Graminearum Isolates Research Articles

Genetic Diversity and Population Structure of Head Blight Disease Causing Fungus Fusarium graminearum in Northern Wheat Belt of India.

Head blight or scab caused by Fusarium graminearum (FG), once ranked as a minor disease in wheat, is now emerging as one of the economically important diseases in India. The present study represents the first in-depth population genetic analysis of the FG from the northern wheat belt of India. In this study, multiple conserved gene sequences comprised of β-tubulin (TUB), translation elongation factor 1-α (TEF), and histone-3 (HIS) regions were used for multi-locus phylogenetic analysis of 123 geographically distinct F. graminearum isolates collected from four different states (Haryana (HR), Punjab (PB), Rajasthan (RJ) and West Bengal (WB)) of India. The phylogenetic and haplotype analysis showed the presence of thirty haplotypes in all the analyzed populations. The haplotypic diversity in the RJ population (Hd = 0.981) was higher than in the HR (Hd = 0.972), PB (Hd = 0.965) and WB population (Hd = 0.962). Recombination events (Rm = 12) and mutation events (485) were also detected. Analysis of molecular variance (AMOVA) indicated that genetic diversity was exclusively due to the differences within populations. The haplotype network was widely dispersed and not associated with specific populations, as a single common haplotype was not detected. The PB population contained both unique (H9, H10 and H11) and shared haplotypes (27 haplotypes) in a higher number in comparison to other geographical locations. Except for haplotype H22 (contains highly aggressive isolates), there was no specific linkage noticed between the isolate aggressiveness and haplotype. The concatenated sequences of all the three genes demonstrated a low level of genetic differentiation (Fst = −0.014 to 0.02) in the analyzed population. Positive values for the neutrality tests in PB, HR and RJ reveal a balancing selection mechanism behind the FG population structure. The WB population showed both positive and negative values of neutrality indices, indicating the role of both population expansion as well as balancing selection in structuring the FG population.

Fusarium Graminearum Virus-1 Strain FgV1-SD4 Infection Eliminates Mycotoxin Deoxynivalenol Synthesis by Fusarium graminearum in FHB.

Deoxynivalenol (DON) toxin production during the infection of F. graminearum in small grain crops is one of the most harmful virulence factors associated with economic losses. Metatranscriptome sequencing and RT-qPCR traced back that the only mycovirus infecting an F. graminearum isolate, designated as Fg-4-2, was a novel strain of Fusarium graminearum virus 1 (FgV1), designated as FgV1-SD4. The isolate Fg-4-2 showed significantly reduced virulence against wheat compared to the virus-free culture, designated as isolate Fg-4-1, which was obtained by deep freezing and single conidial germination. Notably, no DON accumulation was detected in the harvested wheat seeds infected by Fg-4-2, whereas ~18 ppm DON was detected in seeds infected by Fg-4-1. Comparison of the genome sequence of FgV1-SD4 with other identified strains of FgV1, i.e., FgV1-DK21 and FgV1-ch, indicates mutations on ORF-2 and the 3′-UTR in the genome that might be associated with hypovirulence. This mycovirus strain alone and specific genetic components of FgV1-SD4 can be further optimized to be developed as a biocontrol agent to reduce Fusarium head blight and to lower the DON accumulation levels in small grain crops due to this fungal disease.

The Black Necrotic Lesion Enhanced Fusarium graminearum Resistance in Wheat.

Fusarium head blight, mainly incited by Fusarium graminearum, is a devastating wheat disease worldwide. Diverse Fusarium head blight (FHB) resistant sources have been reported, but the resistance mechanisms of these sources remain to be investigated. FHB-resistant wheat germplasm often shows black necrotic lesions (BNLs) around the infection sites. To determine the relationship between BNL and FHB resistance, leaf tissue of a resistant wheat cultivar Sumai 3 was inoculated with four different F. graminearum isolates. Integrated metabolomic and transcriptomic analyses of the inoculated samples suggested that the phytohormone signaling, phenolamine, and flavonoid metabolic pathways played important roles in BNL formation that restricted F. graminearum extension. Exogenous application of flavonoid metabolites on wheat detached leaves revealed the possible contribution of flavonoids to BNL formation. Exogenous treatment of either salicylic acid (SA) or methyl jasmonate (MeJA) on wheat spikes significantly reduced the FHB severity. However, exogenous MeJA treatment prevented the BNL formation on the detached leaves of FHB-resistant wheat Sumai 3. SA signaling pathway influenced reactive oxygen species (ROS) burst to enhance BNL formation to reduce FHB severity. Three key genes in SA biosynthesis and signal transduction pathway, TaICS1, TaNPR1, and TaNPR3, positively regulated FHB resistance in wheat. A complex temporal interaction that contributed to wheat FHB resistance was detected between the SA and JA signaling pathways. Knowledge of BNLs extends our understanding of the molecular mechanisms of FHB resistance in wheat and will benefit the genetic improvement of wheat FHB resistance.

