Fusarium Head Blight Isolates Research Articles

Adaptation of Fusarium Species causing Head Blight to Quantitative Resistance in Wheat: Field Evidence for Increased Aggressiveness in a New Pathogen Population

The use of quantitatively resistant wheat cultivars is an essential component of a sustainable management strategy of Fusarium head blight (FHB), caused by several Fusarium species. However, little information is available on the variation of aggressiveness of the newly emerging FHB collection compared to old one. It is therefore important to determine to what extent FHB populations can be selected for increased aggressiveness by wheat cultivars with several levels of quantitative resistance. To this end, FHB populations were sampled in 2005 (old population) and in 2015 (new population) from one of the major Syrian wheat production regions, chosen as a location where head blight occurs regularly. New and old FHB isolates were characterized for aggressiveness by single-floret inoculation under controlled conditions on eight durum and bread wheat cultivars of contrasting susceptibility to FHB, and molecularly distinguished using DNA markers. Results showed the new population caused a higher disease severity (ranging from 55% to 67%) than the old population. Thus, their aggressiveness increased between early and late samplings, suggesting that wheat plants cultivated over 10 years selected for increased aggressiveness during epidemics. Our comparative population genetic analyses with analyzed markers showed that the new population had more polymorphic loci compared with the old one. The information obtained in this study indicated that FHB populations adapt to prevailing wheat cultivars, irrespective of their resistance levels, and can therefore overcome polygenic, quantitative resistance. Adaptation to wheat resulting in increased pathogen aggressiveness that was not specific may render quantitative resistance nondurable if not properly managed

A simple and reliable assay to quantify host resistance and aggressiveness of the pathogen in the Fusarium head blight-barley pathosystem

Abstract A simple and reliable method for quantifying Fusarium head blight (FHB), a widespread disease of barley, would enhance our capacity in identifying resistance sources and highly aggressive isolates. A detached head assay (DHA) was used to reliably assess: (i) resistance of two barley cultivars, Arabi Aswad (AS) and Arabi Abiad (AB) with different susceptibility to FHB and (ii) aggressiveness in a set of 16 fungal isolates of four Fusarium species. The two inoculated cultivars showed different responses in FHB incidence (DI) and severity (DS) using spray and point inoculation on detached barley heads, respectively. On AB, susceptible under several experimental conditions, inoculation with different Fusarium species resulted in significantly higher DI and DS, compared with AS, which showed Fusarium resistance. Furthermore, the values of DI and DS were significantly correlated with the previous findings generated under several experimental conditions. The use of this simple and reliable method in barley breeding programs can speed up the process of identification of sources of resistance to multiple FHB isolates. To our best knowledge, this is the first in-depth report investigating the usefulness of DHA for distinguishing susceptibility of barley plants and aggressiveness of diverse Fusarium species from a breeder's point of view.

Screening for wheat resistance and pathogenicity of Fusarium head blight species using an in vitro detached head test

Fusarium head blight (FHB) is a major disease on wheat crop leading to significant yield losses and poor quality of infected grains worldwide. From a breeder’s point of view, a simple and reliable test for assessing this disease would enhance our capacity in identifying wheat resistance sources and highly pathogenic isolates. To achieve this objective, a test involving the inoculation of a detached head (DHT) maintained in vitro was used to determine the reaction of six durum and bread wheat cultivars to disease and pathogenicity of four Fusarium species. The estimation of disease incidence and disease severity detected using spray and point inoculation on detached wheat heads, respectively, enabled discrimination among wheat cultivars differing in their susceptibility to the pathogen and 16 FHB isolates of contrasting pathogenicity. Significant correlations were found between in vitro DHT values in seedlings and adult plants, highlighting that this testing procedure was reliable. The established assay using in vitro DHT in this first in-depth report enables a simple, fast and reliable screening of the susceptibility of durum and bread wheat to FHB pathogens and pathogenicity of diverse Fusarium species and should be useful for many types of studies on this disease.

