RESEARCH ARTICLE
Fitness of three Fusarium pathogens of wheat
Berna Tunali1, Friday Obanor2, Gul Erginbaş3, Rhyannyn A. Westecott2, Julie Nicol4 & Sukumar
Chakraborty2
1
Department of Plant Pathology, Ondokuz Mayis University, Samsun, Turkey; 2CSIRO Plant Industry, St Lucia, Qld, Australia; 3Department of
Biology, Eskisehir Osmangazi University, Eskisehir, Turkey; and 4CIMMYT International, Ankara, Turkey
Correspondence: Sukumar Chakraborty,
CSIRO Plant Industry, 306 Carmody Road, St
Lucia, Qld 4067, Australia. Tel.: +61 7 3214
2677; fax: +61 7 3214 2950; e-mail:
[email protected]
Received 30 January 2012; revised 3 April
2012; accepted 4 April 2012.
Final version published online 3 May 2012.
DOI: 10.1111/j.1574-6941.2012.01388.x
Editor: Wietse de Boer
MICROBIOLOGY ECOLOGY
Keywords
pathogen aggressiveness; mycotoxin
production; saprophytic fitness.
Abstract
Crown rot and head blight of wheat are caused by the same Fusarium species.
To better understand their biology, this study has compared 30 isolates of the
three dominant species using 13 pathogenic and saprophytic fitness measures
including aggressiveness for the two diseases, saprophytic growth and fecundity
and deoxynivalenol (DON) production from saprophytic colonization of grain
and straw. Pathogenic fitness was generally linked to DON production in
infected tissue. The superior crown rot fitness of Fusarium pseudograminearum
was linked to high DON production in the stem base tissue, while Fusarium
culmorum and Fusarium graminearum had superior head blight fitness with
high DON production in grains. Within each species, some isolates had similar
aggressiveness for both diseases but differed in DON production in infected tissue to indicate that more than one mechanism controlled aggressiveness. All
three species produced more DON when infecting living host tissue compared
with saprophytic colonization of grain or straw, but there were significant links
between these saprophytic fitness components and aggressiveness. As necrotrophic pathogens spend a part of their life cycle on dead organic matter, saprophytic fitness is an important component of their overall fitness. Any
management strategy must target weaknesses in both pathogenic fitness and
saprophytic fitness.
Introduction
In population, biology fitness is widely used as a measure of survival and reproductive success of an entity
such as an allele, individual or group. Malthusian fitness,
which essentially describes instantaneous growth rate, is
a convenient way to measure fitness of microorganisms
such as bacteria (Pringle & Taylor, 2002) and can be
used for fungi where mycelial growth is an effective predictor of spore number. In reality, fitness of filamentous
fungi has been measured in a number of different ways
reflecting the complexities associated with their life cycle
of alternating diploid and haploid generations and the
confusion over what constitutes an individual. Also, the
concept of fitness has been used in a wide variety of
ways, which are often not consistent with its usage in
population biology (Antonovics & Alexander, 1986).
Traits such as reproductive rate, infection efficiency and
aggressiveness have been used to describe the fitness of
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
plant pathogenic fungi (Leach et al., 2001). Often one
key spore form such as urediniospore of rusts has been
used to determine the fitness, despite the different sexual
and asexual spores having specific purpose in the overall
life cycle. Consequently, such fitness measures have
limited usefulness in understanding evolutionary and
other mechanisms.
The mode of nutrition plays a significant role in plant
pathogen fitness. For biotrophic pathogens that derive
nutrition only from living host tissue and do not have an
active existence outside of their hosts, fitness can be
determined from fecundity or the heritable latent period,
which is a major component of parasitic fitness (Lehman
& Shaner, 1996). In contrast, necrotrophic fungal pathogens derive nutrition by killing host tissue during infection and also establish, compete, survive and reproduce
on dead organic matter to persist in the absence of living
hosts. Their fitness comprises a pathogenic and a saprophytic component. Saprophytic fitness is essential to
FEMS Microbiol Ecol 81 (2012) 596–609
Fitness of Fusarium pathogens of wheat
necrotrophic pathogens, and when host colonization is
minimized by a resistant host, this allows the population
to grow and reproduce after the host plant dies (Melloy
et al., 2010). The same trait/gene can control pathogenic
and saprophytic fitness in some fungal pathogens, such as
Bipolaris maydis race T (Klittich & Bronson, 1986), but
not in others such as Alternaria alternata (Hatta et al.,
2002).
The necrotrophic Fusarium graminearum (Fg), Fusarium
pseudograminearum (Fp), Fusarium culmorum (Fc) and
other species are economically significant pathogens in
most cereal-growing regions of the world. They infect
the stem base of wheat and barley causing necrosis and
dry rot of the crown, basal stem and root tissue commonly known as crown rot (CR, Backhouse et al., 2004).
The same species also infect floral tissue causing blighting
of the spikelet and developing grains to cause Fusarium
head blight (FHB) or scab in both wheat and barley
(Boutigny et al., 2011). Wet and warm weather during
crop anthesis and maturation may favour FHB (McMullen
et al., 1997), and hot and dry conditions promote CR
(Burgess et al., 2001). Fg is the most prevalent among
FHB pathogens globally (Xu & Nicholson, 2009) including in Australia (Burgess et al., 1987), whereas Fp and Fc
are the predominant CR pathogens (Burgess et al., 2001;
Backhouse et al., 2004; Chakraborty et al., 2006). FHB
has affected vast areas of the globe with recent epidemics
in Canada, China, Europe, South America and the USA
(Goswami & Kistler, 2004). CR is a chronic disease of
economic concern to Australia (Chakraborty et al.,
2006), North America (Dyer et al., 2009), Europe, South
America, West Asia and North Africa (Burgess et al.,
2001). Both diseases curtail grain yield and quality, and
during 1998–2000, an estimated US$2.7 billion was lost
to FHB in the northern Great Plains and central USA as
a result of reduced yield and price discounts from lowered grain quality. One important element of reduced
quality is the production of trichothecenes nivalenol
(NIV), deoxynivalenol (DON) and other mycotoxins in
infected tissue that make them unsafe for human and
animal consumption (Desjardins, 2006).
Studies have revealed clear difference in population
genetics of the three Fusarium species (Miedaner et al.,
2008). The random mating homothallic Fg (teleomorph
Gibberella zeae) is driven by occasional outcrossing, high
gene flow, low host-mediated directional selection and
strong lineages along geographically separated lines. The
heterothallic Fp (teleomorph Gibberella coronicola) is a
single phylogenetic species with limited lineage development (Scott & Chakraborty, 2006), while the anamorphic
Fc shows no obvious clonal structure (Obanor et al.,
2010). All three species can cause CR and FHB under
natural field conditions (Burgess et al., 1987; Bateman,
FEMS Microbiol Ecol 81 (2012) 596–609
597
2005) and in pathogenicity assays (Akinsanmi et al.,
2004).