Fusarium blight of common buckwheat in Primorsky krai

Relevance . Common buckwheat is one of the most important cereal and melliferous crops being in demand both in Russia and overseas. Despite the fact that buckwheat has lower sus- ceptibility to infectious diseases in comparisons with other grain and cereal crops, research on its pathogens is a topical issue considering a high disease rate for this crop in Primorsky krai. Materials and methods. The study on pathogenic composition was conducted in selective crop rotations of FSBSI “FSC of Agricultural Biotechnology of the Far East named after A.K. Chaiki” at the territory of Ussuriysky district in Primorsky krai. Indeterminate (Izumrud, Pri 7, Bashkirskaya krasnostebel’naya) and determinate (Dikul) buckwheat varieties were used for the study. Fungi were isolated from rhizoplane using water washing technique, from soil and rhizosphere via the dilution method, from leaves and root systems by accumulation in a moist chamber with subsequent transfer of culture onto selective medium. Fungal isolates were cul- tivated on toxigenic medium (Myro) to determine their phytotoxicity. Phytopathogenic activity of living cultures was evaluated on potato sucrose agar according to the modified method of Chelkowski and Manka . All experiments were conducted in accordance with established methods. Results . Culture filtrates of F. avenaceum and F. graminearum isolates, obtained from different anatomical parts of common buckwheat, were characterized by low toxicity, and culture filtrates of F. oxysporum isolate were highly toxic. Phytotoxicity of pathogens manifested itself not only in decrease in laboratory germination ability of buckwheat seeds, but also in inhibition of buckwheat sprout development. It proved that metabolites exerted a prolonged effect on sensitive plants. F.avenaceum, F. oxysporum and F. graminearum have pronounced phy- topathogenic and aggressive properties in relation to buckwheat and test-plants in the laboratory conditions. The sum total of their studied phytotoxic properties is convincing enough to consider them potentially hazardous to buckwheat for wilt disease development.

Fusarium Head Blight of Small Grains in Pennsylvania: Unravelling Species Diversity, Toxin Types, Growth, and Triazole Sensitivity.

Fusarium graminearum is the main causal species of Fusarium head blight (FHB) globally. Recent changes in the trichothecene (toxin) types in the North American FHB pathogens support the need for continued surveillance. In this study, 461 isolates were obtained from symptomatic spikes of wheat, spelt, barley, and rye crops during 2018 and 2019. These were all identified to species and toxin types using molecular-based approaches. An additional set of 77 F. graminearum isolates obtained from overwintering crop residues during winter 2012 were molecularly identified to toxin types. A subset of 31 F. graminearum isolates (15 15-acetyl-deoxynivalenol [15ADON] and 16 3-acetyl-deoxynivalenol [3ADON]) were assessed for mycelial growth, macroconidia, perithecia, and ascospore production, and sensitivity to two triazoles. Ninety percent of isolates obtained from the symptomatic spikes (n = 418) belonged to F. graminearum, with four other species found at a lower frequency (n = 39). The F. graminearum isolates from symptomatic spikes were mainly of the 15ADON (95%), followed by 3ADON (4%), nivalenol (0.7%), and NX-2 (0.3%) toxin types. All F. graminearum isolates obtained from overwintering residue were of the 15ADON type. The toxin types could not be differentiated based on the multivariate analysis of growth and reproduction traits. All isolates were sensitive to tebuconazole and metconazole fungicides invitro. This study confirms the dominance of F. graminearum and suggests ecological and environmental factors, to be further identified, that lead to similar composition of toxin types in the northern United States. Our results may be useful to assess the sustainability of FHB management practices and provide a baseline for future FHB surveys.

First report of Head blight of wheat caused by Fusarium vorosii in Serbia.

