidia mL −1) amended with
0.05 % Tween 20 was sprayed onto the spikes of each
plant. The inoculated plants were incubated overnight in
greenhouse at 18-25 °C, with 100 % humidity. Then, the
plants were placed in a plastic bag for 3 days to maintain
high relative humidity. Control plants were only treated
with sterile distilled water. Inoculated wheat heads were
evaluated after 10 days and the FHB disease severity
was estimated. Disease severity was measured as the
percentage of infected spikelet(s) within the spike using
a 0 to 5 scale (0 = no disease, 1 = to 20 %, 2 = to 40 %,
3 = to 60 %, 4 = to 80 % and 5 = more than 80 % disease
severity) (Wan et al. 1997) and the FHB index was
calculated as described previously (Amarasinghe et al.
2013). Each test had ten replicates arranged in a
completely randomized design, and the experiment
was repeated two times.
Inoculum preparation
Fungal inocula were produced in Mung Bean Broth
(MBB) medium using the method described by Zhang
et al. (2013). Conidial suspensions were diluted to a
final concentration of 1 × 105 conidia mL−1 containing
0.05 % (v/v) Tween 20.
Virulence analysis on seedlings
Virulence capability of all Fusarium isolates on seedlings was investigated using the method described by
Gargouri-Kammoun et al. (2009). At the two- to threeleaf stage (Zadoks’ growth stage (ZGS) 12 to 13), a
volume of 250 μl of a spore suspension (1 × 105 conidia
mL−1) was placed at the stem base and leaf primordial of
each plant. Plants used as controls were inoculated in a
similar manner with sterile distilled water. Plants were
incubated in the dark at constant 100 % relative humidity and 22 °C for 24 h, and twenty one days after
inoculation, each plant was carefully pulled out and
washed. Disease severity was graded into five classes
based on the proportion of stem discoloration (0 = no
discoloration; 1 = 1 to 25 %; 2 = 26 to 50 %; 3 = 51 to
75 %; 4 = more than 75 %; 5 = dead plant) as described
by Fernandez and Chen (2005) and the disease index
(DI) was calculated as described previously (Taheri and
Tarighi 2010). Each test had ten replicates arranged in a
completely randomized design, and the experiment was
repeated two times.
Detached-leaf assay
The wheat plants were grown in greenhouse with 12 h
photoperiod, RH of 75 %, and a day: night temperature
of 18 °C: 12 °C. After 14 days, 4 cm segments from the
mid-section of the first leaf were harvested, and placed
adaxial surface up on the surface of 0.5 % water agar as
described by Browne and Cooke (2004). Leaf segments
were inoculated at the center of the adaxial surface with
5 μl inoculum suspension of 1 × 105 conidia mL−1 containing 0.05 % (v/v) Tween 20. Sterile distilled water
was applied on the control leaves. Petri dishes were
incubated at 25 °C with a 12 h: 12 h light: dark cycle.
After 5 days, the length of necrotic lesions was measured. The test included four replicates for each isolate
and the experiment was repeated two times.
Assessment of aggressiveness
Aggressiveness of each isolate of Fusarium spp. on
seedlings, wheat spikes, and detached leaves were
carried out using the methods described by Malihipour
et al. (2012) and Pariaud et al. (2009). Analysis of
aggressiveness was done based on determining hours
post inoculation (hpi) for disease symptom appearance.
Author's personal copy
904
Aggressiveness of all isolates was checked after every
12 h.
Statistical analysis
All experiments were set up in a completely randomized
design. The data were analyzed by one-way analysis of
variance (ANOVA) and comparison of means was carried out using the Duncan’s Multiple Range Test at the
level of P ≤ 0.05. Statistical analysis was performed
with statistical package for the social sciences (SPSS;
version 22) software.
Results
Morphological identification of Fusarium isolates
Morphological observations showed that width of
macroconidia ranged from 4.0 to 7.0 μm for FGSC
(Fig. 2a), 4.0 to 4.6 μm for F. graminearum (Fig. 2b),
4.0 to 4.5 μm for F. asiaticum (Fig. 2c), 3.8 to 4.3 μm
Fig. 2 Morphological characters of Fusarium species.
macroconidium of FGSC (a), macroconidium of F. graminearum
(b), macroconidium of F. asiaticum (c), macroconidium of
F. meridionale (d), macroconidium of F. culmorum (e),
Eur J Plant Pathol (2017) 147:897–918
for F. meridionale (Fig. 2d), 5.0 to 6.0 μm for
F. culmorum (Fig. 2e). Based on morphological characters of conidia, chlamydospores and conidiophores, 41
Fusarium isolates were identified which belonged to
four species (Table 3, Fig. 2). The most common species
identified were FGSC (68.3 %) and F. proliferatum
(14.6 %). Less frequently isolated species included
F. culmorum (9.8 %) and F. subglutinans (7.3 %).
Molecular identification of Fusarium isolates using
species-specific PCR assay
The list of PCR primers used to identify Fusarium
species is presented in Table 1. The Fg16F/Fg16R
primers are not completely specific to F. graminearum
sensu stricto, but they gave products of different size
(400–500 bp), as described by Nicholson et al. (1998).
F. graminearum s.s. gave a product of about 400 bp,
while F. asiaticum gave a PCR product of about 550 bp
and F. meridionale gave a product of about 500 bp, as
described by Castañares et al. (2014). Molecular analysis using Fg16F/Fg16R primers revealed that from 28
macroconidium of F. proliferatum (f), macroconidium of
F. subglutinans (g), chlamydospores of FGSC (h), conidiophores
of F. proliferatum (i)
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Table 3 Morphological characters of Fusarium isolates from different cultivars of wheat (Triticum aestivum L.)