Disease Resistance and Genes in 146 Wheat Cultivars (Lines) from the Huang-Huai-Hai Region of China

Wheat stripe rust, powdery mildew, and Fusarium head blight (FHB) are the three most important diseases in wheat worldwide. Growing resistant cultivars is the most economic and effective method to control these diseases. To assess the disease resistance of commercial wheat cultivars and regional trial wheat lines in the Huang-Huai-Hai region of China, 146 wheat entries were inoculated with the Chinese prevalent Puccinia striiformis f. sp. tritici (Pst) races CYR32, CYR33, CYR34, and Blumeria graminis f. sp. tritici (Bgt) isolate E09 under controlled greenhouse conditions, respectively; these entries were also tested with the mixed Pst races, Bgt and FHB isolates at adult-plant stage in the field, respectively. The results showed that 108 (73.97%), 83 (56.85%), 99 (67.81%), and 22 (15.07%) entries were resistant to CYR32, CYR33, CYR34, and E09 at the seedling stage, respectively; 102 (69.86%), 24 (16.44%), and 2 (1.37%) entries were resistant to stripe rust, powdery mildew, and Fusarium head blight at the adult-plant stage, respectively. Additionally, the possible resistance gene(s) in these entries were postulated by the closely linked markers of stripe rust resistance genes Yr5, Yr9, Yr10, Yr15, Yr17, Yr18, Yr26, powdery mildew resistance gene Pm21, and Fusarium head blight resistance gene Fhb1. Combined with disease resistance and molecular markers tests, 62, nine, and three wheat entries were postulated to carry the Yr9, Yr17, Yr26 gene, respectively, and no entries contained Yr5, Yr10, Yr15, Yr18, Pm21, and Fhb1 gene. This study laid a theoretical foundation for rational utilization of these entries and gene in wheat breeding programs and disease control.

An Efficient in vitro Assay to Predict Resistance and Pathogenicity in the Fusarium Head Blight-Hordeum Vulgare Pathosystem

Background: Barley (Hordeum vulgare L.) worldwide is affected seriously by Fusarium Head Blight (FHB) disease caused by several Fusarium species. In vitro assays permitting for easy, efficient and reliable prediction of the head blight reaction in the whole plant should be investigated. Objective and Methods: The in vitro ability of 16 fungal isolates of four FHB species to confer disease on individual plant organs was evaluated using a coleoptile infection assay. Four quantitative components (Seed Germination (SG), Coleoptile Length (CL), Coleoptile Weight (CW) and Root Weight (RW)) were analyzed in two widely cultivated barley cultivars, Arabi Aswad (AS) and Arabi Abiad (AB), with known quantitative resistance. Results: Differences in inoculated pathogenicity and resistance treatments were observed on young plant parts relative to water controls, indicating that these FHB species were found to be suitable for the differential expression of all tested quantitative components. There was a wide variation in pathogenicity among the 16 FHB isolates and susceptibility among AS and AB. The 16 FHB isolates can be separated into the first group with larger number of isolates, upon infection with which AB really was more susceptible to FHB infection than AS, and isolates of the second group with leaser number of isolates for which AS and AB react was the opposite. On AB, rather susceptible, inoculation with FHB species resulted in significantly less SG, CL, CW and RW, compared with AS, which showed a greater resistance. The very good resistance of AS was confirmed by the measurements of quantitative resistance components described in this study. When infected with FHB isolates, all indicators of a more susceptible cultivar seemed to be 10-20% less than those of a resistant cultivar. Moreover, the values of all analyzed components were significantly correlated with the data of pathogenic indices generated in vitro, and under controlled and field conditions with a large diversity depending on AS and AB. Conclusion: Appropriate in vitro conditions were determined for the coleoptile infection assay to maximize differences in disease reactions components among FHB isolates and the two barley cultivars. Results suggest that all measured components predict resistance and pathogenicity occurring at the earliest and latest barley development stages during FHB infection. Our data also highlighted, for the first time, the utility of CW and RW for the determination of resistance and pathogenicity in the FHB-barley pathosystem. The coleoptile infection test was confirmed to be adequate to in vitro, growth chamber and field data by the presence of the first group, which prevailed in all other tests generated under different experimental conditions. The in vitro coleoptile infection assay may offer a real possibility of simple, rapid and reliable screening of resistance in barley cultivars and pathogenicity of FHB species.

