Globally fusarium head blight (FHB) of wheat is predominantly caused by Fusarium graminearum (FG) and crown rot (FCR) by F. pseudograminearum (FP). While both FG and FP can cause FHB in Australia, ...the reasons why the morphologically and culturally similar FG is not a major FCR pathogen has remained elusive. Using aetiology and toxigenicity, this study clarifies the contrasting roles of FG and FP in FCR and FHB in Australia. Naturally infected wheat from 42 sites during 2010 FHB epidemics, and wheat inoculated with either pathogen to induce FCR or FHB at three field plantings in 2011, were used to determine pathogen prevalence and deoxynivalenol (DON) content of the crown, stem base, stem top, rachis and grain. As the primary aetiological agent, FP prevalence in the crown correlated with FCR severity while FG in grain and/or the rachis correlated with FHB severity. FG was an effective colonizer of the crown and stem base but colonization was symptomless. DON content was linked to FG biomass in all tissues except the crown, where FP biomass was the main contributor. Of the 30 measures derived to analyse pathogen fitness in 2011, 10 described the superior fitness of FG for FHB; six defined FP fitness for FHB including inoculum dispersal; and eight defined FCR fitness of both FP and FG. FG had superior FHB fitness but weak saprophytic survival may have undermined its FCR fitness.
Wheat crops in southeast Queensland (Qld) and northern New South Wales (NSW) were infected with fusarium head blight (FHB)‐like symptoms during the 2010–11 wheat growing season. Wheat crops in this ...region were surveyed at soft dough or early maturity stage to determine the distribution, severity, aetiology and toxigenicity of FHB. FHB was widespread on bread wheat and durum, and Fusarium graminearum and/or F. pseudograminearum were diagnosed from 42 of the 44 sites using species‐specific PCR primers directly on spikelets or from monoconidial cultures obtained from spikelets. Stem base browning due to crown rot (CR) was also evident in some samples from both states. The overall FHB and CR severity was higher for NSW than Qld. Deoxynivalenol (DON) concentration of immature grains was more than 1 mg kg−1 in samples from 11 Qld and 14 NSW sites, but only 13 of 498 mature grain samples sourced from the affected areas had more than 1 mg kg−1 DON. DON concentration in straw also exceeded 1 mg kg−1 in eight Qld and all but one NSW sites but this was not linked to DON concentration of immature grains. The proportion of spikelets with positive diagnosis for F. graminearum and/or F. pseudograminearum and weather‐related factors influenced DON levels in immature grains. The average monthly rainfall for August–November during crop anthesis and maturation exceeded the long‐term monthly average by 10–150%. Weather played a critical role in FHB epidemics for Qld sites but this was not apparent for the NSW sites, as weather was generally favourable at all sites.
Fusarium crown rot (FCR) caused by the fungus
Fusarium pseudograminearum
(
Fp
) is an important disease of wheat that reduces yield and grain quality in many countries, including Australia. In this ...study, we investigated mating type idiomorph composition, putative chemotype and population genotypic structure of 98
Fp
isolates from Western Australia (WA) and the eastern Australian states of New South Wales, Victoria and South Australia. Our results revealed the expected 1:1 mating type ratio for isolates from the eastern states while there was significant variation to a 1:1 mating type composition with isolates from WA. A chemotype-specific PCR assay indicated that all
Fp
isolates from eastern states and WA segregated for the 3-ADON trichothecene chemotype. Genetic diversity assessed using 21 cleaved amplified polymorphic sequence markers revealed a high level of genotypic variation within and between
Fp
populations from eastern Australian states and WA. Analysis of molecular variance (AMOVA) showed significant difference between populations from eastern states and WA. The genetic diversity measured by Shannon index ranged from 0.95 to 2.30 with the lowest and highest values detected in Hart and Rowena populations, respectively in the eastern states. Index of association analysis showed no significant linkage of markers among isolates within 60% of the populations, suggesting that sexual reproduction may be occurring in the pathogen from those locations. These results improve understanding of
Fp
population dynamics across Australia and highlight the importance of monitoring for shifts in the population which could have implications for disease management.