Name of the
Species
Pigmentation Growth Chlamydospore Sporodochium
on PDA
rate
Microconidia Macroconidia
Number Apical cell Basal size (μm)
of septa
cell
FGSC
F. culmorum
vary from
white to
pale pink
to red
red
F. subglutinans initially
white but
becomes
violet
F. proliferatum purple-violet
R
+
Pale orange
–
5–7
tapered
Fs
24–72 × 4–
7
R
+
Orange to
brown
–
3–4
Nfs
37–55 × 4–
7
S
–.
Tan to
orange
+
3
rounded
and
blunt
curved
Pfs
54–85 × 4–
7
S
–
Tan to pale
orange
+
3–5
curved
Pf
54–85× 4–
7
FGSC: Fusarium graminearum species complex, R: Rapid, S: Slow, +: Presence, −: Absence, Fs: Foot shape, Nfs: Notched and without a
distinct foot shape, Pfs: Relatively poorly developed, Pf: Poorly developed
isolates morphologically identified as FGSC, 24 isolates
belonged to F. graminearum, three isolates were
F. meridionale and one isolates was F. asiaticum. All
six isolates morphologically identified as
F. proliferatum, were confirmed using PRO1-F/PRO1R primers. All four isolates morphologically identified
as F. culmorum were confirmed using OPT18-F470/
OPT18-R470 primers. Also, morphological identification of three isolates belonging to F. subglutinans was
confirmed using OPT18-61-2 F/61-2R primers specific
for this species.
Trichothecene genotype detection by PCR
The gene Tri5 encodes Trichodiene synthase, which
catalyses the first step in trichothecene biosynthesis. In
this study, this gene was detected using the primer set
TRI5(F)/TRI5(R), which produces a unique PCR product in size of 544 bp for strains that contain Tri5 gene
(Doohan et al. 1999; Covarelli et al. 2014). In overall,
results obtained from PCR of the tri5 gene showed
amplification of this gene for 78.1 % of trichothecene
producing and 21.9 % of non-trichothecene producing
isolates.
Also, primers for amplification of five genomic regions (Tri3, Tri5-Tri6 intergenic, Tri7, Tri12 and Tri13)
involved in trichothecene biosynthesis were used
(Table 2). The results obtained from PCR reaction with
Tri3, Tri5-Tri6 intergenic, Tri12 and Tri13 showed the
presence of NIV genotype in our isolates. Primers used
in regions of Tri3, Tri5-Tri6 intergenic, Tri12 and Tri13
produced a fragment of 840, 360, 415 and 840 bp
length, respectively. The Tri7 primer pair which was
specific for detecting DON produced a fragment of
483 bp length. Primers Tri3 and Tri12 for detecting 3ADON produced fragments of 243 and 410 bp length,
respectively, and for detecting 15-ADON produced
fragments of 610 and 670 bp length, respectively. The
results showed that 25 isolates had the NIV genotype,
five classified in 3-ADON genotype, two had 15ADON genotype, and nine were non-trichothecene producing isolates (Table 4). There were negative results
with all genotype-specific primers in Table 4.
Distribution of genotypes
Among different wheat samples of various cultivars in
the investigated regions, Galikesh farms showed high
distribution of NIV producer isolates. This trichothecene genotype was detected in all sampling regions.
Among the isolates, 3-ADON was detected from different fields of Gorgan, Azadshar, Ali Abad, Bandar gaz
and Agh Ghala, while 15-ADON was detected from
different fields of Gorgan and Agh Ghala in the northern
region of Iran. Also we observed isolates, which based
on PCR assay results should be able to produce NIV,
DON, 3-ADON and/or 15 A-DON simultaneously
(Table 4).