Aggressiveness of Fusarium species causing head blight on wheat plants determined in detached leaf and seedling in vitro assays

Fusarium head blight (FHB) is a serious disease of wheat. In vitro assays for reliable prediction of the head blight reaction in whole plant was investigated. The capacity of 16 fungal isolates of four FHB species to cause disease on individual plant organs was evaluated in vitro. Six quantitative components related to detached leaf and seedling assays were analyzed in six durum and bread wheat cultivars with known resistance. Differences in inoculated treatment were observed on young plant parts relative to water controls, indicating that these FHB species were found to be suitable for the differential expression of all tested quantitative components. There was a wide variation in aggressiveness among the 16 FHB isolates for latent period (LP) in detached leaf assay. Nevertheless, the other five components: incubation period and lesion length of detached leaf assay, percentage of infected seedlings (of foliar-spraying and pin-point inoculations) and lesion length (of clip-dipping inoculation) did not distinguish isolates. Significant correlation was found for the aggressiveness measured by LP of 16 FHB isolates and the previous pathogenic component ratings generated in vitro and in growth chamber and field study. These results suggest that LP predicts aggressiveness occurring at the earliest and latest wheat development stages during FHB infection. To our best knowledge, this is the primary in-depth report combining six different quantitative components delivered from two distinct in vitro assays to quantify aggressiveness in FHB species complex. Our data also highlighted, for the first time, the utility of LP for rapid and early determination of aggressiveness in FHB-wheat pathosystem.

Pathogenic variability of Fusarium head blight species on durum wheat plants determined using in vitro detached leaf and seedling assays

Fusarium head blight (FHB) is an economically important disease of wheat globally, but few publications have appeared on assessing quantitative component of pathogenicity of FHB species in vitro. In this context, the aggressiveness of 16 isolates of four FHB species was quantified on a durum wheat cultivar with a moderate resistance to FHB infection. Two in vitro assays (detached leaf and seedling tests), which yielded six aggressiveness criteria, were used. Results showed differences between treatments inoculated with FHB isolates and control for all tested criteria. Regarding latent period of detached leaf test, variability in aggressiveness within and among the species was detected. The other five criteria: incubation period and lesion length of detached leaf test, percentage of infected seedlings (of foliar-spraying and pin-point inoculations) and lesion length (of clip-dipping inoculation) did not distinguish FHB isolates. Taking into consideration in vitro and the artificial inoculation findings generated under different experimental conditions, significant correlations were found between latent period and these pathogenic indices. Therefore, the idea of using the in vitro criterion: latent period appears to be established based on its predictive ability of aggressiveness occurring at the earliest and latest wheat development stages during FHB infection.