The three species and their strains differ in overall
DON production, and Fg strains generally produce higher
levels of DON than the other two (Chakraborty et al.,
2006). DON is produced during both FHB (Bai et al.,
2002) and CR (Mudge et al., 2006) infections. Studies
using DON-nonproducing Fg mutants or strains that differ in DON levels have shown that DON production significantly correlated with FHB severity in some studies
(Bai et al., 2002; Goswami & Kistler, 2005) but not in
others (Gale, 2003). Similar studies on CR have shown
reduced stem colonization by Fg and delayed defence
gene expression (Desmond et al., 2008), but there was no
overall difference in CR severity when two wild-type
strains were compared with two DON-nonproducing
strains (Wang et al., 2006).
DON production by Fc and Fg also offers competitive
advantage during saprophytic phase of their life cycle, for
instance, by suppressing the expression of chitinase genes
in Trichoderma atroviride, which is a common antagonist
of many fungi (Lutz et al., 2003). Competition among
Fusarium species is important during the saprophytic
phase but whether DON production offers any advantage
is largely unknown. Species such as Fg with a low saprophytic fitness is rapidly replaced by other competitors
including Fusarium equiseti and Fusarium oxysporum
(Pereyra et al., 2004).
In Australia, FHB is sporadic and limited to south-eastern Queensland and northern New South Wales (Burgess
et al., 1987), but CR is widespread throughout the wheat
belt (Murray & Brennan, 2009). Despite this, FHB poses
a greater risk than CR to food and feed safety from
DON-contaminated grains. Both Fg and Fp caused the
2010 FHB epidemics in eastern Australia, but DON levels
of immature grains were significantly higher when spikes
were infected with Fg than with Fp (Obanor et al., 2012).
The linked aetiology, pathogen biology and epidemiology
of the two diseases in Australia point to a CR-FHB continuum where macroconidia produced on stubbles from
CR infection become FHB inoculum (Mitter et al.,
2006a) under suitable weather conditions. The three
dominant Fusarium species that drive this continuum
have different ecological adaptation, pathogenicity, toxigenicity and possibly saprophytic ability. Improved understanding of biology of these three species can be used to
predict their relative prevalence in response to farming
and weather conditions to improve the management of
FHB epidemics and mycotoxin contamination of grains.
To achieve this overall goal, this study compares the fitness of Fg, Fp and Fc and explores the relationships
between components of pathogenic and saprophytic fitness.
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
598
B. Tunali et al.
Materials and methods
Inoculum preparation
Thirty monoconidial isolates comprising 10 Fg, 13 Fp and
seven Fc collected from eastern Australia were used in
this study (Table 1). Isolates originating from barley or
wheat tissues and identified using both molecular and
morphological techniques were selected to represent a
range of FHB and CR aggressiveness (Akinsanmi et al.,
2004). Data on CR aggressiveness were from 56-day-old
seedlings. Isolates were recovered from storage in 15%
glycerol at 80 °C, and macroconidia suspensions were
obtained by cultivating isolates on quarter-strength potato
dextrose agar (PDA; Difco Laboratories, MD) plates. The
cultures were incubated at room temperature (c. 25 °C)
for 10 days under an alternating 12-h darkness/12-h combined black light (F20T9BL-B20W FL20S.SBL-B NIS,
Japan) and standard cool white fluorescent light (35098
F18E/33 General Electric). Macroconidia were harvested
by flooding individual cultures with 5 mL sterile distilled
Table 1. Source of Fusarium isolates used in this study
Isolate
Species
Host
Plant part
CS3716
CS4494
CS4495
CS4496
CS4497
CS4498
CS4501
CS3005
CS3179
CS3187
CS3192
CS3196
CS3200
CS3259
CS3375
CS3386
CS3407
CS3096
CS3173
CS3175
CS3181
CS3220
CS3270
CS3321
CS3342
CS3350
CS3361
CS3427
CS3438
CS3442
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
F.
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Barley
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Barley
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Wheat
Crown
Crown
Crown
Crown
Crown
Crown
Crown
Spike
Spike
Spike
Spike
Stubble
Spike
Spike
Spike
Stubble
Flag leaf node
Crown
Crown
Spike
Crown
Spike
Crown
Crown
Crown
Crown
Crown
Crown
Crown
Crown
culmorum
culmorum
culmorum
culmorum
culmorum
culmorum
culmorum
graminearum
graminearum
graminearum
graminearum
graminearum
graminearum
graminearum
graminearum
graminearum
graminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
pseudograminearum
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
water and gently scraping colony surfaces with a sterile
L-shaped glass rod. The resulting suspension was filtered
through two layers of sterile cheese cloth to remove mycelia and concentration adjusted using a haemocytometer
(Weber Scientific International, UK) to 105 macroconidia
mL 1 for FHB inoculation and 106 macroconidia mL 1
for CR inoculation. Inoculum was stored at 20 °C until
required.
Aggressiveness and DON production from
Crown rot
Wheat plants of the susceptible durum cultivar ‘Tamaroi’
were grown in a naturally illuminated glasshouse with a
daytime temperature of 25 °C (±5 °C) with 60% (±10%)
relative humidity (RH) and a night-time temperature of
15 °C (±5 °C) with 80% (±10%) RH. For each of the 30
Fusarium isolates (Table 1), six replicate seedlings were
individually raised in sterile potting mix in
5 9 5 9 5 cm punnets housed in seedling trays (Garden
City Plastics, Qld, Australia). Ten days after emergence,
seedlings were laid horizontally on their side, and a 10-lL
droplet of inoculum was applied to the base of the stem
about 5 mm from the soil surface as described previously
(Mitter et al., 2006b). Inoculated seedlings were incubated at high RH in darkness for 48 h after which they
were placed upright in seedling trays. Five weeks after
inoculation, three replicate plants per isolate were
destructively sampled to assess the CR severity of seedlings, while the remaining plants were re-potted in 250mL square pots (Garden City Plastics) and grown to
maturity. The experiment was repeated once.
CR severities on both seedling and adult plants were
used as measures of pathogen aggressiveness. The length
of necrotic discoloration and seedling height were
recorded to express seedling CR severity as the proportion of stem length browning. The proportion of tiller
length browning for each yielding tiller was similarly used
as a measure of CR severity of adult plants. For each replicate plant, DON was determined from grains and a
sample of stem base tissue, covering 10 cm length from
the crown.
Aggressiveness and DON production from FHB
Tamaroi plants were grown in the glasshouse as described
for CR. Five seeds were sown per pot (13 cm
square 9 15 cm) in sterile potting mix (50% sand and
50% peat), and three replicate pots were used for each
isolate. All spikes at mid-anthesis were inoculated by
placing a 10-lL droplet of spore suspension inside the
middle spikelet using a pipette (Akinsanmi et al., 2006).
Control spikes were inoculated with sterile distilled water.
FEMS Microbiol Ecol 81 (2012) 596–609
599
Fitness of Fusarium pathogens of wheat
Inoculated spikes were covered with a moistened sealable
plastic bag to maintain high RH. After 48 h, the plastic
bag was removed and replaced with a paper bag until disease and other assessments. The experiment was repeated
once.