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Table 4 Isolates, origin, species-specific PCR, presence of trichothecene-specific markers detected by TRI-based multiplex PCR assays and trichothecene genotype
Isolate
code
Cultivar
Sample site Species-specific
PCR
Trichothecene
genotype
PCR assay results
Tri5 Tri3
Tri5-Tri6
Tri7
Tri12
Tri13
Tri
P
15-ADON 3-ADON NIV DON NIV DON NIV 15-ADON 3-ADON DON NIV
FH1
Koohdasht Gorgan
F. graminearum
NIV
+
+
+
+
−
−
−
+
−
+
−
+
FH2
Unknown
Gorgan
F. graminearum
NIV
+
−
−
+
−
−
−
+
−
−
−
−
FH3
Unknown
Gorgan
F. graminearum
NIV
+
−
−
+
−
−
−
+
+
−
−
−
FH4
Tajan
Gorgan
F. meridionale
3-ADON
+
−
+
−
−
−
−
−
−
−
−
−
Tajan
Gorgan
F. graminearum
15-ADON
+
+
−
−
−
−
−
−
−
−
+
−
Unknown
Gorgan
F. meridionale
NIV
+
−
−
−
−
−
−
+
−
+
−
−
FH7
N8720
Gorgan
F. subglutinans
NIV
+
−
+
−
−
−
−
+
−
−
−
+
Tajan
Azadshar
F. proliferatum
NIV
+
−
+
+
−
−
−
−
+
−
−
−
Tajan
Azadshar
F. culmorum
NIV
+
−
−
+
−
−
−
−
+
−
−
−
FH10
Unknown
Azadshar
F. graminearum
3-ADON
+
−
−
−
−
−
−
−
−
+
+
−
FH11
Tajan
Minoodasht F. graminearum
−
−
−
−
−
−
−
−
−
−
−
−
−
FH12
Tajan
Minoodasht F. graminearum
NIV
+
−
−
+
−
−
−
−
−
−
−
+
FH13
Unknown
Minoodasht F. graminearum
NIV
+
−
−
−
−
+
−
+
−
−
−
+
FH14
Gonbad
Minoodasht F. proliferatum
−
−
−
−
−
−
−
−
−
−
−
−
−
FH15
Tajan
Minoodasht F. proliferatum
NIV
+
−
−
−
−
+
−
−
−
−
−
+
FH16
Koohdasht Ali Abad
F. graminearum
3-ADON
+
−
+
−
−
−
+
−
−
−
−
−
FH17
Tajan
Ali Abad
F. graminearum
−
−
−
−
−
−
−
−
−
−
−
−
−
FH18
Tajan
Ali Abad
F. graminearum
NIV
+
−
+
+
−
−
−
−
−
−
−
−
FH19
N8720
Galikesh
F. proliferatum
−
−
−
−
−
−
−
−
−
−
−
−
−
FH20
N8720
Galikesh
F. proliferatum
NIV
+
−
+
+
−
−
−
−
−
−
−
−
FH21
N8720
Galikesh
F. proliferatum
NIV
+
−
−
+
−
−
−
−
−
+
−
−
FH22
Unknown
Galikesh
F. graminearum
NIV
+
−
−
−
−
+
−
+
−
−
−
−
F. culmorum
FH23
Unknown
Galikesh
NIV
+
−
−
+
−
−
−
−
−
+
−
+
FH24
Tajan
Bandar gaz F. graminearum
3-ADON
+
−
−
−
−
−
−
−
−
+
+
−
FH25
Unknown
Bandar gaz F. graminearum
NIV
+
−
−
+
−
−
−
+
−
−
−
+
FH26
Gonbad
Daland
F. graminearum
NIV
+
−
−
+
−
−
−
−
−
−
−
+
FH27
Koohdasht Daland
F. graminearum
−
−
−
−
−
−
−
−
−
−
−
−
−
FH28
Koohdasht Daland
F. asiaticum
−
−
−
−
−
−
−
−
−
−
−
−
−
Eur J Plant Pathol (2017) 147:897–918
FH8
FH9
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FH5
FH6
Isolate
code
Cultivar
Sample site Species-specific
PCR
Trichothecene
genotype
PCR assay results
Tri5 Tri3
Tri
P
Tri5-Tri6
Tri7
Tri12
Tri13
15-ADON 3-ADON NIV DON NIV DON NIV 15-ADON 3-ADON DON NIV
Tajan
Agh Ghala
F. graminearum
NIV
+
−
+
−
−
−
−
+
−
−
−
−
FH30
Tajan
Agh Ghala
F. graminearum
NIV
+
+
−
+
−
−
−
+
−
−
−
−
FH31
Unknown
Agh Ghala
F. meridionale
NIV
+
−
−
−
−
−
−
+
−
+
−
−
FH32
Unknown
Agh Ghala
F. graminearum
3-ADON
+
−
+
−
−
−
+
−
−
−
+
−
FH33
Koohdasht Agh Ghala
F. graminearum
NIV
+
−
−
+
−
−
−
−
−
−
−
+
FH34
Koohdasht Agh Ghala
F. graminearum
15-ADON
+
+
−
−
+
−
−
−
−
−
−
−
FH35
Koohdasht Ismail
Abad
Unknown Ismail
Abad
Unknown Ismail
Abad
Tajan
Kordkuy
F. subglutinans
−
−
−
−
−
−
−
−
−
−
−
−
−
F. graminearum
−
−
−
−
−
−
−
−
−
−
−
−
−
F. culmorum
−
−
−
−
−
−
−
−
−
−
−
−
−
F. graminearum
NIV
+
−
−
−
−
−
−
−
−
−
−
+
FH39
Tajan
Kordkuy
F. culmorum
NIV
+
−
−
−
−
−
−
+
−
−
−
+
FH40
Unknown
Fazel Abad F. subglutinans
NIV
+
+
−
+
−
−
−
−
−
−
−
−
FH41
Unknown
Fazel Abad F. graminearum
NIV
+
−
−
−
−
−
−
+
−
−
−
−
FH36
FH37
FH38
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FH29
Eur J Plant Pathol (2017) 147:897–918
Table 4 (continued)
Tri P: trichothecene producers, +: Presence, −: Absence, 3ADON: 3-acetyldeoxynivalenol + deoxynivalenol, 15ADON, 15-acetyldeoxynivalenol + deoxynivalenol, NIV:
nivalenol + acetylated derivatives (Miller et al. 1991; Ward et al. 2002)
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Mycotoxin analysis
Virulence and aggressiveness assay
Data of trichothecene production by Fusarium isolates
on rice medium are shown in Table 5. For FGSC,
53.6 %, 28.6 %, 42.9 % and 21.4 % of the analysed
samples contained NIV, DON, 3-ADON and 15ADON, in levels ranging from 437 to 1205 μg kg−1;
269 to 1248 μg kg−1; 178 to 1183 μg kg−1 and 240 to
1155 μg kg−1, respectively. Most of the F. culmorum,
F. proliferatum and F. subglutinans isolates were NIV
producers (75 %, 66.7 % and 66.7 %), at levels between
700 and 1075 μg kg−1, 260 and 1199 μg kg−1 and 313 to
1202 μg kg−1, respectively (Table 5). Isolates FH1 of
F. graminearum and FH8 of F. proliferatum produced
NIV, 3-ADON and 15-ADON simultaneously (Table 5).