The cosmopolitan species Fusarium graminearum Schwabe directly reduces yield, as well as grain quality of cereals, due to its ability to synthesize mycotoxins. Previously it was considered to be one species occurring on all continents. However, phylogenetic analysis employing the GCPSR method (Genealogical Concordance Phylogenetic Species Recognition) revealed the existence of 15 phylogenetic species within what is now recognised as the Fusarium graminearum Species Complex (FGSC) (Sarver et al. 2011). During 1996-2008, a MRIZP collection of FGSC isolates was established and isolates originating from wheat (5), maize (3) and barely (2) were selected for further study. Morphological features including the appearance of colonies and macroconidia (average size 38.5-53.1 × 4.6-5.4 µm, No 50) of all 10 isolates on PDA were consistent with descriptions of F. graminearum (O'Donnell et al. 2004, Leslie and Summerell 2006). Total DNA was isolated from mycelium removed from 7-day old colonies of single-spore isolates grown on PDA using the DNeasy Plant Mini Kit (Qiagen, Hilden). Further identification was based on amplification and sequencing of elongation factor TEF-1α, histone H3 and β-tubulin in both directions, with primers ef1/ef2, H3-1a/H3-1b and T1/T22, respectively (Jacobs et al. 2010). The sequences were deposited in NCBI under accession numbers MF974399 - MF974408 (TEF-1α), MG063783 - MG063792 (β-tubulin) and MF999139 - MF999148 (histone H3). Sequence analysis was performed using BLAST while genetic similarity was calculated using MEGA 6.0 software. Isolate 1339 originating from wheat (collected at the locality of Kikinda in 2006), shared 100% nucleotide identity with TEF-1α (DQ459745), histone H3 (DQ459728) and β-tubulin (DQ459643) of F. vorosii isolate NRRL37605 (Starkey et al. 2007). The remaining nine isolates were identified as F. graminearum as they shared 99% to 100% nucleotide similarity with F. graminearum NRRL 28439 (O'Donnell et al. 2004). Pathogenicity was tested using artificial inoculations of spikes during wheat flowering (Mesterhazy et al. 1999). Thirty classes were inoculated with each isolate, in three replicates. Inoculum was prepared from 7-day colonies on PDA, and 30 ml of a conidia suspension (1x105 conidia/ml) was used. Control plants were inoculated with sterile water. Three weeks after inoculation, typical Fusarium head blight symptoms were visible on inoculated plants, from which all 10 isolates were successfully reisolated. Control spikes remained symptomless. Disease severity was estimated on the 1-7 scale (Blandino et al. 2012). Average pathogenicity of the F. vorosii isolate 1339 was 1.9, and 2.4 -5.1 of F. graminearum isolates. Toxin production was determined using gas chromatography-tandem mass spectrometry. Kernels inoculated with the 10 isolates were ground and tested for the presence of deoxynivalenol (DON) and its acetyl derivatives 3ADON, 15ADON and NIV. F. vorosii isolate 1339 possessed the 15ADON chemotype, as well as eight F. graminearum isolates, while only one F. graminearum isolate was 3ADON chemotype. To date, F. vorosii has only been detected in Hungary on wheat (Toth et al. 2005) and Korea on barley, corn and rice (Lee et al. 2016). This is the first report of F. vorosii in Serbia, which is of great importance, because it indicates the spread of this toxigenic species. Further studies should be focused on determining the distribution, aggressiveness and toxicological profile of F. vorosii.

Identification of Quantitative Trait Loci Associated With Partial Resistance to Fusarium Root Rot and Wilt Caused by Fusarium graminearum in Field Pea.