FHB severity at 2 weeks after inoculation was used as a
measure of pathogen aggressiveness. FHB severity was calculated from the proportion of spikelets infected by
recording the number of discoloured and bleached spikelets and the total number of spikelets for each inoculated
spike. Spikes were again covered with paper bags and left
to mature and senesce. At grain maturity, spikes from all
tillers from each plant were harvested and pooled. These
pooled samples were used for mycotoxin extraction and
analysis.
DON measurements
DON content of grain and stem base was determined
using the method of Mirocha et al. (1998) with modifications. DON was extracted in 86% acetonitrile (SigmaAldrich, MO) in water from 1 to 3 g of ground grain or
stem base tissue using an Accelerated Solvent Extraction
(ASE 2000; DIONEX Corporation, CA) equipment. The
extraction protocol had three cycles, each consisting of
heating for 5 min at 40 °C under 10.3-Mpa, 5-min static
phase and a flush phase. Acetonitrile was evaporated
under N in a fume hood and DON resuspended in milliQ water before DON assay. A 96-well competitive
ELISA kit (Beacon Analytical Systems Inc, Portland, ME)
was used following manufacturer’s instructions, and
DON content was estimated from absorbance at 450 nm
using a spectrophotometer (iEMS reader MF; Labsystems, Franklin, MA). When DON content of samples
was beyond the ELISA kit detection range of 0.2 and
5 mg kg 1, extracts were concentrated by evaporating or
diluted with milliQ water.
DON production from saprophytic colonization
of substrates
The level of DON production after saprophytic colonization of cereals by the 30 Fusarium isolates was tested
using sterilized cracked corn, wheat grain and wheat
straw as a substrate. All substrates were soaked in water
overnight and autoclaved for three successive days.
Approximately 350 g of cracked corn or wheat grain, or
55 g of wheat straw dispensed into 15-cm-diameter Petri
dishes was used as a replicate. Three replicates per isolate
were inoculated with a droplet of 106 macroconidia mL 1
and incubated at 25 °C for 21 days with weekly shaking
to break up mycelial matting. The colonized substrates
were dried in a laminar flow, ground in a coffee grinder
and stored at 4 °C until used. The extraction and determination of DON from ground samples followed the
methods described above. The experiment was repeated
once.
Rate of saprophytic colonization of wheat
straw
The rate of saprophytic colonization of wheat straw by
the 30 isolates at 15 and 25 °C was determined using a
recently described technique (Melloy et al., 2010). Disease-free wheat straw cut into 8-cm pieces was soaked in
water for 24 h and autoclaved for three successive days.
Three replicate straws were inoculated for each isolate by
pressing one end onto an actively growing culture; each
inoculated straw was placed in a Petri dish, sealed with
parafilm and incubated at either 15 or 25 °C for 4 days.
After incubation, each straw was cut into eight pieces,
each one cm long, and plated on fresh PDA plates. Based
on the number of pieces yielding Fusarium colonies, saprophytic fitness was expressed as the total length of straw
colonized by an isolate. The experiment was repeated
once.
Mycelial growth rate and fecundity on PDA
Mycelial growth on 9-cm-diameter Petri plate and fecundity were studied using full-strength PDA at 25 °C.
Three replicate cultures for each of the 30 isolates were
initiated by inoculating a 4-mm-diameter core taken
from the edge of an actively growing culture on quarterstrength PDA. Colony diameter was measured at 2, 4
and 6 days after inoculation. Macroconidia were harvested from 6-day-old cultures to prepare a suspension
following methods used to make inoculum. Spore concentration was determined using a haemocytometer, and
fecundity was expressed as the number of conidia per
unit area of the culture. The experiment was repeated
once.
FEMS Microbiol Ecol 81 (2012) 596–609
Data analysis
The influence of Fusarium species, repeat run of the
experiment and isolates on each fitness measure was analysed using analysis of variance. Isolate was nested within
species using the general linear models procedure in SAS
(PROC GLM, SAS Institute Inc., Cary, NC). Data were
transformed, as necessary to stabilize variance.
A total of 13 fitness measures were available for analysis:
six describing pathogenic fitness were: (i) FHB aggressiveness, (ii) CR aggressiveness on seedlings (ACR-S), (iii) CR
aggressiveness on adult plants (ACR-A), (iv) DON in
grain from FHB, (v) DON in grain from CR, and (vi)
DON in stem base from CR. Seven describing saprophytic
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
600
fitness were: (i) DON in wheat straw from saprophytic
growth, (ii) DON in wheat grain from saprophytic growth,
(iii) DON in cracked corn from saprophytic growth, (iv)
growth rate on media, (v) fecundity on media, (vi) saprophytic wheat straw colonization at 15 C and (vii) saprophytic wheat straw colonization at 25 C. Correlation and
principal component analysis (PCA) were used to explore
how the 13 measures explained the overall fitness of the
30 Fusarium isolates. Isolates were ranked for each of the
13 fitness measures to generate a data matrix of 13 variates
(fitness measures) and 30 observations (isolates), and
principal components were calculated using the PRINCOMP
procedure in SAS.
Two-dimensional scatter plots, also known as biplots,
were generated by transposing data to produce a matrix
of 13 observations (fitness measures) and 30 variates (isolates). The transposed data were monotonically transformed using PRINQUAL procedure with the MDPREF
option to maximize the proportion of variance accounted
for by the first two principal components. The FACTOR
procedure was used on the transformed data to perform
a PCA, and the biplot was created using the %PLOTIT
macro available as part of the SAS autocall library.
Results
Aggressiveness and DON production from
Crown rot
Data on ACR-S and DON in grains were arcsinetransformed, DON in stem base was log-transformed to
B. Tunali et al.
stabilize variance, and CR aggressiveness on mature plants
was analysed untransformed. Although all main effect and
their interactions were significant (P < 0.05) for seedling
severity (output of analysis not shown), the level of aggressiveness measured as the proportion of stem length browning was generally low with relatively small difference
between species (Fig. 1). ACR-S for individual isolates ranged from 0.15 to 0.4 for Fc, 0.05 to 0.31 for Fg and 0.02 to
0.48 for Fp. For ACR-A, analysis showed a significant
(P < 0.05) effect of species and isolate only. The overall difference between aggressiveness of the three species was
more pronounced in adult plants than in seedlings, and Fp
was significantly more aggressive than the other two species, while Fc was significantly more aggressive than Fg
(output of analysis not shown). The range for adult plant
aggressiveness was also wider than for seedlings for all three
species: 0.12 to 0.63 for Fc, 0.02 to 0.28 for Fg and 0.07 to
0.93 for Fp. One Fc and six Fp isolates showed high level of
aggressiveness causing > 50% tiller length browning of
adult plants, but none of the Fg isolates had such high level
of aggressiveness (Fig. 2). While 85% of Fp isolates were
more aggressive on adult plants than on seedlings, this
compared with 40% of Fg and 71% of Fc isolates. These
data show that Fp has higher pathogenic fitness for CR than
the other two species.