VARIATION IN AGGRESSIVENESS OF FUSARIUM HEAD BLIGHT SPECIES TOWARDS BARLEY PLANTS DETERMINED USING THREE IN VITRO ASSAYS

Aggressiveness is the most important fungal trait affecting Fusarium head blight (FHB) disease invasion and stability of host resistance. Until recently, in vitro methodologies have proved to be very useful in analyzing disease responses in barley plants to FHB infection. To update our knowledge, the variation in aggressiveness for 16 isolates of four FHB species was assessed towards two barley cultivars varying in resistance to FHB. Nine aggressiveness criteria involved in three in vitro assays were used: incubation period, latent period (LP), lesion length (of detached leaf and clip-dipping inoculations), germination rate reduction, standardized area under disease progress curve (AUDPCstandard), coleoptile length reduction of Petri-dish inoculation, and percentage of infected seedlings (of foliar-spraying and pin-point inoculations). Differences in inoculated treatment were observed on young plant parts relative to water controls. Inter and intraspecific differences in aggressiveness were observed towards barley plants as measured by LP and AUDPCstandard. Nevertheless, the other seven criteria did not differentiate FHB isolates. Results indicted that a cultivar-specific aggressiveness do not exist among barley plants and pathogens for LP and AUDPCstandard. Significant correlation coefficients were obtained between the data of LP and AUDPCstandard. Moreover, the values of LP and AUDPCstandard were significantly correlated with the data of disease incidence generated under controlled and field conditions. It seems that LP and AUDPCstandard are indicators of aggressiveness occurring in the whole plant during FHB infection. To our best knowledge, this is the first in vitro research full analyzing aggressiveness of four FHB species on barley plants. In addition, our study investigates the potential use of in vitro indices in predicting FHB data generated under controlled and field conditions.

In Vitro Quantitative Resistance Components in Wheat Plants to Fusarium Head Blight

Background: In vitro tools have proved to be very useful in identifying quantitative resistance in wheat to Fusarium Head Blight (FHB) infection. However, there is a need to understand how the different in vitro and in planta tests correlate to describe the level of wheat resistance to FHB infection. Objective and Methods: We evaluated the correlation between in vitro symptom assessment using nine quantitative resistance criteria and in planta disease severity for Type II resistance assessment using a set of 16 FHB isolates across two widely grown Syrian wheat cultivars: Cham1 (durum) and Cham6 (bread). Results: Cultivar differences after inoculation with fungal isolates in seedlings and adult plants relative to the controls were detected. There were significant differences in the resistance of two wheat cultivars as measured by adult FHB resistance, Latent Period (LP) of detached leaf inoculation and standardized Area Under Disease Progress Curve (AUDPCstandard) of modified Petri-dish inoculation. Correlation coefficients between FHB severity and the two in vitro components LP and AUDPCstandard were significant (r=0.545 with p<0.05, and r=0.659 with p<0.01, respectively). No significant differences in the resistance of Cham6 and Cham1 were indicated for the other seven in vitro components: incubation period and lesion length of detached leaf inoculation, germination rate reduction and coleoptile length reduction of modified Petri-dish inoculation and lesion length of clip-dipping inoculation and percentage of infected seedlings of foliar-spraying and pin-point inoculations. Results from these seven components were not correlated with adult FHB resistance. Longer latent period and less AUDPCstandard were related to greater FHB disease-type II resistance. Conclusion: LP and AUDPCstandard are indicators of mechanisms of resistance occurring in the whole plant during FHB infection. Therefore, the idea of using in vitro components is based on their predictive ability of in planta adult FHB resistance.

Intra- and inter-species variability of the aggressiveness in four Fusarium head blight species on durum wheat plants detected in an in vitro Petri-dish assay

Aggressiveness assessment of Fusarium head blight (FHB) is crucial for explaining the interaction in FHB–wheat association. Currently, in vitro tools have proved to be very useful in identifying disease responses in wheat to FHB infection. To update our knowledge, intra- and inter-species variability of the aggressiveness was studied in 16 isolates of four FHB species (F. culmorum, F. solani, F. verticillioides and F. equiseti) using an in vitro Petri-dish test. Three aggressiveness criteria, germination rate reduction, standardised area under disease progress curve (AUDPCstandard) and coleoptile length reduction, were evaluated on a durum wheat cultivar showing a moderate level of quantitative resistance. Regarding AUDPCstandard, intra- and inter-species variability was detected. The other two aggressiveness criteria did not distinguish isolates within and among species. The three aggressiveness criteria were not significantly correlated. However, it was not possible to cluster the isolates based on their species origins because of similarity in pathogenic level among the 16 fungal isolates. The results provide evidence that there is a differential interaction between quantitative resistance genes in wheat plants and the 16 tested FHB isolates. The values of AUDPCstandard showed significant correlation with both: disease incidence and disease severity obtained under controlled conditions (r = 0.627** and r = 0.539*, respectively), and disease incidence generated by field conditions (r = 0.525*). AUDPCstandard could be of potential use in evaluating the aggressiveness of FHB in adult wheat plants under controlled and field conditions.