Fusarium root rot, caused by a complex of Fusarium spp., is a major disease of field pea (Pisum sativum). The development of genetic resistance is the most promising approach to manage the disease, but no pea germplasm has been identified that is completely resistant to root rot. The aim of this study was to detect quantitative trait loci (QTL) conferring partial resistance to root rot and wilting, caused by five fungal isolates representing Fusarium solani, F. avenaceum, F. acuminatum, F. proliferatum, and F. graminearum. Evaluation of the root rot-tolerant cultivar “00-2067” and susceptible cultivar “Reward” was carried out with the five species. There was a significant difference (p < 0.001) between the mean root rot values of the two cultivars inoculated with the F. avenaceum (F4A) and F. graminearum (FG2) isolates. Therefore, in the QTL study, the F8 recombinant inbred line (RIL) population derived from “Reward” × “00-2067” was inoculated in the greenhouse (4 ×) with only F4A and FG2. The parents and F8 population were genotyped using 13.2K single nucleotide polymorphisms (SNPs) and 222 simple sequence repeat (SSR) markers. A significant genotypic effect (p < 0.05) and high heritability (79% to 92.1%) were observed for disease severity, vigor, and plant height following inoculation with F4A and FG2. Significant correlation coefficients were detected among and within all traits. This suggested that a high proportion of the genetic variance was transmitted from the parents to the progeny. However, no significant QTL (LOD > 3) were detected for the RILs inoculated with F4A. In the case of the RILs inoculated with FG2, 5 QTL for root rot severity and 3 QTL each for vigor and plant height were detected. The most stable QTL for plant height (Hgt-Ps3.1) was detected on Chrom5/LGIII. The two most stable QTL for partial resistance to FG2, Fg-Ps4.1, and Fg-Ps4.2 were located in a 15.1-cM and 11.2-cM genomic region, respectively, on Chrom4/LGIV. The most stable QTL for vigor (Vig-Ps4.1) was found in the same region. Twenty-five major and moderate effect digenic epistatic interactions were detected. The identified region on chrom4/LGIV could be important for resistance breeding and marker development.

Analysis of the Fusarium graminearum Species Complex from Gramineous Weeds Near Wheat Fields in Jiangsu Province, China.

Several weed species are known as alternative hosts of the Fusarium graminearum species complex (FGSC), and their epidemiological significance in Fusarium head blight (FHB) has been investigated; however, scant information is available regarding FGSC occurrence in weeds near Chinese wheat fields. To evaluate the potential role of gramineous weeds surrounding wheat fields in FHB, 306 FGSC isolates were obtained from 210 gramineous weed samples in 2018 in Jiangsu Province. Among them, 289 were Fusarium asiaticum, and the remainder were F. graminearum. Trichothecene genotype and mycotoxin analyses revealed that 74.3% of the F. asiaticum isolates were the 3-acetyldeoxynivalenol (3ADON) chemotype, and the remainder were the nivalenol (NIV) chemotype. Additionally, 82.4% of F. graminearum isolates were the 15-acetyldeoxynivalenol (15ADON) chemotype, and the remainder were the NIV chemotype. FHB severity and trichothecene analysis indicated that F. asiaticum isolates with the 3ADON chemotype were more aggressive than those with the NIV chemotype in wheat. 3ADON and NIV chemotypes of F. asiaticum isolated from weeds and wheat showed no significant differences in pathogenicity in wheat. All selected F. asiaticum isolates produced perithecia, with little difference between the 3ADON and NIV chemotypes. These results highlight the epidemiology of the FGSC isolated from weeds near wheat fields, with implications for reducing FHB inoculum in China.

Genome Sequence Analysis of the Fungal Pathogen Fusarium graminearum Using Oxford Nanopore Technology.

Fusarium graminearum is a plant pathogen of global importance which causes not only significant yield loss but also crop spoilage due to mycotoxins that render grain unsafe for human or livestock consumption. Although the full genome of several F. graminearum isolates from different parts of the world have been sequenced, there are no similar studies of isolates originating from China. The current study sought to address this by sequencing the F. graminearum isolate FG-12, which was isolated from the roots of maize seedlings exhibiting typical symptoms of blight growing in the Gansu province, China, using Oxford Nanopore Technology (ONT). The FG-12 isolate was found to have a 35.9 Mb genome comprised of five scaffolds corresponding to the four chromosomes and mitochondrial DNA of the F. graminearum type strain, PH-1. The genome was found to contain an approximately 2.23% repetitive sequence and encode 12,470 predicted genes. Additional bioinformatic analysis identified 437 genes that were predicted to be secreted effectors, one of which was confirmed to trigger a hypersensitive responses (HR) in the leaves of Nicotiana benthamiana during transient expression experiments utilizing agro-infiltration. The F. graminearum FG-12 genome sequence and annotation data produced in the current study provide an extremely useful resource for both intra- and inter-species comparative analyses as well as for gene functional studies, and could greatly advance our understanding of this important plant pathogen.