Comparison of the data obtained from inoculation of
Fusarium isolates on wheat seedlings, wheat spikes and
leaf segments revealed that different isolates tested had
various virulence capabilities (Table 6). Based on the
results obtained, significant differences in disease index
on seedlings, wheat spikes and also leaf lesion length
were observed among isolates tested.
Pathogenicity tests on seedlings showed that the
lowest disease index was observed for the FH11
isolate. The FH1 isolate caused the highest level
of disease progress on seedlings with average DI
of 63 ± 1.2 (Table 6, Fig. 3a). The results of pathogenicity test on wheat spikes showed that the
longest lesions were produced by FH1 isolate with
an average DI of 69.3 ± 0.3 (Table 6, Fig. 3b). The
shortest lesions were produced by FH11 and FH19
isolates among all Fusarium isolates. FHB index
of other isolates ranged from 66.3 ± 1.3 to 12.7
± 0.3. Leaf assay revealed that the highest lesion
length was produced by the FH1 isolate. The
lowest lesion length was produced by FH19 and
FH28 isolates, respectively. Other isolates tested
fell between these with various levels of virulence
on wheat leaf segments (Table 6, Fig. 3c).
The results of aggressiveness test on seedlings, wheat
spikes, and detached-leaves showed earlier development of disease symptoms by FH1 isolate compared to
other isolates tested (Table 6).
Analysis CWDEs activity
Analysis of CWDEs showed that all Fusarium isolates were capable of producing CWDEs. According
to the results obtained, for most of the isolates tested
the maximum levels of cellulase, xylanase, pectinase
and lipase activity were observed at 72, 96, 144 and
192 h post-culturing (hpc) on liquid medium, respectively. Then, the activity decreased gradually
with time, until it remained at constant levels at
the end of culture time. At the time point in which
most of the isolates showed maximum activity for
each enzyme, the level of CWDEs activity among
isolates varied from 232 to 938 μg ml−1 for cellulase, 589 to 1215 μg ml−1 for xylanase, 3340 to
4695 μg ml−1 for pectinase, and 13 to 28 μg ml−1
for lipase (Table 5).
The FH1 and FH8 isolates showed the maximum
cellulase activity in vitro among all isolates. The
lowest cellulase activity was observed for FH17
and FH36 isolates, respectively. The lowest xylanase
activity belonged to FH19 and FH11 isolates, and
also maximum xylanase activity with 1215 ± 7.1 and
1187 ± 11.3 μg ml−1, respectively, was observed for
FH1 and FH8 isolates. With regard to pectinase,
FH8, FH29, FH7 and FH1 isolates showed the maximum cellulase activity. The lowest pectinase activity belonged to FH11, FH19, FH37 and FH28 isolates, respectively. Maximum lipases activity was
observed for FH1 and FH8 isolates, respectively
and the isolates FH37 and FH11 had the lowest
lipase activity (Table 5).
Correlation between activity of CWDEs and virulence
We compared the activity of CWDEs produced by
some of the Fusarium isolates, which caused maximum or minimum level of virulence on wheat
leaves, seedlings, or spike (Fig. 4) for finding possible association between CWDEs and virulence.
The isolates FH1 and FH8, which showed the
highest levels of virulence in three different bioassays on leaf, seedling and spike, had considerably
higher levels of enzyme activity at various time
points investigated. Whereas, the isolates FH11 of
F. graminearum and FH19 of F. proliferatum, which
had the lowest virulence capability (on wheat leaf,