Species composition, toxigenic potential and aggressiveness of Fusarium isolates causing Head Blight of barley in Uruguay

Fusarium Head Blight (FHB) is a major constraint to barley production that substantially reduces yield and grain quality. FHB is also a major food safety concern because FHB pathogens contaminate grain with trichothecenes and other mycotoxins. DNA sequence-based analyses and in-vitro toxin assessments were used to characterize the species and trichothecene chemotype composition of FHB pathogens on barley in Uruguay. F. graminearum was the dominant species (89.7%), and three other members of the F. graminearum species complex (FGSC) were identified as FHB pathogens of barley in Uruguay for the first time. Other minor contributors to FHB species diversity included F. poae, F. avenaceum, F. pseudograminearum and an unnamed species from the F. incarnatum-equiseti species complex (FIESC). Most isolates (89.7%) had the 15-acetyldeoxynivalenol (15-ADON) trichothecene type. However, the results expanded the known area of occurrence within Uruguay for the nivalenol (NIV) toxin type, which was observed among isolates from three species of the FGSC, F. pseudograminearum, and F. poae. Isolates with the 3-acetyldeoxynivalenol (3-ADON) or NX-2 toxin types were not observed, although a previously published multilocus genotyping assay was updated to identify NX-2 strains. Analyses of population structure and comparisons with FHB isolates from wheat in Uruguay indicated that F. graminearum constitutes a single genetic population with no evidence of population differentiation related to the sampled hosts. Inter and intraspecific differences were observed in aggressiveness toward four barley genotypes with different levels of resistance to FHB, and in general nivalenol producers were the least aggressive isolates. Sensitivity to metconazole was approximately 10 times higher than was detected for tebuconazole. This is the first report regarding tebuconazole and metconazole sensitivity for Fusarium species causing FHB in barley in Uruguay, and constitutes an important starting point for monitoring temporal or spatial changes in FGSC sensitivity, which is critical to define FHB management practices.

Regional differences in the composition of Fusarium Head Blight pathogens and mycotoxins associated with wheat in Mexico

Fusarium Head Blight (FHB) is a destructive disease of small grain cereals and a major food safety concern. Epidemics result in substantial yield losses, reduction in crop quality, and contamination of grains with trichothecenes and other mycotoxins. A number of different fusaria can cause FHB, and there are significant regional differences in the occurrence and prevalence of FHB pathogen species and their associated mycotoxins. Information on FHB pathogen and mycotoxin diversity in Mexico has been extremely limited, but is needed to improve disease and mycotoxin control efforts. To address this, we used a combination of DNA sequence-based methods and in-vitro toxin analyses to characterize FHB isolates collected from symptomatic wheat in Mexico during the 2013 and 2014 growing seasons. Among 116 Fusarium isolates, we identified five species complexes including nine named Fusarium species and 30 isolates representing unnamed or potentially novel species. Significant regional differences (P < 0.001) in pathogen composition were observed, with F. boothii accounting for >90% of isolates from the Mixteca region in southern Mexico, whereas F. avenaceum and related members of the F. tricinctum species complex (FTSC) accounted for nearly 75% of isolates from the Highlands region in Central Mexico. F. graminearum, which is the dominant FHB pathogen in other parts of North America, was not present among the isolates from Mexico. F. boothii isolates had the 15-acetyldeoxynivalenol toxin type, and some of the minor FHB species produced trichothecenes, such as nivalenol, T-2 toxin and diacetoxyscirpenol. None of the FTSC isolates tested was able to produce trichothecenes, but many produced chlamydosporol and enniatin B.