Fusarium head blight of wheat in India‐variability in pathogens associated and sources of resistance: an overview

During 2019-20 crop season, India harvested record wheat production of 107.19 mt from an area of 30.5 mha thereby registering an all-time high productivity. The most serious fungal diseases which affect wheat production are rusts, spot blotch, Karnal bunt, head scab, powdery mildew, flag smut and loose smut. Recently outbreaks of Fusarium head blight (FHB) or head scab of wheat caused by Fusarium spp., has been reported from Canada, Europe, Asia, Australia and South America. In India, the disease can cause significant yield loss if rain occurs during mid anthesis in the foot hills of Punjab, Himachal Pradesh, Uttarakhand and hilly areas in Tamil Nadu. The Fusarium diseases are likely to increase under the impact of global warming and the fast adoption of reduced tillage practices in the main wheat belt, the north west plains of India. Fusarium graminearum is known to produce mycotoxins which affect human and animal health. Extensive disease surveys undertaken in Himachal Pradesh and Tamil Nadu (Wellington) during 2010–20 revealed the dominance of F. graminearum causing head blight of wheat in India. Pathogenic variation among Fusarium spp./isolates has been studied by inoculating on a set of wheat varieties under artificially inoculated conditions. These studies helped in identifying virulent F. graminearum isolates and their use in evaluating a large number of wheat genotypes for identifying sources of resistance. Genetic variation among F. graminearum isolates have been detected with molecular markers. Since most of the popular cultivars grown in India are susceptible to head scab, there is a need to evaluate a greater number of indigenous and exotic wheat lines for incorporating head scab resistance in popular wheat cultivars. This review provides an overview of the variation in pathogens associated with the disease and resistant sources available for breeding durable FHB resistant wheat varieties.

QTL mapping in Fusarium graminearum identified an allele of FgVe1 involved in reduced aggressiveness

Fusarium graminearum is one of the most frequent causal agents of the Fusarium Head Blight, a cereal disease spread throughout the world, reducing grain production and quality. F. graminearum isolates are genetically and phenotypically highly diverse. Notably, remarkable variations of aggressiveness between isolates have been observed, which could reflect an adaptive potential of this pathogen. In this study, we aimed to characterize the genetic basis of aggressiveness variation observed in an F1 population (n = 94), for which genome sequences of both parental strains are available. Aggressiveness was assessed by a panel of in planta and in vitro proxies during two phenotyping trials including, among others, disease severity and mycotoxin accumulation in wheat spike. One major and single QTL was mapped for all the traits measured, on chromosome I, that explained up to 90% of the variance for disease severity. The confidence interval at the QTL spanned 1.2 Mb and contained 428 genes on the reference genome. Of these, four candidates were selected based on the postulate that a non-synonymous mutation affecting protein function may be responsible for phenotypic differences. Finally, a new mutation was identified and functionally validated in the gene FgVe1, coding for a velvet protein known to be involved in pathogenicity and secondary metabolism production in several fungi.

Population Genetic Structure and Chemotype Diversity of Fusarium graminearum Populations from Wheat in Canada and North Eastern United States.

Fusarium head blight (FHB) is a major disease in wheat causing severe economic losses globally by reducing yield and contaminating grain with mycotoxins. In Canada, Fusarium graminearum is the principal etiological agent of FHB in wheat, producing mainly the trichothecene mycotoxin, deoxynivalenol (DON) and its acetyl derivatives (15-acetyl deoxynivalenol (15ADON) and 3-acetyl deoxynivalenol (3ADON)). Understanding the population biology of F. graminearum such as the genetic variability, as well as mycotoxin chemotype diversity among isolates is important in developing sustainable disease management tools. In this study, 570 F. graminearum isolates collected from commercial wheat crops in five geographic regions in three provinces in Canada in 2018 and 2019 were analyzed for population diversity and structure using 10 variable number of tandem repeats (VNTR) markers. A subset of isolates collected from the north-eastern United States was also included for comparative analysis. About 75% of the isolates collected in the Canadian provinces of Saskatchewan and Manitoba were 3ADON indicating a 6-fold increase in Saskatchewan and a 2.5-fold increase in Manitoba within the past 15 years. All isolates from Ontario and those collected from the United States were 15ADON and isolates had a similar population structure. There was high gene diversity (H = 0.803–0.893) in the F. graminearum populations in all regions. Gene flow was high between Saskatchewan and Manitoba (Nm = 4.971–21.750), indicating no genetic differentiation between these regions. In contrast, less gene flow was observed among the western provinces and Ontario (Nm = 3.829–9.756) and USA isolates ((Nm = 2.803–6.150). However, Bayesian clustering model analyses of trichothecene chemotype subpopulations divided the populations into two clusters, which was correlated with trichothecene types. Additionally, population cluster analysis revealed there was more admixture of isolates among isolates of the 3ADON chemotypes than among the 15ADON chemotype, an observation that could play a role in the increased virulence of F. graminearum. Understanding the population genetic structure and mycotoxin chemotype variations of the pathogen will assist in developing FHB resistant wheat cultivars and in mycotoxin risk assessment in Canada.