spike and seedling), revealed the lowest level of
CWDEs activity at most of the time points tested
(Fig. 4).
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Eur J Plant Pathol (2017) 147:897–918
909
Table 5 Mycotoxin production by Fusarium isolates in rice cultures analyzed by GC-MS and maximum of enzyme activity
Isolate code Trichothecene production in vitro (μg kg−1)
NIV
3-ADON
15-ADON
DON
Maximum of enzyme activity (μg ml−1)
Cellulase 72 hpc Xylanase 96 hpc Pectinase 144 hpc Lipases 192 hpc
FH1
910
498
253
ND
938 ± 2.8 a
4620 ± 6.3 a
29 ± 0.9 a
FH2
1105
ND
ND
ND
488 ± 0.4 g
1215 ± 7.1 a
833 ± 8.0 kl
4255 ± 3.8 f
23 ± 0.6 d
FH3
1007
243
ND
ND
618 ± 21.7 f
950 ± 3.6 efg
4295 ± 5.2 ef
24 ± 0.2 d
FH4
ND
501
ND
1248
725 ± 0.8 c
823 ± 4.6 l
3558 ± 16.7 h
20 ± 0.5 fg
FH5
ND
ND
1001
1000
672 ± 19.6 d
876 ± 5.6 ij
4253 ± 4.6 f
24 ± 0.9 d
FH6
499
108
ND
ND
633 ± 4.0 ef
890 ± 10.8 hi
FH7
1202
308
ND
ND
667.8 ± 5.9 d
FH8
438
997
240
ND
FH9
751
ND
325
FH10
ND
1098
FH11
–
–
FH12
754
FH13
FH14
FH15
4324 ± 6.8 ef
16 ± 0.2 h
1041 ± 3.8 c
4620 ± 6.3 a
27 ± 0.5 b
930 ± 7.8 a
1187 ± 11.3 a
4695 ± 33.3 a
28 ± 0.5 a
ND
770 ± 25.2 bc
1001 ± 5.4 cd
4597 ± 39.1 b
26.8 ± 0.2 b
ND
269
630 ± 2.3 ef
820 ± 12.6 l
3553 ± 21.3 h
–
–
324 ± 8.8 j
620 ± 10.8 pq
3375 ± 21.3 i
13 ± 0.5 i
ND
ND
ND
670 ± 0.4 d
871 ± 13.5 ijk
4259 ± 9.3 f
23 ± 2.5 d
620
ND
ND
ND
649 ± 0.6 de
843 ± 15.3 jkl
3711 ± 6.5 1 g
23 ± 0.6 d
–
–
–
–
452 ± 1.3 h
725 ± 20.0 mno
3519 ± 16.0 h
19 ± 0.1 g
1199
ND
ND
ND
628 ± 6.2 ef
1008 ± 14.3 cd
4452 ± 35.4 bc
24 ± 0.0 d
FH16
ND
1030
ND
1023
599 ± 6.1 f
827 ± 13.5 l
3584 ± 10.4 h
22 ± 0.4 de
FH17
–
–
–
–
232 ± 5.0 k
650 ± 4.6 p
3517 ± 14.2 h
19 ± 0.1 g
FH18
701
315
ND
ND
723 ± 1.0 c
911 ± 1.2 ghi
3726 ± 8.82 g
20 ± 0.0 fg
589 ± 16.4 q
20 ± 0.2 fg
FH19
–
–
–
–
378 ± 2.1 i
3367 ± 4.4 i
16 ± 0.3 h
FH20
1098
974
ND
ND
732 ± 20.8 c
1094 ± 1.3 b
4426 ± 18.2 c
26 ± 0.0 b
FH21
260
1089
ND
ND
824 ± 7.4 b
1001 ± 7.8 d
4413 ± 41.5 cd
24 ± 0.0 d
FH22
1001
ND
ND
ND
726 ± 3.6 c
4323 ± 47.5 ef
24 ± 0.1 d
FH23
806
355
ND
ND
649 ± 25.3 de
898 ± 9.2 hi
4354 ± 4.4 ef
FH24
ND
279
ND
1077
673 ± 10.2 d
825 ± 5.4 l
3577 ± 45.3 h
22 ± 0.3 de
FH25
739
ND
ND
ND
738 ± 2.0 c
896 ± 5.6 hi
4345 ± 24.7 de
24 ± 1.2 d
FH26
437
ND
ND
ND
686 ± 14.6 d
929 ± 27.8 fgh
4267 ± 22.5 ef
24 ± 0.9 cd
FH27
–
–
–
–
497 ± 1.2 g
752 ± 11.9 mn
3577 ± 44.4 h
20 ± 0.1 fg
FH28
–
–
–
–
475 ± 0.4 gh
704 ± 17.8 o
3340 ± 3.8 i
16 ± 0.1 h
FH29
1230
1183
ND
ND
726 ± 3.6 c
1012 ± 0.2 cd
FH30
480
ND
1155
ND
678 ± 36.6 d
FH31
1211
980
ND
ND
712 ± 5.2 c
FH32
ND
178
ND
895
611 ± 17.2 f
759 ± 13.4 m
3544 ± 33.3 h
20 ± 0.0 fg
FH33
494
ND
ND
ND
725 ± 0.8 c
828 ± 0.8 l
3508 ± 7.12 h
19 ± 0.5 g
FH34
ND
ND
293
1000
632 ± 13.8 ef
730 ± 20.5 mno
3511 ± 9.61 h
19 ± 0.2 fg
FH35
-
–
–
–
296 ± 18.5 j
706 ± 17.3 o
3510 ± 10.0 h
19 ± 0.3 g
FH36
–
–
–
–
254 ± 12.3 k
714 ± 20.5 no
3563 ± 23.9 h
FH37
–
–
–
–
249 ± 10.9 k
646 ± 7.7 p
3350 ± 45.1 i
FH38
1088
ND
ND
ND
629 ± 20.9 ef
874 ± 2.1 ig
3568 ± 29.2 h
21 ± 0.5 ef
FH39
1075
ND
ND
ND
725 ± 0.8 c
884 ± 12.1 i
3576 ± 28.4 h
20 ± 0.0 fg
FH40
313
ND
1088
ND
725 ± 0.8 c
940 ± 5.7 fg
4287 ± 5.8 ef
24 ± 0.5 d
FH41
1205
1180
ND
ND
614 ± 5.0 f
958 ± 36.1 ef
4402 ± 54.9 cd
26 ± 0.0 bc
974 ± 2.0 de
961 ± 10.5 ef
1080 ± 8.2 b
24.4 ± 1.6 d
4620 ± 6.3 a
26 ± 0.4 bc
3585 ± 42.5 h
20 ± 0.2 fg
4510 ± 21.8 b
26 ± 0.3 b
20 ± 0.1 fg
12.9 ± 0.4 i
ND: not detected, −: without genotype of trichothecene biosynthesis. Average ± standard error, Different letters indicate significant