Aggressiveness variation among and within Fusarium head blight species on barley in vitro

Aggressiveness variation among 16 isolates of four Fusarium species (F. culmorum, F. solani, F. verticillioides and F. equiseti) causing Fusarium head blight (FHB) was studied in vitro. Evaluation of three aggressiveness criteria involved in a Petri-dish test: germination rate reduction, standardized area under disease progress curve (AUDPCstandard), and coleoptile length reduction was carried out on the barley cultivar Arabi Aswad. Results showed differences between barley plants inoculated with FHB isolates and control for the three tested aggressiveness criteria. Regarding AUDPCstandard and Petri-dish aggressiveness index which is calculated from the mean value of three aggressiveness criteria, within and among variation was detected. Intra- and inter-species variability was not distinguished for the other two aggressiveness criteria. However, pathogenic level observed among 16 isolates can not be differentiated within the four FHB species. Significant correlation was detected only between AUDPCstandard and Petri-dish aggressiveness index. The results were comparable with those previously obtained using the same fungal isolates on wheat cultivar in vitro. It seems that FHB isolates recovered from wheat spikes and tested on wheat plants showed a similar range of aggressiveness on a barley cultivar, Arabi Aswad.

In vitro assessment of Fusarium head blight spp. on wheat cultivars

Aggressiveness in four isolates of Fusarium head blight (FHB) species (F. culmorum, F. solani, F. verticillioides and F. equiesti) was studied in vitro on six wheat cultivars using a modified Petri-dish test. Results showed differences between cultivars inoculated with FHB isolates and control for three aggressiveness criteria: germination rate reduction, standardised area under disease progress curve (AUDPCstandard), and coleoptile length reduction. Regarding AUDPCstandard and Petri-dish aggressiveness index, significant differences were detected among fungal isolates. The other two aggressiveness criteria: germination rate reduction and coleoptile length reduction did not distinguish between FHB isolates. The Petri-dish test was repeatable and stable method to assess aggressiveness of four FHB species for all tested wheat cultivars. The current study confirmed the suitability of in vitro modified Petri-dish method to be used as fast and reliable test to analyse aggressiveness in FHB species.

Analysis of Fusarium graminearum Species Complex from Wheat-Maize Rotation Regions in Henan (China).

Fusarium head blight (FHB) and maize stalk rot (MSR), caused by members of the Fusarium graminearum species complex (FGSC), are among the most destructive and economically important diseases in the world. Species identity and the trichothecene chemotype of 312 members of the FGSC from diseased wheat spikes and maize stalks in Henan was determined using phylogenetic analyses and a polymerase chain reaction trichothecene chemotype assay. F. graminearum sensu stricto accounted for more than 93% of the FGSC isolates associated with FHB (N = 168) and MSR (N = 130). The remaining isolates were F. asiaticum. Significant differences were found in the frequencies of the two species within the hosts (P < 0.01). However, the frequencies of the same species in FHB and MSR were similar (P > 0.05) for wheat and maize isolates, indicating that the composition of the FGSC with respect to wheat and maize in these fields varied little. The 15-acetyl-deoxynivalenol (15-ADON) trichothecene chemotype represented 92.7 and 98.5% of isolates from wheat (N = 167) and maize (N = 130), respectively. However, the 3-acetyl-deoxynivalenol chemotype was found in 6.7% of wheat isolates, and the nivalenol chemotype in 1.5% of MSR isolates and in 0.6% of FHB isolates. Mycelial growth at different concentrations of carbendazim and difenoconazole did not differ between F. graminearum sensu stricto and F. asiaticum. These results suggest that the 15-ADON chemotype of F. graminearum sensu stricto is the predominant pathogen that causes wheat- and maize-related diseases in this region. Copyright © 2017 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Regional differences in species composition and toxigenic potential among Fusarium head blight isolates from Uruguay indicate a risk of nivalenol contamination in new wheat production areas