Fusarium crown rot (FCR), caused predominantly by Fusarium pseudograminearum (Fp) in Australia, is an important fungal disease of wheat and barley. FCR causes significant yield losses and reduced ...grain quality worldwide. This study investigated the population dynamics of FCR‐causing F. pseudograminearum isolates from Western Australia (WA), a major wheat‐growing region. Wheat samples were collected from a total of seven different sites in 2008 and 2015. Two sites, Tammin and Karlgarin, with moderate to high FCR incidence, were intensively sampled in both years. The results revealed significant increase in Fp isolation frequency between 2008 and 2015. Over 86% of 1100 Fusarium isolates were Fp in 2015 compared with 59% of 639 isolates from 2008. Mating type idiomorphs, toxin chemotypes and population genetic structures were determined for a subset of 279 Fp isolates (132 isolates from 2008 and 165 from 2015). Mating type analysis revealed differences in MAT1‐1 and MAT1‐2 distributions between Tammin and Karlgarin for both years. Results also showed that 97.6% of Fp isolates analysed had the 3‐ADON trichothecene chemotype. Additionally, for the first time in Australia, the 15‐ADON chemotype was identified in 2.3% and 2.4% of Fp isolates from 2008 and 2015, respectively. The genetic structure of Fp population determined using 21 cleaved amplified polymorphic sequence (CAPS) markers revealed a high level of genetic variation within and between populations. In addition, 2015 isolates from Tammin and Karlgarin were significantly more aggressive (P < 0.0001) than 2008 isolates. This finding may have implications in managing this significant fungal disease.
Despite recent reports advancing our understanding of climate change on plant diseases, uncertainty remains concerning how host and pathogen interactions are changed by increases in atmospheric ...carbon-dioxide (CO2) and temperature. This study has observed crown rot inoculated and non-inoculated plants in three glasshouse environments comprising ambient CO2 with ambient temperature (E1), elevated CO2 with ambient temperature (E2) and elevated CO2 with warm temperatures (E3). The proportion of crown rot infected tillers (incidence), length of stem browning (severity) and biomass of Fusarium pseudograminearum in 16 wheat genotypes was destructively assessed at node development, anthesis, soft dough and crop maturity. Mean incidence, severity and Fusarium biomass was greater in E2, and all three measurements increased at a faster rate across plant development stages; E1 showed the lowest mean incidence and severity. Incidence and severity at each development stage was dependent on the environment each genotype was grown. The influence of genotype on Fusarium biomass at each development stage however was not seen to be dependent on environment. Irrespective of genotype plants with greater severity or relative Fusarium biomass showed lower plant dry weight at crop maturity in all environments with exception to E3, where CR severity did not exert a cost to plant dry weight. These results may allude to plant maturity and temperature-dependent resistance as effective mechanisms in building resistance to crown rot. Regardless of temperature, if crown rot symptoms and Fusarium biomass are to increase at elevated CO2 there is potential for a loss in crop production capability while boosting inoculum in crop stubble.
Experiments were conducted on olive plants in controlled environments to determine the effect of conidial concentration, leaf age, temperature, continuous and interrupted leaf wetness periods, and ...relative humidity (RH) during the drier periods that interrupted wet periods, on olive leaf spot (OLS) severity. As inoculum concentration increased from 1·0 × 10² to 2·5 × 10⁵ conidia mL⁻¹, the severity of OLS increased at all five temperatures (5, 10, 15, 20 and 25°C). A simple polynomial model satisfactorily described the relationship between the inoculum concentration at the upper asymptote (maximum number of lesions) and temperature. The results showed that for the three leaf age groups tested (2-4, 6-8 and 10-12 weeks old) OLS severity decreased significantly (P < 0·001) with increasing leaf age at the time of inoculation. Overall, temperature also affected (P < 0·001) OLS severity, with the lesion numbers increasing gradually from 5°C to a maximum at 15°C, and then declining to a minimum at 25°C. When nine leaf wetness periods (0, 6, 12, 18, 24, 36, 48, 72 and 96 h) were tested at the same temperatures, the numbers of lesions increased with increasing leaf wetness period at all temperatures tested. The minimum leaf wetness periods for infection at 5, 10, 15, 20 and 25°C were 18, 12, 12, 12 and 24 h, respectively. The wet periods during early infection processes were interrupted with drying periods (0, 3, 6, 12, 18 and 24 h) at two levels of RH (70 and 100%). The length of drying period had a significant (P < 0·001) effect on disease severity, the effect depending on the RH during the interruption. High RH (100%) resulted in greater disease severity than low RH (70%). A polynomial equation with linear and quadratic terms of temperature, wetness and leaf age was developed to describe the effects of temperature, wetness and leaf age on OLS infection, which could be incorporated as a forecasting component of an integrated system for the control of OLS.