With an overall mean of 7.43 mg kg 1, all three Fusarium
species produced high levels of DON in the stem base
tissue of CR-infected plants (Fig. 3). Only Fusarium
species and isolate had significant effect on stem base
DON (output of analysis not shown), and both Fg
(8.51 mg kg 1) and Fp (8.49 mg kg 1) produced similar
Fig. 1. FHB and CR aggressiveness of Fusarium culmorum, Fusarium graminearum and Fusarium pseudograminearum on seedling and adult
plants of wheat. The bar represents standard error of the mean. CR aggressiveness was measured as the proportion of stem length browning
5 weeks after inoculation for seedlings and at maturity for adult plants. FHB aggressiveness was measured as the proportion of spikelets infected
2 weeks after inoculation.
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
FEMS Microbiol Ecol 81 (2012) 596–609
Fitness of Fusarium pathogens of wheat
601
Fig. 2. FHB and CR aggressiveness of individual isolates of Fusarium culmorum, Fusarium graminearum and Fusarium pseudograminearum on
seedling and adult plants of wheat. The bar represents standard error of the mean. See Fig. 1 for description of CR and FHB aggressiveness.
high levels, while Fc (4.13 mg kg 1) produced significantly less. In contrast, very little DON was found in
grains of CR-affected plants, and despite a significant isolate effect, DON levels were generally low (overall mean
0.36 mg kg 1), and there was very little difference
between the three Fusarium species (output of analysis not
shown). Of the 30 isolates, only three Fc (CS4495, CS4496
and CS4501) and one Fp (CS3427) had > 1 mg kg 1
FEMS Microbiol Ecol 81 (2012) 596–609
DON in grains from CR infection, but DON levels in stem
base tissue were > 100-fold higher for some isolates
(Fig. 4). Of the 30 isolates, 6/10 Fg, 8/13 Fp and 1/7 Fc
produced > 5 mg kg 1 DON in stem base tissue.
ACR-A significantly correlated with DON in stem base
(DCR-S, r = 0.41, P < 0.01) and ACR-S according to
Pearson’s correlation coefficient (Table 2). When data for
each species were considered separately, the correlation
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
602
B. Tunali et al.
Fig. 3. DON content of wheat grain and stem base following FHB or CR disease caused by Fusarium culmorum, Fusarium graminearum or
Fusarium pseudograminearum. Bar represents standard error of the mean.
coefficient (r = 0.68, data not shown) for Fp was highly
significant (P < 0.001), indicating that DCR-S is an essential component of its CR pathogenic fitness, although the
highly aggressive CS3342 was a low DON producer. In
contrast, four isolates of Fg (CS3005, CS3196, CS3200
and CS3407) with low ACR-S and ACR-A produced
> 10 mg kg 1 DCR-S (Figs 2 and 4), and Pearson’s correlation coefficient (r = 0.45) from a species-wise analysis
was nonsignificant for this species.
Aggressiveness and DON production from FHB
FHB aggressiveness data were square-root-transformed,
and DON in grain was log-transformed for an analysis of
variance. Fusarium species and isolates differed significantly (P < 0.05) in FHB aggressiveness (output of analysis not shown), and Fc was significantly more aggressive
than the other two species that were equally aggressive
(Fig. 1). There were aggressive isolates in each Fusarium
species. Eleven highly aggressive isolates, three Fg, three
Fp and five Fc, infected > 20% spikelets (Fig. 2). Of
these, only two Fg (CS3005 and CS3187) and one Fp
(CS3220) originated from spike tissue (Table 1), and all
remaining isolates were obtained from crown tissue or
wheat stubble. This clearly demonstrates the inherent
ability of Fusarium species and isolates commonly
associated with CR to cause severe FHB under suitable
conditions.
Both Fusarium species and isolates significantly influenced DON production in grains from FHB infection
(DHB-G) (output of analysis not shown). As a FHB
pathogen, Fp produced significantly less DHB-G compared with the other two species, which produced similar DON levels (Fig. 3). However, as a FHB pathogen,
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
Fg is more toxigenic than Fc. Of the seven Fg isolates
with > 1 mg kg 1 DHB-G, four produced between 2
and 13 mg kg 1, but the high level of DON production
by Fc was because of a single isolate (CS3716) producing > 25 mg kg 1 (Fig. 4). The highest DHB-G by any
Fp isolate was 2.4 mg kg 1. When data for all three
species were considered, DHB-G significantly (P < 0.01)
correlated (r = 0.5) with FHB aggressiveness (AHB,
Table 2). From a species-wise analysis, the correlation
coefficient (r = 0.71, data not shown) was significant
(P < 0.001) for Fg, but nonsignificant for Fc (r = 0.48,
P < 0.08) or Fp (r = 27, P = 0.19). Given the similar
levels of AHB for Fg and Fp, DHB-G production
appears to be only one of many aspects of FHB pathogenic fitness.
Components of saprophytic fitness
Data on mycelial growth rate per day were arcsine-transformed, and fecundity was square-root-transformed to
stabilize variance. The influence of Fusarium species,
repeat run of the experiment and isolate was analysed
using analysis of variance with isolate nested within species. All three species had similar growth rates on PDA at
25 °C (data not shown), but conidia production on PDA
was significantly different for the three species and isolates within each species. With 0.9 9 104 macroconidia
per unit colony area, Fp had the lowest fecundity and this
was significantly less than fecundity of the other two species (Fc 5.3 9 104 and Fg 8.2 9 104). However, there was
significant difference in fecundity among isolates within
each species, and there was a large variation between replicates and the two times the experiment was run (data
not shown).
FEMS Microbiol Ecol 81 (2012) 596–609
Fitness of Fusarium pathogens of wheat
603
Fig. 4. DON content of wheat grain and stem base following FHB or CR disease caused by isolates of Fusarium culmorum, Fusarium
graminearum or Fusarium pseudograminearum. Bar represents standard error of the mean.
Data on DON production from saprophytic colonization of wheat straw (DWS), wheat grain (DWG) and
cracked corn (DCG) as substrates were log-transformed
before an analysis of variance to examine the effect of
Fusarium species and isolates on DON levels. There was
no significant difference between species, but both isolate
and substrate were significant (P < 0.05). Significantly
higher amount of DON was produced on wheat straw
(0.19 mg kg 1), and this was followed by cracked corn
(0.12 mg kg 1) and wheat grains (0.03 mg kg 1), but the
species 9 substrate interaction was also significant
(P < 0.05). However, the overall low level of DON production ranging from 0.03 to 0.3 mg kg 1 (data not
shown) makes it difficult to pinpoint any obvious
FEMS Microbiol Ecol 81 (2012) 596–609
substrate-isolate/species combination with the potential to
produce high levels of DON, and any trend has to be
interpreted with caution.