Fusarium graminearum isolates obtained from wheat and wild grasses in northeastern New York display comparable range of phenotypes, including virulence on crop hosts

The crop pathogen Fusarium graminearum often colonizes non-cultivated grasses, but the phenotypic variation found in isolates recovered from these hosts has not been thoroughly investigated or compared to that observed in isolates collected from crop hosts. Fusarium graminearum growth, perithecia formation, and virulence on crops (maize seedlings, wheat seedlings, wheat spikes) were measured in laboratory and greenhouse experiments using isolates (n = 24) recovered from three non-cultivated grasses (Bromus inermis, Dactylis glomerata, and Phalaris arundinacea) and winter wheat (Triticum aestivum) found at a single research farm in northeastern New York. While individual isolates varied significantly for all phenotypes measured, grass and wheat derived isolates displayed a comparable range of phenotypic values. Trichothecene genotypes were determined from the TRI12 and TRI1 loci, and mycotoxin production was quantified in mature wheat spikes. Trichothecene genotype and phenotype were largely concordant and were not related to isolate source. These findings support consideration of non-cultivated hosts as sources of diverse pathogen inoculum that may cause crop disease.

Aggressiveness and trichothecene production of Fusarium graminearum isolates from cereals in Serbia

The aim of this study was to assess variations in aggressiveness and trichothecene production of F. graminearum isolates originating from maize, wheat and barley in Serbia. Analyzing F. graminearum isolates (98) obtained from various agroecological conditions of Serbia over the period from 1993 to 2010, using the HPLC method, the following two chemotypes were observed: 3-acetyl-deoxinivalenol (3ADON) and 15-acetyl-deoxinivalenol (15ADON). A great diversity in the production of deoxinivalenol (DON) derivatives was observed. A majority of F. graminearum isolates, regardless of their origin (maize, wheat or barley) belonged to the 15ADON chemotype. The 3ADON chemotype was also detected, but in a significantly smaller number (13/98) samples, compared to the 15ADON chemotype (85/98). None of the tested isolates belonged to the NIV chemotype. The examined isolates showed different pathogenicity on barley leaf, wheat class and maize ears. The average pathogenicity of the tested isolates was the highest on barley leaf. It was observed that isolates originating from wheat had the highest average daily increase in mycelium growth rate (27.37 mm). Statistical analysis of the obtained results for mycotoxins synthesis showed that there was a highly significant statistical correlation between the production potentials of total DON, 3ADON and 15ADON in F. graminearum isolates belonging to various chemotypes. However, there was no statistically significant correlation between the aggressiveness of isolates and the production of total DON in isolates belonging to 3ADON and 15ADON chemotypes.

Multifaceted Insights on Fusarium Head Blight in Small Grains in Pennsylvania

Fusarium head blight (FHB) is a serious disease of small-grain cereals that causes economic losses due to both yield reduction and mycotoxin contamination worldwide. To optimize the regional management of the disease, knowledge of risk factors associated with FHB outbreaks and mycotoxin accumulation are essential steps. Therefore, a 2-year survey was conducted during the summers of 2018 and 2019, in which naturally FHB-affected spikes from different hosts were collected across the major cereal-producing regions of Pennsylvania (South, Central, and North). FHB severity (%) data were recorded from each field. Furthermore, a collection of 307 Fusarium graminearum isolates was used to investigate specific components of the pathogen biology, such as the composition of the trichothecene genotype, saprophytic and pathogenic fitness, and sensitivity to triazole-based fungicides. Our results confirm that FHB is an important disease in Pennsylvania, and the risk of disease epidemics may be impacted by both the year and the location. Overall, the regional population of F. graminearum causing FHB in Pennsylvania is the 15ADON genotype. Based on in vitro and in vivo experiments, F. graminearum populations obtained from three distinct small-grain management regions could not be differentiated for the majority of fitness traits examined. All isolates were sensitive to tebuconazole and metconazole fungicides in vitro. Overall, this new knowledge can help shed light on the relative importance of FHB epidemics in Pennsylvania and provide directions for monitoring the sustainability of the integrated strategies used to manage FHB and mycotoxin accumulation.