differences according to Duncan analysis using SPSS software (P = 0.05), each experiment was repeated two times with similar results
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Table 6 Virulence and aggressiveness of Fusarium isolates on seedling, wheat spike and leaf segments inoculated
Isolate
code
Virulence and aggressiveness analysis
leaf
FH1
FH2
FH3
FH4
FH5
FH6
FH7
FH8
FH9
FH10
FH11
FH12
FH13
FH14
FH15
FH16
FH17
FH18
FH19
FH20
FH21
FH22
FH23
FH24
FH25
FH26
FH27
FH28
FH29
FH30
FH31
FH32
FH33
FH34
FH35
FH36
FH37
FH38
FH39
FH40
FH41
seedling
spike
Virulence
(LL, mm)
Aggressiveness
(hpi)
Virulence (DI)
Aggressiveness
(hpi)
Virulence
(FHB index)
Aggressiveness
(hpi)
39 ± 1.1 a
29 ± 1.6 fg
30.5 ± 1.9 efg
18 ± 0.0 i
23.75 ± 0.6 h
29 ± 1 fg
33.25 ± 1.2 cde
37 ± 0.8 ab
31 ± 0.9 ef
19 ± 1.3 i
7.75 ± 0.94 lm
29.25 ± 1.6 fg
29.5 ± 0.5 fg
10.25 ± 0.7 kl
30 ± 0.8 efg
20 ± 0.7 i
11 ± 0.6 kl
29 ± 1 fg
5.75 ± 0.6 m
36.5 ± 0.9 abc
32 ± 1.2 def
29.5 ± 0.6 fg
29 ± 1.1 fg
19.25 ± 0.5 i
28.25 ± 1.0 g
29.75 ± 0.5 fg
15 ± 0.4 j
6.75 ± 1.7 m
34.5 ± 1.5 bcd
29.25 ± 1.2 fg
35.5 ± 1.0 bc
19.75 ± 1.2 i
29 ± 1.2 fg
25 ± 1.1 h
12.5 ± 1.0 j
10 ± 0.4 kl
5.75 ± 0.6 m
30 ± 1.9 efg
28.5 ± 0.5 fg
29.5 ± 1.3 fg
29.75 ± 0.6 fg
12
48
48
72
60
48
36
24
48
72
96
48
48
96
60
72
96
48
108
24
36
48
48
72
60
48
96
108
24
48
24
72
48
72
96
96
108
48
48
48
48
63 ± 1.2 a
32 ± 1.0 hijk
33 ± 0.7 ghij
20 ± 0.6 no
27 ± 0.3 m
35 ± 0.3 efg
37 ± 0.3 cd
40 ± 0.3 b
35 ± 0.3 efg
18 ± 0.6 p
4 ± 0.6 s
31 ± 0.3 jk
31 ± 0.3 jk
10 ± 0.6 q
35 ± 0.3 ef
22 ± 0.9 n
8 ± 0 qr
34 ± 0.6 efgh
9 ± 1.7 qr
39 ± 0.7 bc
36 ± 0.3 de
34 ± 0.3 efghi
34 ± 0.6 ghij
18 ± 0.7 op
33 ± 0.3 ghij
32 ± 0.7 ijk
10 ± 0.6 q
7 ± 0.6 r
38 ± 0.3 bc
35 ± 0.6 ef
39 ± 0.6 bc
21 ± 0.7 n
31 ± 1.0 jk
28 ± 0.6 l
9 ± 0.7 q
9 ± 1.1 qr
9.3 ± 0.6 qr
30 ± 0.6 k
33 ± 0.3 ghij
33 ± 0.7 ghij
33 ± 0.4 ghi
72
168
168
216
216
144
96
72
144
228
264
180
180
240
144
216
240
144
240
84
108
168
180
216
180
180
228
240
96
120
96
216
180
216
240
240
240
180
168
168
168
69.3 ± 0.3 a
29.7 ± 0.3 gh
30 ± 2.3 gh
24.3 ± 2.7 ij
41 ± 1.2 cd
42.3 ± 2.6 cd
42 ± 2.5 cd
52.7 ± 2.8 b
42 ± 0 cd
18.3 ± 4.3 kl
7 ± 2.3 n
21.3 ± 1.3 jk
27.7 ± 0.3 hi
16. ± 0.6 lm
42 ± 0 cd
27 ± 0 hi
16.3 ± 2.4 lm
31 ± 1 fgh
7.3 ± 0.3 n
68.7 ± 0.9 a
43.3 ± 0.3 c
30.7 ± 0.9 fgh
45.3 ± 0.3 c
14.3 ± 0.9 lm
38.3 ± 0.9 de
45.7 ± 0.3 c
13 ± 0.6 m
14.3 ± 0.7 lm
66.3 ± 1.3 a
43.3 ± 0.7 c
45 ± 1.1 c
16 ± 0 lm
36 ± 3 e
29 ± 0.6 hi
12.7 ± 0.3 m
29.3 ± 1.3 h
12.7 ± 0.3 m
34.3 ± 0.3 efg
26.3 ± 0.3 hi
26.3 ± 0.3 hi
35.3 ± 1.2 ef
48
120
120
144
120
72
72
60
84
156
180
168
120
168
72
120
168
120
180
60
72
120
72
168
72
72
168
168
60
72
72
168
120
144
168
144
168
120
144
144
120
hpi: hours post inoculation, LL: Lesion length, DI: Disease index, FHB index: Fusarium head blight index. Average ± standard error,
Different letters indicate significant differences according to Duncan analysis using SPSS software (P = 0.05), each experiment was repeated
two times with similar results
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911
Fig. 3 Disease symptoms on wheat seedlings (a), spikes (b) and leaf (c) by Fusarium isolates. Control, F. graminearum (FH1) and
F. proliferatum (FH8). Arrows marked symptoms disease and necrotic lesions
Fig. 4 Analysis activities of CWDEs produced by Fusarium
isolates over an incubation maximum period of 240 h. cellulase
activity (a), xylanase activity (b), pectinase activity (c) and lipase
activity (d). Values are means of 3 replicates.