Members of the Fusarium graminearum species complex (FGSC) are the primary cause of Fusarium head blight (FHB) of wheat, and frequently contaminate grain with trichothecene mycotoxins that pose a serious threat to food safety and animal health. The species identity and trichothecene toxin potential of 151 FGSC isolates collected from wheat in Uruguay were determined via multilocus genotyping. Although F. graminearum with the 15ADON trichothecene type accounted for 86% of the isolates examined, five different FGSC species and all three trichothecene types were identified in this collection. This is the first report of Fusarium asiaticum, Fusarium brasilicum, Fusarium cortaderiae, and Fusarium austroamericanum from Uruguay. In addition, we observed significant (P<0.001) regional differences in the composition of FGSC species and trichothecene types within Uruguay. Isolates of F. graminearum with the 15ADON type were the most prevalent in western provinces (95%), while F. asiaticum (43%) and the NIV type (61%) predominated in the new wheat production zone in Cerro Largo along Uruguay's eastern border with Brazil. F. graminearum isolates (15ADON type) were significantly (P<0.005) more aggressive on wheat than were isolates from the other species examined (NIV or 3ADON types). However, F. graminearum isolates (15ADON type) were significantly (P<0.05) more sensitive to tebuconazole than isolates from other species (NIV type). These results document substantial heterogeneity among the pathogens responsible for FHB in Uruguay. In addition, the regional predominance of the NIV trichothecene type is of significant concern to food safety and indicates that additional monitoring of nivalenol levels in grain may be required.

Analysis of the Fusariumgraminearum species complex from wheat, barley and maize in South Africa provides evidence of species-specific differences in host preference

Species identity and trichothecene toxin potential of 560 members of the Fusarium graminearum species complex (FGSC) collected from diseased wheat, barley and maize in South Africa was determined using a microsphere-based multilocus genotyping assay. Although three trichothecene types (3-ADON, 15-ADON and NIV) were represented among these isolates, strains with the 15-ADON type predominated on all three hosts. A significant difference, however, was identified in the composition of FGSC pathogens associated with Gibberella ear rot (GER) of maize as compared to Fusarium head blight (FHB) of wheat or barley ( P < 0.001). F. graminearum accounted for more than 85% of the FGSC isolates associated with FHB of wheat and barley ( N = 425), and was also the dominant species among isolates from maize roots ( N = 35). However, with the exception of a single isolate identified as an interspecific hybrid between Fusarium boothii and F. graminearum, GER of maize ( N = 100) was exclusively associated with F. boothii. The predominance of F. graminearum among FHB isolates, and the near exclusivity of F. boothiii among GER isolates, was observed across all cultivars, collection dates, and provinces sampled. Because these results suggest a difference in host preference among species of the FGSC, we hypothesize that F. graminearum may be less well adapted to infect maize ears than other members of the FGSC.

Global molecular surveillance reveals novel Fusarium head blight species and trichothecene toxin diversity

To expand our knowledge of Fusarium head blight (FHB) pathogen and trichothecene toxin diversity, a global collection of 2100 isolates was screened for novel genetic variation, resulting in the identification of 16 phylogenetically divergent FHB isolates. The affinities and taxonomic status of these novel isolates were evaluated via phylogenetic analyses of multilocus DNA sequence data (13 genes; 16.3 kb/strain) together with analyses of their morphology, pathogenicity to wheat, and trichothecene toxin potential. Based on the results of these analyses, we formally describe two novel species ( Fusarium vorosii and Fusarium gerlachii) within the Fusarium graminearum species complex ( Fg complex), and provide the first published report of Fg complex isolates with either a nivalenol or 3-acetyldeoxynivalenol chemotype within the U.S. In addition, we describe a highly divergent population of F. graminearum from the Gulf Coast of the U.S., and divergent isolates of F. acaciae- mearnsii from Australia and South Africa.