In vitro effect of some commercial fungicides on mycelial growth of Fusarium species causing maize ear rot disease in China

Fusarium ear rot is an important disease of maize and requires several fungicide treatments to achieve satisfactory control in China. The extensive use of common fungicides to control this disease has caused fungicides resistance of pathogens. In this study, we tested the effect of different commercial fungicides on mycelial growth of Fusarium graminearum and Fusarium oxysporum isolates collected from different fields in the Jilin Province of China in 2014. The effect of concentration on mycelial growth varied significantly (p < 0.05) between tested commercial fungicides. Our results showed that among the 10 tested commercial fungicides, prochloraz and polyoxin-D highly reduced the mycelial growth of Fusarium graminearum by 3.4 cm and 4.1 cm, respectively as compared to other fungicides at a concentration of 0.1 mg/L. Moreover, a 0.1 mg/L concentration of polyoxin-D, tebuconazole, fosetyl-Al, fludioxonil, azoxystrobin, and carbendazim were also highly effective to decrease the mycelial growth of Fusarium oxysporum with 3.1 cm, 3.1 cm, 3.4 cm, 3.8 cm, and 4.4 cm as compared to other fungicides at the same concentration. These results will provide useful information to select suitable fungicides for management and control of maize ear rot disease caused by Fusarium graminearum and Fusarium oxysporum and further increase our understanding of the effects of different fungicides concentrations on Fusarium graminearum and Fusarium oxysporum.

Genetic diversity of Fusarium meridionale, F. austroamericanum, and F. graminearum isolates associated with Fusarium head blight of wheat in Brazil

One of the biggest challenges of wheat production worldwide is to overcome fungal diseases, and among these is Fusarium head blight (FHB) caused mainly by the Fusarium graminearum species complex (FGSC). The occurrence of FHB can lead to contamination of grains with mycotoxins, which are harmful to human and animal health. In South America, in addition to F. graminearum sensu stricto (F. graminearum), which is the most common causal agent of FHB worldwide, F. meridionale and F. austroamericanum have also been found in wheat fields. Special attention should be paid to F. meridionale because it produces the trichothecene mycotoxin nivalenol, which has potentially higher levels of toxicity when compared with that of other trichothecene produced by the FGSC. Knowledge of the diversity and genetic structure of populations of pathogens can assist in understanding pathogen survival in the face of host genetic resistance, crop rotation, and management with fungicides. In this study, we used 10 inter-simple sequence repeat (ISSR) primers to estimate the variability, diversity, and genetic structure of populations of F. graminearum, F. meridionale, and F. austroamericanum co-occurring in wheat fields in Parana State, Brazil. The population of F. graminearum showed the greatest genetic variability according to its polymorphism (P = 86.61%), Nei’s genetic diversity (h = 0.28), and Shannon diversity (I = 0.43) indices as compared with that of the populations of F. meridionale (P = 75.89%, h = 0.23, I = 0.36) and F. austroamericanum (P = 67.86%, h = 0.22, I = 0.33). The dendrogram, principal coordinate analysis, Bayesian analysis (K = 4), and the differentiation index (GST = 0.27) showed very high structure and, consequently, high species differentiation. The overall analysis of our data indicates high variability and genetic structure of the studied populations. This genetic condition guarantees high resilience of these species and could make it difficult to obtain wheat cultivars with good resistance to FHB, as well as may cause chemical control to be less effective.

Biological Characteristics and Molecular Mechanisms of Fludioxonil Resistance in Fusarium graminearum in China.