This study examines the CO2‐mediated influence of plant resistance on crown rot dynamics under continuous cropping of partially resistant wheat line 249 and the susceptible cultivar Tamaroi. Disease ...incidence, severity, deoxynivalenol and Fusarium biomass were assessed after each cycle in microcosms established at ambient and 700 mg kg−1 CO2 using soil and stubble of these wheat lines from a field experiment with free to air CO2 enrichment. Monoconidial isolates from wheat stubble were collected initially, and after five cropping cycles, to compare the frequency and aggressiveness of Fusarium species in the two populations. Aggressiveness was measured using a high‐throughput seedling bioassay. At elevated CO2, the higher initial incidence in Tamaroi increased with cropping cycles, but incidence in 249 remained unchanged. Incidence at ambient CO2 did not change for either line. Elevated CO2 induced partial resistance in Tamaroi, but not in 249. Increased Fusarium biomass in wheat tissue at elevated CO2 matched raised deoxynivalenol of the stem base in both lines. After five cycles of continuous wheat cropping, aggressiveness increased in pathogenic F. culmorum and F. pseudograminearum by 110%, but decreased in weakly pathogenic F. equiseti and F. oxysporum by 50%. CO2 and host resistance interactively influenced species frequency, and the highly aggressive F. pseudograminearum became dominant on Tamaroi irrespective of CO2 concentration, while its frequency declined on 249. This study shows that induced resistance at elevated CO2 will not reduce crown rot severity, or impede the selection and enrichment of Fusarium populations with increased aggressiveness.
Globally fusarium head blight (
FHB
) of wheat is predominantly caused by
F
usarium graminearum
(
FG
) and crown rot (
FCR
) by
F
. pseudograminearum
(
FP
). While both
FG
and
FP
can cause
FHB
in
A
...ustralia, the reasons why the morphologically and culturally similar
FG
is not a major
FCR
pathogen has remained elusive. Using aetiology and toxigenicity, this study clarifies the contrasting roles of
FG
and
FP
in
FCR
and
FHB
in
A
ustralia. Naturally infected wheat from 42 sites during 2010
FHB
epidemics, and wheat inoculated with either pathogen to induce
FCR
or
FHB
at three field plantings in 2011, were used to determine pathogen prevalence and deoxynivalenol (
DON
) content of the crown, stem base, stem top, rachis and grain. As the primary aetiological agent,
FP
prevalence in the crown correlated with
FCR
severity while
FG
in grain and/or the rachis correlated with
FHB
severity.
FG
was an effective colonizer of the crown and stem base but colonization was symptomless.
DON
content was linked to
FG
biomass in all tissues except the crown, where
FP
biomass was the main contributor. Of the 30 measures derived to analyse pathogen fitness in 2011, 10 described the superior fitness of
FG
for
FHB
; six defined
FP
fitness for
FHB
including inoculum dispersal; and eight defined
FCR
fitness of both
FP
and
FG
.
FG
had superior
FHB
fitness but weak saprophytic survival may have undermined its
FCR
fitness.
Botrytis cinerea
is a major disease of blackcurrants causing premature flower and fruit drop in New Zealand. Because of the risk of fungicide residue from conventional methods, there is a need for ...the development of non-chemical control strategies as part of a sustainable disease control programme. Potential sources of
Botrytis cinerea
inoculum for infection of blackcurrant flowers were sampled in five blackcurrant properties in the South Island of New Zealand during dormancy and spring of 2006 and 2007. Tissues investigated were necrotic debris immediately beneath the plant, necrotic growing tips of 1-year-old canes, dead cane of previous seasons growth still attached to the base of the plant, canes damaged by harvesting or pruning, and canes damaged by currant clearwing (
Synanthedon tipuliformis
). The mean number of each tissue type within a plant varied considerably, both within a property and between different properties. Necrotic debris immediately beneath the plant and necrotic cane tips were shown to be the main sources of inoculum. Knowledge of the main sources of inoculum is an important first step towards the development of new, non-chemical control strategies, which are discussed in this context.
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