FH8;
FH11;
FH19;
FH29
FH1;
FH20;
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912
Discussion
In this study, to identify and determine the frequencies
of Fusarium spp. causing wheat head blight in northern
region of Iran, a total of 41 Fusarium spp. isolates were
obtained from infected wheat heads showing disease
symptoms such as ear blight and bleached grains and
the isolates were characterized using morphological and
molecular methods. Morphological identification was
confirmed using a set of species-specific primers. This
is the first detailed report of trichothecene genotypes in
populations of Fusarium spp. collected from the northern region of Iran and quantification of trichothecenes
using GC-MS. Also, we evaluated the activities of
CWDEs, which are involved in plant-pathogen interactions during FHB infection and investigated the correlation between virulence factors, aggressiveness and
virulence capability of Fusarium isolates on seedlings,
spikes and leaves of wheat plants.
Based on morphological observations, a total of 41
isolates belonging to four Fusarium species were isolated from wheat grain samples. Twenty eight isolates were
identified as FGSC, six isolates as F. proliferatum, three
isolates as F. subglutinans and one isolate as
F. culmorum. The FHB disease was observed in different regions of Golestan province. Gorgan and Agh
Ghala showed the highest percentage of infected samples. It is possible that planting the sensitive cultivar
Tajan and crop rotation with maize and sorghum are the
causes of FHB prevalence in this region (Table 4). The
main species associated with FHB disease are
F. graminearum, F. culmorum and F. proliferatum,
among which F. graminearum and F. proliferatum are
known to produce toxins (Karami-Osboo et al. 2010).
Davari et al. (2013) reported that 96 % of the isolates
recovered from FHB affected wheat in Ardabil province
of Iran belong to F. graminearum, which is in accordance with our data.
The results of morphological identification were in
accordance with the reports of Sarver et al. (2011) and
Starkey et al. (2007). F. graminearum formed narrow
conidia with 4.0–4.5 μm width, similar to F. asiaticum.
But, the width of F. meridionale isolates was less than
4.5 μm. F. graminearum and F. asiaticum did not form
beaked conidia in contrast to F. meridionale. Conidia of
F. graminearum and F. asiaticum, however, were gradually curved and, in addition, those were most frequently widest above the mid-region. In contrast, conidia of
F. meridionale were gradually curved and most
Eur J Plant Pathol (2017) 147:897–918
frequently widest at the mid-region (Sarver et al. 2011;
Starkey et al. 2007).
Species-specific PCR analysis showed that among 41
isolates used in this study, 24 isolates were identified as
F. graminearum, six were F. proliferatum, four were
F. culmorum, three were F. meridionale, three were
F. subglutinans and one isolate of F. asiaticum was
identified. The products of DNA amplification
corresponded to sizes reported for species-specific
PCR products and confirmed the morphological identification (Alkadri et al. 2013; Castañares et al. 2014;
Williams et al. 2002). Based on our molecular analysis,
morphological identification of all 4 isolates belonging
to F. culmorum was confirmed using the OPT18-F470/
OPT18-R470 primers and gave a PCR product of about
472 bp. But according to Schilling et al. (1996), this
primer pair does not give a positive signal with all
F. culmorum isolates.
Results of the present study indicated that
F. graminearum s.s. was the most frequently isolated
species (58.6 %), confirming other reports on this species as one of the most often isolated Fusarium species
from the FGSC not only in Iran (Haratian et al. 2008),
but also in many other countries including the United
States (Schmale et al. 2011; Alvarez et al. 2011; Prodi
et al. 2011).
The Tri5 gene encodes trichothecene synthase as the
initial product in the trichothecene biochemical pathway
(Neissen and Vogel 1997), which could be used for
developing a PCR-based assay to detect trichotheceneproducing Fusarium species (Doohan et al. 1999). The
results of trichothecene genotype detection revealed
83.4, 66.7, 75, 66.7 and 100 % amplification of the
tri5 gene for the isolates belonging to F. graminearum,
F. proliferatum, F. culmorum, F. subglutinans and
F. meridionale, respectively. The isolate of
F. asiaticum did not produce trichothecene.
Production of NIV required Tri13 and Tri7 genes
that produce the acetylation and oxygenation of the
oxygen at C-4 to produce nivalenol and 4-acetyl
nivalenol, respectively (Lee et al. 2009). Our results
showed that NIV was produced by 60.9 % of the
isolates. Whereas, 41.5 % of the isolates produced
3-ADON, 17.1 % 15-ADON, and 17.1 % DON. In
most isolates, NIV was found simultaneously with
3-ADON and 15-ADON. Except for 16 isolates,
NIV was always produced in larger amounts than
the other trichothecenes. Our data are in accordance
with observations of Gale et al. (2011), which
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Eur J Plant Pathol (2017) 147:897–918
reported that the NIV chemotype was prevalent on
wheat in Southern Louisiana.