An analysis of variance of square-root-transformed data
on the rate of saprophytic colonization of wheat straw at
15 (SG-15) and 25 °C (SG-25) showed significant
(P < 0.05) effect of Fusarium species, isolate, temperature
and interactions with temperature (output of analysis not
shown). Despite the significant species 9 temperature
interaction, all three species had a higher SG-25 than
SG-15 (Fig. 5). At the species level, the rate of straw colonization accelerated at a rapid rate in both Fc and Fp as
temperature increased from 15 to 25 °C but the rate of
acceleration was lower in Fg (Fig. 5).
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
604
B. Tunali et al.
Table 2. Pearson’s correlation coefficients (r) between measures of pathogenic fitness head blight aggressiveness (AHB), ACR-S, ACR-A, DON in
grain from FHB (DHB-G), DON in grain from CR (DCR-G), DON in stem base from CR (DCR-S); and saprophytic fitness DON in wheat straw from
saprophytic growth (DWS), DON in wheat grain from saprophytic growth (DWG), DON in cracked corn from saprophytic growth (DCG),
fecundity on media (FEC), saprophytic wheat straw colonization at 15 °C (SG-15) and saprophytic wheat straw colonization at 25 °C (SG-25) for
30 isolates from three Fusarium species. Probability > |r| under H0: ρ = 0 is indicated with *for P < 0.05 and ** for P < 0.01
Pathogenic fitness
ACR-S
AHB
ACR-S
ACR-A
DHB-G
DCR-G
DCR-S
DWS
DWG
DCG
FEC
SG-15
0.07
ACR-A
0.1
0.4**
DHB-G
0.5 **
0.09
0.15
DCR-G
0.13
0.03
0.02
0.04
DCR-S
0.02
0.2
0.41**
0.1
0.1
Overall fitness of Fusarium isolates
There were three significant (P < 0.05) correlations
between the six measures of pathogenic fitness, FHB
aggressiveness (AHB), ACR-S, ACR-A, DON in grain
from FHB (DHB-G), DON in grain from CR (DCR-G)
and DON in stem base from CR (DCR-S) (Table 2),
showing obvious links between DON production and
aggressiveness. There was also the same number of significant correlations between the seven measures of saprophytic fitness, DON in wheat straw from saprophytic
growth (DWS), DON in wheat grain from saprophytic
growth (DWG), DON in cracked corn from saprophytic
growth (DCG), growth rate on media (no significant correlation with any variable and not shown in Table 2),
fecundity on media (FEC), saprophytic wheat straw colonization at 15 °C (SG-15) and saprophytic wheat straw
colonization at 25 °C (CS-25); two of these were linked
to SG-25. More importantly for this necrotrophic pathogen, there were four significant correlations between components of pathogenic and saprophytic fitness, including
between DWG and DWS with AHB, DHB-G and DCR-G.
SG-25 was also significantly correlated with ACR-A.
The first seven principal components explained > 86%
of the variance in a PCA, with each additional component explaining < 5%, indicating that variation in fitness
of the 30 isolates has seven major dimensions (output of
analysis not shown). Eigenvector of the first component
explained 18% of the variation with large (> 25%) positive weight on three Fg and one Fp and a large negative
weight on one Fp isolate (data not shown). The second
eigenvector explained a further 16% of variation with
positive weights for one Fc, three Fg and one Fp isolates.
The two-dimensional scatter plot (Fig. 6) revealed a
grouping of the DON production–related measures DCG,
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
Saprophytic fitness
DWS
DWG
0.05
0.09
0.04
0.32*
0.14
0.01
0.27*
0.05
0.07
0.04
0.37**
0.9
0.7
DCG
0.1
0.1
0.2
0.2
0.01
0.1
0.08
0.07
FEC
0.25
0.06
0.2
0.06
0.2
0.1
0.1
0.32*
0.1
SG-15
0.0
0.18
0.1
0.2
0.1
0.1
0.04
0.07
0.2
0.2
SG-25
0.05
0.06
0.36**
0.2
0.2
0.1
0.03
0.8
0.3*
0.03
0.26*
DCR-G, DHB-G, DWG, together with AHB and saprophytic growth on media along vectors of isolates with
high AHB (e.g. CS3187, CS4495, CS4501) or low ACR-A
and ACR-S (e.g. CS3220, CS3259, CS3350). But the fitness of 6 (CS3005, CS3200, CS3196, CS3716, CS4496 and
CS 3173) of 10 isolates with high AHB could not be
explained using the 13 measures used. While DCR-S was
aligned with vectors of isolates with high ACR-A and
ACR-S (e.g. CS3321, CS3270, CS3342), it did not group
with ACR-S or ACR-A, which together with DWS were
located along vectors of other isolates with moderate (e.g.
CS3181, CS4498) to high (e.g. CS3096, CS3361, CS3442)
ACR-A and ACR-S. This suggests that DON production
in stem base may be only one of the factors essential for
high CR aggressiveness. SG-15, located far left of origin
of isolate vectors, did not contribute to the discrimination of isolates. The vector for Fc CS4496 did not align
with any of the 13 fitness measures used. Why this low
DON-producing isolate originating from wheat crown
with moderate CR and high FHB aggressiveness that is
generally similar to some other isolates (e.g. CS3173,
CS3220) does not group with any other isolate needs further study.
Discussion
This work has for the first time compared important elements of saprophytic and pathogenic fitness controlling
FHB and CR aggressiveness of three important Fusarium
pathogens of wheat and barley. Results show that these
necrotrophic species differ in their overall fitness as
pathogens of both diseases. Pathogenic fitness was generally linked to DON production in infected tissue. The
superior fitness of Fp as a CR pathogen was linked to
high DON production in the stem base tissue, while Fc
FEMS Microbiol Ecol 81 (2012) 596–609
Fitness of Fusarium pathogens of wheat
(a)
(b)
(c)
Fig. 5. The daily rate of colonization of wheat straw incubated at 15
and 25 °C by seven Fusarium culmorum (a), 10 Fusarium
graminearum (b) and 14 Fusarium pseudograminearum (c) isolates.
The solid line in each panel shows the mean daily rate for each
species, and the bar represents the standard error of the mean.
and Fg had superior FHB fitness with high DON production in grains. While some isolates of all three species
have similar CR or FHB aggressiveness, they have different toxigenicity and do not produce the same level of
DON in infected tissue. There is a significant correlation
FEMS Microbiol Ecol 81 (2012) 596–609
605
between some saprophytic and pathogenic fitness components such as saprophytic DON production in sterile
grain and straw with FHB aggressiveness or DON production in infected grain, and between the rates of saprophytic colonization of straw at 25 °C with ACR-A.
Overall, Fp had superior fitness as a CR pathogen
with the majority of isolates causing severe CR of adult
plants. Our findings on the superiority of Fp over Fc
and Fg as a CR pathogen of mature plants are in line
with published literature (Backhouse et al., 2004; Chakraborty et al., 2006; Dyer et al., 2009). Although there
was a significant correlation between CR severity of
seedling and adult plants, all three Fusarium species
had largely similar ACR-S and the relatively small difference in aggressiveness between the species magnified
on mature plants. Severity of adult plants is a more
meaningful measure because of its practical relevance to
CR resistance in the field. Most of the highly aggressive
Fp isolates produced high levels of DON in the infected
stem base tissue of adult plants. Although DON production in straw by Fusarium species has been reported
earlier (e.g. Brinkmeyer et al., 2006), this is the first
report linking CR aggressiveness of Fp to DON production in straw. Some Fc isolates (CS4495 and CS4497)
with high ACR-A did not produce high levels of DON
in the stem base. At the species level, ACR-A was significantly higher for Fp isolates than for Fg, although
there was no significant difference between these species
in DON production in the stem base. This suggests
more than one pathogenicity mechanisms operating in
the two species.