Fusarium graminearum is the primary causal agent of Fusarium head blight (FHB) of wheat. The phenylpyrrole fungicide fludioxonil is not currently registered for the management of FHB in China. The current study assessed the fludioxonil sensitivity of a total of 53 F. graminearum isolates collected from the six most important wheat-growing provinces of China during 2018 and 2019. The baseline fludioxonil sensitivity distribution indicated that all of the isolates were sensitive, exhibiting a unimodal cure with a mean effective concentration for 50% inhibition value of 0.13 ± 0.12 μg/ml (standard deviation). Five fludioxonil-resistant mutants were subsequently induced by exposure to fludioxonil under laboratory conditions. Ten successive rounds of subculture in the absence of the selection pressure indicated that the mutation was stably inherited. However, the fludioxonil-resistant mutants were found to have reduced pathogenicity, higher glycerol accumulation, and higher osmotic sensitivity than the parental wild-type isolates, indicating that there was a fitness cost associated with fludioxonil resistance. In addition, the study also found a positive cross resistance between fludioxonil, procymidone, and iprodione, but not with other fungicides such as boscalid, carbendazim, tebuconazole, and fluazinam. Sequence analysis of four candidate target genes (FgOs1, FgOs2, FgOs4, and FgOs5) revealed that the HBXT2R mutant contained two point mutations that resulted in amino acid changes at K223T and K415R in its FgOs1 protein, and one point mutation at residue 520 of its FgOs5 protein that resulted in a premature stop codon. Similarly, the three other mutants contained point mutations that resulted in changes at the K192R, K293R, and K411R residues of the FgOs5 protein but none in the FgOs2 and FgOs4 genes. However, it is important to point out that the FgOs2 and FgOs4 expression of all the fludioxonil-resistant mutants was significantly (P < 0.05) downregulated compared with the sensitive isolates (except for the SQ1-2 isolate). It was also found that one of the resistant mutants did not have changes in any of the sequenced target genes, indicating that an alternative mechanism could also lead to fludioxonil resistance.

Baseline sensitivity and control efficacy of epoxiconazole against Fusarium graminearum in Henan Province, China

Fusarium head blight (FHB), caused by Fusarium graminearum species complex (FGSC) is one of the most destructive wheat diseases worldwide. F. graminearum is the dominant pathogen of FHB in Henan Province. Epoxiconazole is a demethylation inhibitor (DMI) fungicide, and is the main fungicide for controlling FHB in China. In this study, 118 F. graminearum isolates were collected from different regions of Henan Province in 2016 and 2017. The sensitivity of these F. graminearum isolates to epoxiconazole was determined by the method of mycelial growth inhibition. The results showed that the EC50 values range of epoxiconazole to the tested F. graminearum isolates was 0.0196 to 0.5708 μg ml−1, and the mean EC50 value was 0.2178 ± 0.1178 μg ml−1 (mean ± SD). The sensitivity frequency distribution of these F. graminearum isolates to epoxiconazole was a continuous single peak curve, and no isolates resistant to epoxiconazole were found in Henan Province, China. The field control efficacy of epoxiconazole against F. graminearum was evaluated and the results showed that epoxiconazole had a significantly higher control efficacy on FHB, compared to the control fungicide carbendazim. The thousand grain weight of all the fungicide treatments was significantly higher than water control (without fungicide). This study showed that the DMI fungicide epoxiconazole has high activity and field control efficacy on F. graminearum, and can effectively control the prevalence of FHB.

Analysis of Fusarium graminearum Species Complex from Freshly Harvested Rice in Jiangsu Province (China).

Members of Fusarium graminearum species complex (FGSC) are the major pathogens that cause Fusarium head blight (FHB) in cereals worldwide. Symptoms of FHB on rice, including dark staining or browning of rice glumes, were recently observed in Jiangsu Province, China. To improve our understanding of the pathogens involved, 201 FGSC isolates were obtained from freshly harvested rice samples and identified by phylogenetic analyses. Among the 201 FGSC isolates, 196 were F. asiaticum and the remaining 5 were F. graminearum. Trichothecene chemotype and chemical analyses showed that 68.4% of the F. asiaticum isolates were the 3-acetyldeoxynivalenol (3ADON) chemotype and the remainder were the nivalenol (NIV) chemotype. All of the F. graminearum isolates were the 15-acetyldeoxynivalenol chemotype. Pathogenicity assays showed that both the 3ADON and NIV chemotypes of F. asiaticum could infect wheat and rice spikes. FHB severity and trichothecene toxin analysis revealed that F. asiaticum with the NIV chemotype was less aggressive than that with the 3ADON chemotype in wheat, while the NIV-producing strains were more virulent than the 3ADON-producing strains in rice. F. asiaticum isolates with different chemotypes did not show significant differences in mycelial growth, sporulation, conidial dimensions, or perithecial production. These findings would provide useful information for developing management strategies for the control of FHB in China.