Trichothecene genotype detection of the FGSC population showed that the NIV genotype was the most
frequent (57.2 %) followed by 3-ADON (17.9 %) and
15-ADON (7.2 %) genotypes. With regard to
F. proliferatum and F. subglutinans the analysis showed
only presence of the NIV (66.7 %) and absence of 3ADON and 15-ADON chemotypes. Two isolates of
F. culmorum belonged to the NIV genotype. So, investigation of trichothecene chemotypes revealed that the
NIV chemotype was the most prevalent in Fusarium
isolates obtained from wheat farms of the northern region of Iran, followed by 3-ADON and 15-ADON
chemotypes. Similar results were obtained by AbediTizaki and Sabbagh (2013). Also, Haratian et al. (2008)
reported that the NIV chemotype was dominant in
Mazandaran province in the northern part of Iran. Results similar to our findings were obtained in southern
Louisiana (Gale et al. 2011), England and Wales
(Jennings et al. 2004), Netherlands (Waalwijk et al.
2003) and South Africa (Sydenham et al. 1989). Observation of a wide variation in trichothecene production
in vitro among Fusarium isolates in this study was
supported by results reported by other investigators
using GC-MS analysis (Alvarez et al. 2009; Covarelli
et al. 2014).
Wheat and maize in rotation with sorghum are the
most important cereal crops in the northern region of
Iran. Crop rotation may influence the pathogen population dynamics, especially since it was shown that
NIV and DON act as virulence factors on wheat,
while only the NIV chemotype is virulent on maize
(Maier et al. 2006). Our results showed that in the
north of Iran, which is an important region in producing small grain cereal crops such as wheat and
rice, FHB-associated F. graminearum isolates produced mostly NIV rather than DON derivatives.
This finding is in accordance with observations of
Davari et al. (2013), who demonstrated association
of the NIV chemotype with local rice production.
Other studies have also clearly shown this association between rice production and the prevalence of
the NIV chemotype (Umpiérrez-Failache et al. 2013;
Qiu and Shi 2014; Van der Lee et al. 2015), which
confirmed our data. According to these results, it
might be concluded that differences in crop rotations
and bordering crops may influence the species and
chemotypes found in wheat.
913
In general, NIV chemotypes appeared to be more aggressive than the other chemotypes of F. graminearum.
This finding is in agreement with the observations of other
researchers (Carter et al. 2002; Cumagun et al. 2004). In
addition, Fusarium isolates producing higher level of NIV
and 3-ADON chemotypes were more aggressive than
other isolates. Similarly, Von der Ohe et al. (2010)
demonstratd that the isolates with 3-ADON chemotype
were more aggressive than those with 15-ADON. Also,
Puri and Zhong (2010) suggested that the 3-ADON isolates were more aggressive and caused higher FHB
severity.
Evaluating the activities of CWDEs, which are involved in the infection process of FHB pathogens on
wheat, was performed in this study. Aggressiveness of
Fusarium spp. involves different mechanisms such as
production of extracellular enzymes and mycotoxins
(Ortega et al. 2013). Hemibiotrophic (F. graminearum)
and necrotrophic (F. subglutinans, F. proliferatum and
F. culmorum) pathogens often produce different extracellular CWDEs (Stankovic et al. 2007). These enzymes
are particularly important for phytopathogenic fungi
without specialized penetration structures (Gibson
et al. 2011). We focused on detailed investigation of
pectinase, cellulase, xylanase and lipase activities in
different time points because they are the major CWDEs
in Fusarium species (Kikot et al. 2009; Ortega et al.
2013). During 10 days of CWDEs investigation, production rate and time of reaching each enzyme to its
maximum activity varied among different isolates. Cellulase was the first in reaching its peak, while the maximum activity of xylanase, lipase and pectinase appeared later and at lower magnitude. Similar results
were obtained by Ortega et al. (2013), who reported that
lipase activity reached to its maximum activity after
longer incubation time compared to other enzymes tested. Comparing CWDEs activities and virulence of the
isolates revealed that lipase and pectinase had less effect
on virulence compared to cellulase and xylanase. Similar results were reported by Phalip et al. (2005), who
analyzed exo-proteome of F. graminearum grown on
plant cell wall.
The results of our study about virulence of Fusarium
isolates on seedlings, wheat spikes and leaf segments
showed that all isolates were pathogenic on wheat (cv.
Falat) and differences in virulnce capability were found.
According to the results reported by other investigators,
strong association has been found between the severity
of FHB and mycotoxin concentration (Panthi et al.
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914
2014; Hernandez-Nopsa et al. 2014; Wegulo 2012;
Burlakoti et al. 2007) as observed in this study.
F. graminearum isolates without the ability of producing
trichothecenes were unable to cause severe disease on
wheat tissues, which was in agreement with the data of
Bai et al. (2002). Our results are in accordance with
several other studies showing that trichothecenes have
a significant role in determining the virulence of Fusarium isolates (Hernandez-Nopsa et al. 2014; Purahong
et al. 2013; Umpiérrez-Failache et al. 2013).
Since the NIV chemotype is more detrimental for
consumers, we have to find a solution to reduce this
mycotoxin. The economic and social impact of FHB
highlights the necessity of using effective control strategies. Management of FHB to reduce mycotoxin contamination have been developed by utilizing host resistance, use of biological agents, tillage, seed treatment,
crop rotation and fungicides application during
flowering stage (Brown et al. 2007; Müllenborn et al.
2008; Willyerd et al. 2012; Hollingsworth et al. 2008).
Knowledge on Fusarium species and chemotypes,
CWDEs and virulence levels could be useful in the
production of resistant varieties and other management
strategies to reduce destructive effects of FHB disease in
small grain cereals, especially in wheat growing areas.
Acknowledgments We thank Ferdowsi University of Mashhad,
Iran, for financial support of this research with project number
3/31477 approved on 2/07/2014.
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