As a species, Fc was significantly more aggressive than
the other two species for FHB, but as with CR, some isolates within each species were equally aggressive. This is
somewhat surprising because the environmental conditions used in these studies for plant growth and infections
were warmer than in the natural range for Fc (Backhouse
et al., 2004). Also, in common with the other two species,
Fc was a faster saprophytic colonizer of straw at 25 °C
than at 15 °C. Both Fc and Fp accelerated saprophytic
colonization of straw faster than Fg when temperature
was increased from 15 to 25 °C. However, despite being
an important FHB pathogen in Europe (Bateman, 2005)
and Australian isolates being capable of causing FHB
in pathogenicity assays (Akinsanmi et al., 2004), a
Fc-induced FHB epidemic has never been reported in
Australia. It remains to be seen if this species will pose a
FHB risk for Australia under suitable weather and farming conditions.
Overall, there was a significant correlation between
DHB-G and AHB, indicating an important role of DON
as a component of pathogenic fitness. However, at the
species level, the correlation was significant for Fg and Fc,
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
606
B. Tunali et al.
Fig. 6. Two-dimensional scatter plot to show the association between 30 isolates of Fusarium culmorum (Fc), Fusarium graminearum (Fg) and
Fusarium pseudograminearum (Fp) and 13 fitness measures, head blight (FHB) aggressiveness (AHB), ACR-S, ACR-A, DON in grain from FHB
(DHB-G), DON in grain from CR (DCR-G), DON in stem base from CR (DCR-S), DON in wheat straw from saprophytic growth (DWS), DON in
wheat grain from saprophytic growth (DWG), DON in cracked corn from saprophytic growth (DCG), growth rate on agar media (GRO), fecundity
on media (FEC), saprophytic wheat straw colonization at 15 °C (SG-15) and saprophytic wheat straw colonization at 25 °C (SG-25). The data
matrix of fitness measures and isolates was monotonically transformed; principal components were analysed using the FACTOR procedure and
plotted using the %PLOTIT macro from the SAS autocall library. The direction of isolate vectors indicates the most favoured association with the
13 fitness measures (open circles) based on coefficients for the first two principal components.
but not for Fp, supporting previous findings that the role
of trichothecenes in FHB pathogenesis differs among species (Langevin et al., 2004). For Fg, DON production
enhanced FHB aggressiveness in some studies (Bai et al.,
2002) but not in others (Gale, 2003), while DON production by Fc isolates has been implicated in pathogenesis
(Muthomi et al., 2000). However, data on DON from
small samples of grains need to be treated with caution
because of inherent variability among grains from the
same plant/spike. DON levels need to be confirmed from
large samples of bulked grains.
Our findings are similar to published research
(Akinsanmi et al., 2004) which showed that a small group
of Fp, Fg and Fc isolates have high aggressiveness for both
CR and FHB. In this study, Fc CS4495 and CS4497; Fg
CS3375 and CS3407; and Fp CS3173 and CS3361 had
moderate to high aggressiveness for both CR and FHB.
However, there was no overall link between FHB and CR
aggressiveness, and the correlation coefficient was not significant for any species. Recent studies on pathogenesis
mechanisms have highlighted differences between the two
diseases. Similarities during early stages of pathogenesis
for the two diseases were replaced with distinct phases of
colonization during later stages of CR infection, and each
phase was associated with a different fungal gene expression profile (Stephens et al., 2008).
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
This study has clearly established Fp as the least toxigenic of the three Fusarium species. As a FHB pathogen,
Fp produced just over 1 mg kg 1 DON in grains, while
the other two species each produced well over 3 mg kg 1,
although for Fc, this was because of a single isolate
CS3716 producing over 25 mg kg 1. Difference in DON
production in Australian Fg and Fp isolates has been
reported before (Blaney & Dodman, 2002). In common
with published literature (Mudge et al., 2006), we have
detected DON in grains as a result of CR infection by all
three Fusarium species, but levels are very low with only
one Fp isolate CS3427 producing 1.8 mg kg 1. This is
consistent with negligible levels of DON in Australian
wheat where CR caused by the widely distributed Fp is a
chronic disease in much of this moisture-limiting environment (Backhouse et al., 2004; Chakraborty et al.,
2006). Although both Fp and Fg have caused FHB epidemics in Australia (Burgess et al., 1987; Southwell et al.,
2003), our findings show that FHB epidemics caused by
Fp will lead to lower DON in grains compared with epidemics because of Fg or Fc, with obvious grain quality,
food and feed safety implications (Desjardins, 2006).
These findings are confirmed by field data from the latest
Australian FHB epidemics in 2010, where high level of
DON in grains occurred only when Fg was responsible
for FHB symptoms (Obanor et al., 2012). Hence, findings
FEMS Microbiol Ecol 81 (2012) 596–609
607
Fitness of Fusarium pathogens of wheat
from these studies using standardized glasshouse conditions can be used to streamline surveillance and management of DON by targeting areas where FHB epidemics
are caused by Fg or Fc.
The level of DON production in infected tissue generally
increased by several orders of magnitude when compared
with DON production in vitro or from saprophytic colonization of substrates in these studies. This is in common
with previous findings (Mudge et al., 2006; Voigt et al.,
2007). Nevertheless, some isolates can produce high levels
of DON in wheat grains from saprophytic colonization
(Chakraborty et al., 2006). Also, DON level in grains from
CR infection was much lower than DON level in grains
from a direct infection of spike tissue during FHB. Recent
in vitro nutrient profiling studies with Fg have shown that
treatments with a variety of polyamines increased DON
production levels to > 1000 mg kg 1 (Gardiner et al.,
2009). Polyamines are well-known plant metabolites produced in response to abiotic stress including water stress,
but their role in pathogenicity and DON production is not
well understood. Spray inoculation of Fg at mid-anthesis
in an FHB infection assay led to concomitant increases in
polyamines, Fg biomass and DON in spike tissue (Gardiner et al., 2010). These authors suggested that Fusarium
pathogens may have evolved to recognize these metabolites
and this may explain severe CR epidemics in droughtstressed environments. However, the overall low DON levels of Australian wheat indicate that factors in addition to
polyamines influence DON levels.
There is an ecological adaptation among the three
pathogens that further influence their fitness. Macroconidia, not ascospores, are the main inoculum source for
FHB in Australia, and Australian Fg isolates produce
fewer perithecia in culture or in the field compared with
isolates from the USA (Mitter et al., 2006a). With winter
snow covering wheat fields postharvest in the USA, the
production of perithecia on crop residues is critical to
pathogen survival. These perithecia release massive quantities of ascospores in spring and summer to cause FHB
(De Luna et al., 2002). As a spike-infecting inoculum for
FHB, long-distance aerial dispersal of ascospores has a
distinct advantage over short-distance splash-dispersed
macroconidia, and this may be a further reason for the
limited distribution of FHB in Australia. In this study,
isolates with high FHB aggressiveness were obtained from
crown, spike and stubble tissue, suggesting that FHB
infection may be opportunistic. In contrast, all isolates
except Fp CS3175 with high CR aggressiveness originated
from the crown tissue, which may indicate an adaptation
in the Australian Fusarium pathogens towards CR.
The biology and ecological adaptation of the three
Fusarium species in Australia (Chakraborty et al., 2006;
Miedaner et al., 2008) also prompted us to consider
FEMS Microbiol Ecol 81 (2012) 596–609
fitness traits associated with only the vegetative part of
their life cycle. While Fc does not have a known sexual
stage, in Australia, the sexual stage is infrequent to rare
for the other two species. However, a comprehensive
understanding of fitness of these important Fusarium species will require studying large number of isolates from
around the globe.
This study shows that both pathogenic fitness and saprophytic fitness contribute to the overall fitness of these
necrotrophic pathogens, although only a limited number
of components were assessed. Saprophytic growth on
media and DON production from saprophytic colonization of straw and grain were linked to high FHB aggressiveness. Similarly, the high rate of saprophytic
colonization of wheat straw by Fp correlated with its high
ACR-A. However, these findings from sterile wheat straw
do not represent true competitive saprophytic ability in
the field. Field studies in the USA have shown that Fg is
a weak saprophyte and is rapidly replaced from colonized
straw by other organisms including other Fusarium species (Pereyra et al., 2004), while Fc may persist as chlamydospores in soil. Studies using isolates with different
toxigenic potential from each Fusarium species are needed
to better assess their competitive saprophytic fitness on
crop residues, including any potential role of DON and
how this may be linked to their pathogenic fitness. Saprophytic fitness is essential in pathogen life cycle to enable
the population to bounce back when partially resistant
host varieties restrict their pathogenic growth and reproduction (Melloy et al., 2010). Existing crop residue management tools such as crop rotation is widely used to
reduce CR and FHB inoculum. Improved knowledge of
overall fitness of necrotrophic pathogens through further
studies may lead to novel management strategies.
Acknowledgements
The senior author was awarded an Endeavour Research
Fellowship, and G.E. received a Crawford Fund training
award for this research. Funding for this work was provided by the Grains Research and Development Corporation of Australia and CSIRO Plant Industry. Ross Perrott,
Alan Tan and Swati Kothari provided technical assistance.
All assistance is gratefully acknowledged.
References
Akinsanmi OA, Mitter V, Simpfendorfer S, Backhouse D &
Chakraborty S (2004) Identity and pathogenicity of
Fusarium spp. from wheat fields in Queensland and
northern New South Wales. Aust J Agric Res 55: 97–107.
Akinsanmi OA, Backhouse D, Simpfendorfer S & Chakraborty
S (2006) Genetic diversity of Australian Fusarium
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
608
graminearum and F. pseudograminearum. Plant Pathol 55:
494–504.
Antonovics J & Alexander H (1986) The concept of fitness in
plant fungal pathogen systems. Plant Disease Epidemiology,
Vol. 2 (Leonard K & Fry W, eds), pp. 185–214. McGrawHill Publishing Company, New York.
Backhouse D, Abubakar A, Burgess L, Dennis JI, Hollaway GJ,
Wildermuth GB, Wallwork H & Henry FJ (2004) Survey of
Fusarium species associated with crown rot of wheat and
barley in eastern Australia. Australas Plant Pathol 33: 255–
261.
Bai GH, Desjardins AE & Plattner RD (2002) Deoxynivalenolnonproducing Fusarium graminearum causes initial
infection, but does not cause disease spread in wheat spikes.
Mycopathologia 153: 91–98.
Bateman GL (2005) The contribution of ground-level
inoculum of Fusarium culmorum to ear blight of winter
wheat. Plant Pathol 54: 299–307.
Blaney BJ & Dodman RL (2002) Production of Zearalenone,
Deoxynivalenol, Nivalenol, and acetylated derivatives by
Australian isolates of Fusarium graminearum and
F. pseudograminearum in relation to source and culturing
conditions. Aust J Agric Res 53: 1317–1326.
Boutigny A-L, Ward TJ, Van Coller GJ, Flett B, Lamprecht SC,
O’Donnell K & Viljoen A (2011) Analysis of the Fusarium
graminearum species complex from wheat, barley and maize
in South Africa provides evidence of species-specific
differences in host preference. Fungal Genet Biol 48: 914–
920.
Brinkmeyer U, Dänicke S, Lehmann M et al. (2006) Influence
of a Fusarium culmorum inoculation of wheat on the
progression of mycotoxin accumulation, ingredient
concentrations and ruminal in sacco dry matter degradation
of wheat residues. Arch Anim Nutr 60: 141–157.
Burgess LW, Klein TA, Bryden WL & Tobin NF (1987) Head
blight of wheat caused by Fusarium graminearum Group 1
in New South Wales in 1983 [fungal disease; survey].
Australas Plant Pathol 16: 72–78.
Burgess LW, Backhouse D, Summerell BA & Swan LJ (2001)
Crown Rot of Wheat. Fusarium: Paul E. Nelson Memorial
Symposium. (Summerell BA, Leslie JF, Backhouse D,
Bryden WL & Burgess LW, eds), pp. 271–294. APS Press, St.
Paul, MN.
Chakraborty S, Liu CJ, Mitter V, Scott JB, Akinsanmi OA, Ali
S, Dill-Macky R, Nicol JM, Backhouse D & Simpfendorfer S
(2006) Pathogen population structure and epidemiology are
keys to wheat Crown rot and Fusarium head blight
management. Australas Plant Pathol 35: 643–655.
De Luna L, Bujold I, Carisse O & Paulitz TC (2002) Ascospore
gradients of Gibberella zeae from overwintered inoculum in
wheat fields. Can J Plant Pathol 24: 457–464.
Desjardins AE (2006) Fusarium Mycotoxins Chemistry, Genetics
and Biology. The American Phytopathological Society, St.
Paul, MN.
Desmond OJ, Manners JM, Stephens AE, Maclean DJ, Schenk
PM, Gardiner DM, Munn AL & Kazan K (2008) The
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved
B. Tunali et al.
Fusarium mycotoxin deoxynivalenol elicits hydrogen
peroxide production, programmed cell death and defence
responses in wheat. Mol Plant Pathol 9: 435–445.
Dyer AT, Johnston RH, Hogg AC & Johnston JA (2009)
Comparison of pathogenicity of the Fusarium crown rot
(FCR) complex (F-culmorum, F-pseudograminearum and
F-graminearum) on hard red spring and durum wheat. Eur J
Plant Pathol 125: 387–395.
Gale LR (2003) Population Biology of Fusarium species
causing Head Blight of grain crops. Fusarium Head Blight of
Wheat and Barley (Leonard KJ & Bushnell WR, eds), pp.
120–143. APS Press, St. Paul, MN.
Gardiner D, Kazan K & Manners J (2009) Nutrient profiling
reveals potent inducers of trichothecene biosynthesis in
Fusarium graminearum. Fungal Genet Biol 46: 604–613.
Gardiner D, Kazan K, Praud S, Torney F, Rusu A & Manners J
(2010) Early activation of wheat polyamine biosynthesis
during Fusarium head blight implicates putrescine as an
inducer of trichothecene mycotoxin production. BMC Plant
Biol 10: 289.
Goswami RS & Kistler HC (2004) Heading for disaster:
Fusarium graminearum on cereal crops. Mol Plant Pathol 5:
515–525.
Goswami R & Kistler H (2005) Pathogenicity and in planta
mycotoxin accumulation among members of the Fusarium
graminearum species complex on wheat and rice.
Phytopathology 95: 1397–1404.
Hatta R, Ito K, Hosaki Y, Tanaka T, Tanaka A, Yamamoto M,
Akimitsu K & Tsuge T (2002) A conditionally dispensable
chromosome controls host-specific pathogenicity in the
fungal pathogen Alternaria alternata. Genetics 161: 59–70.
Klittich CJR & Bronson CR (1986) Reduced fitness associated
with Tox 1 of Cochliobolus heterostrophus. Phytopathology 76:
1294–1298.
Langevin F, Eudes F & Comeau A (2004) Effect of
Trichothecenes produced by Fusarium graminearum during
Fusarium head blight development in six cereal species. Eur
J Plant Pathol 110: 735–746.
Leach JE, Vera Cruz CM, Bai J & Leung H (2001) Pathogen
fitness penalty as a predictor of durability of disease
resistance genes. Annu Rev Phytopathol 39: 187–224.
Lehman J & Shaner G (1996) Genetic variation in latent period
among isolates of Puccinia recondita f. sp. tritici on partially
resistant wheat cultivars. Phytopathology 86: 633–641.
Lutz M, Feichtinger G, Défago G & Duffy B (2003)
Mycotoxigenic Fusarium and deoxynivalenol production
repress chitinase gene expression in the biocontrol agent
Trichoderma atroviride P1. Appl Environ Microbiol 69: 3077–
3084.
McMullen M, Jones R & Gallenberg D (1997) Scab of wheat
and barley: a re-emerging disease of devastating impact.
Plant Dis 81: 1340–1348.
Melloy P, Hollaway G, Luck J, Norton R, Aitken E &
Chakraborty S (2010) Production and fitness of Fusarium
pseudograminearum inoculum at elevated carbon dioxide in
FACE. Glob Change Biol 16: 3363–3373.
FEMS Microbiol Ecol 81 (2012) 596–609
Fitness of Fusarium pathogens of wheat
Miedaner T, Cumagun C & Chakraborty S (2008) Population
genetics of three important head blight pathogens Fusarium
graminearum, F. pseudograminearum and F. culmorum.
J Phytopathol 156: 129–139.
Mirocha C, Kolaczkowski E, Xie W, Yu H & Jelen H (1998)
Analysis of Deoxynivalenol and its derivatives (batch and
single kernel) using gas chromatography/mass spectrometry.
J Agric Food Chem 46: 1414–1418.
Mitter V, Francl LJ, Ali S, Simpfendorfer S & Chakraborty S
(2006a) Ascosporic and conidial inoculum of Gibberella zeae
play different roles in Fusarium head blight and crown rot
of wheat in Australia and the USA. Australas Plant Pathol
35: 441–452.
Mitter V, Zhang M, Liu C, Ghosh R, Ghosh M & Chakraborty
S (2006b) A high throughput glasshouse bioassay to detect
crown rot resistance in wheat germplasm. Plant Pathol 55:
433–441.
Mudge AM, Dill-Macky R, Dong Y, Gardiner DM, White RG &
Manners JM (2006) A role for the mycotoxin deoxynivalenol
in stem colonisation during crown rot disease of wheat
caused by Fusarium graminearum and Fusarium
pseudograminearum. Physiol Mol Plant Pathol 69: 73–85.
Murray G & Brennan J (2009) Estimating disease losses to the
Australian wheat industry. Australas Plant Pathol 38: 558–
570.
Muthomi JW, Schutze A, Dehne HW, Mutitu EW & Oerke EC
(2000) Characterization of Fusarium culmorum isolates by
mycotoxin production and aggressiveness to winter wheat.
J Plant Dis Prot 107: 113–123.
Obanor F, Erginbaş G, Tunali BA, Nicole J & Chakraborty S
(2010) Fusarium culmorum is a single phylogenetic species
based on multilocus sequence analysis. Fungal Biol 114:
753–765.
FEMS Microbiol Ecol 81 (2012) 596–609
609
Obanor F, Neate S, Simpfendorfer S, Sabburg R, Wilson P &
Chakraborty S (2012) Fusarium graminearum and F.
pseudograminearum caused the 2010 head blight epidemics
in Australia. Plant Pathol DOI: 10.1111/j.1365-3059.
2012.02615.x.
Pereyra SA, Dill-Macky R & Sims AL (2004) Survival and
inoculum production of Gibberella zeae in wheat residue.
Plant Dis 88: 724–730.
Pringle A & Taylor JW (2002) The fitness of filamentous
fungi. Trends Microbiol 10: 474–481.
Scott JB & Chakraborty S (2006) Multilocus sequence analysis
of Fusarium pseudograminearum reveals a single
phylogenetic species. Mycol Res 110: 1413–1425.
Southwell RJ, Moore KJ, Manning W & Hayman PT (2003)
An outbreak of Fusarium head blight of durum wheat on
the Liverpool Plains in northern New South Wales in 1999.
Australas Plant Pathol 32: 465–471.
Stephens AE, Gardiner DM, White RG, Munn AL & Manners
JM (2008) Phases of infection and gene expression of
Fusarium graminearum during crown rot disease of wheat.
Mol Plant Microbe Interact 21: 1571–1581.
Voigt C, Scheidt B, Gácser A, Kassner H, Lieberei R, Schäfer W
& Salomon S (2007) Enhanced mycotoxin production of a
lipase-deficient Fusarium graminearum mutant correlates to
toxin-related gene expression. Eur J Plant Pathol 117: 1–12.
Wang H, Hwang SF, Eudes F, Chang KF, Howard RJ &
Turnbull GD (2006) Trichothecenes and aggressiveness of
Fusarium graminearum causing seedling blight and root rot
in cereals. Plant Pathol 55: 224–230.
Xu X & Nicholson P (2009) Community ecology of fungal
pathogens causing wheat head blight. Annu Rev Phytopathol
47: 83–103.
ª 2012 Federation of European Microbiological Societies
Published by Blackwell Publishing Ltd. All rights reserved