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1.
Fusarium head blight (FHB) in small grain cereals is primarily caused by the members of the Fusarium graminearum species complex. These produce mycotoxins in infected grains, primarily deoxynivalenol (DON); acetylated derivatives of DON, 3‐acetyl‐DON (3‐ADON) and 15‐acetyl‐DON (15‐ADON); and nivalenol (NIV). This study reports the isolation of Fusarium cerealis in infected winter wheat heads for the first time in Canada. A phylogenetic analysis based on the TRI101 gene and F. graminearum species‐specific primers revealed two species of Fusarium: F. graminearum sensu stricto (127 isolates) and F. cerealis (five isolates). Chemotype determination based on the TRI3 gene revealed that 65% of the isolates were 3‐ADON, 31% were 15‐ADON and 4% were NIV producers. All the F. cerealis isolates were of NIV chemotype. Fusarium cerealis isolates can often be misidentified as F. graminearum as the morphological characteristics are similar. Although the cultural and macroconidial characteristics of F. graminearum and F. cerealis isolates were similar, the aggressiveness of these isolates on susceptible wheat cultivar Roblin and moderately resistant cultivar Carberry differed significantly. The F. graminearum 3‐ADON isolates were most aggressive, followed by F. graminearum 15‐ADON and F. cerealis NIV isolates. The findings from this study confirm the continuous shift of chemotypes from 15‐ADON to 3‐ADON in North America. In Canada, the presence of NIV is limited to barley samples and the discovery of NIV‐producing F. cerealis species in Canadian wheat fields may pose a serious concern to the Canadian wheat industry in the future.  相似文献   

2.
This study aimed to assess the extent and distribution of Fusarium graminearum species complex (FGSC) diversity in rice seeds produced in southern Brazil. Four species and two trichothecene genotypes were detected among 89 FGSC isolates, based on a multilocus genotyping assay: F. asiaticum (69·6%) with the nivalenol (NIV) genotype, F. graminearum (14·6%) with the 15‐acetyldeoxynivalenol (ADON) genotype, and F. cortaderiae (14·6%) and F. meridionale (1·1%), both with the NIV genotype. Seven selected F. asiaticum isolates from rice produced NIV in rice‐based substrate in vitro, at levels ranging from 4·7 to 84·1 μg g?1. Similarly, two F. graminearum isolates from rice produced mainly 15‐ADON (c. 15–41 μg g?1) and a smaller amount of 3‐ADON (c. 6–12 μg g?1). One F. meridionale and two F. cortaderiae isolates did not produce detectable levels of trichothecenes. Two F. asiaticum isolates from rice and two from wheat (from a previous study), and one F. graminearum isolate from wheat, were pathogenic to both crops at various levels of aggressiveness based on measures of disease severity in wheat spikes and rice kernel infection in a greenhouse assay. Fusarium asiaticum and the reference F. graminearum isolate from wheat produced NIV, and deoxynivalenol and acetylates, respectively, in the kernels of inoculated wheat heads. No trichothecene was produced in kernels from inoculated rice panicles by any of the isolates. These findings constitute the first report of FGSC composition in rice outside Asia, and confirm the dominance of F. asiaticum in rice agroecosystems.  相似文献   

3.
Members of the Fusarium graminearum species complex (FGSC), such as F. graminearum and F. asiaticum, are the main cause of fusarium head blight (FHB) of wheat and barley worldwide. In this study, 117 FGSC isolates obtained from commercial barley grain produced in Argentina (n = 43 isolates), Brazil (n = 35), and Uruguay (n = 39) were identified to species and trichothecene genotypes, and analysed using amplified fragment length polymorphism (AFLP) and sequence‐related amplified polymorphism (SRAP) markers. In addition, reductase (RED) and trichothecene 3‐O‐acetyltransferase (Tri101) were sequenced for a subset of 24 isolates. The majority of the isolates (n = 103) were identified as F. graminearum, which was the only species found in Argentina. In Uruguay, only one F. cortaderiae isolate was found among F. graminearum isolates. In Brazil, F. graminearum also dominated the collection (22/35), followed by F. meridionale (8/35), F. asiaticum (2/35), F. cortaderiae (2/35) and F. austroamericanum (1/35). Species were structured by trichothecene genotype: all F. graminearum were of the 15‐acetyldeoxynivalenol (ADON), F. meridionale, F. asiaticum and F. cortaderiae were of the nivalenol (NIV), and F. austroamericanum was of the 3‐ADON genotype. Both AFLP and SRAP data showed high levels of genetic variability, which was higher within than among countries. Isolates were not structured by country of origin. SRAP analysis grouped F. graminearum in a separate cluster from the other species within the complex. However, AFLP analysis failed to resolve the species into distinct clades with partial clustering of F. meridionale, F. austroamericanum, F. asiaticum and F. graminearum isolates.  相似文献   

4.
Fusarium head blight (FHB) and deoxynivalenol (DON) mycotoxin produced by Fusarium graminearum reduce barley yield and quality worldwide. Hundreds of quantitative trait loci (QTLs) have been identified in wheat and barley but their functions are largely unknown. Metabolic profiling was applied to better understand the mechanisms of resistance and to identify potential FHB resistance biomarker metabolites in barley. Four FHB resistant (H15-2, H148-3, H203-2 and H379-2) and one susceptible (H97-2), two-row, purple, doubled-haploid (DH) lines of barley were inoculated with either the pathogen or mock-solution. The disease severity quantified as the area under the disease progress curve (AUDPC) significantly varied between the resistant and susceptible genotypes, but not among the resistant genotypes. Neither the amount of DON nor the detoxified product, proportion of total DON, was significant among lines. The resistance related (RR, higher in abundance in resistant than in susceptible) metabolites varied in numbers and fold changes among the DH resistant lines. A total of 144 RR constitutive (RRC) and 167 RR induced (RRI) metabolites were selected, of which 39 and 37, respectively, were putatively identified. These RR metabolites mainly belonged to six chemical groups: phenylpropanoids, hydroxycinnamic acid amides, flavonoids, fatty acids, terpenoids, and alkaloids. The specific RR metabolites identified in each DH line, the possible mechanisms of resistance in each and their use as potential biomarkers are discussed.  相似文献   

5.
Y. You  Y. Shirako 《Plant pathology》2013,62(1):226-232
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6.
Studies were conducted to explain the relative success of ‘Dickeya solani’, a genetic clade of Dickeya biovar 3 and a blackleg‐causing organism that, after recent introduction, has spread rapidly in seed potato production in Europe to the extent that it is now more frequently detected than D. dianthicola. In vitro experiments showed that both species were motile, had comparable siderophore production and pectinolytic activity, and that there was no antagonism between them when growing. Both ‘D. solani’ and biovar 1 and biovar 7 of D. dianthicola rotted tuber tissue when inoculated at a low density of 103 CFU mL?1. In an agar overlay assay, D. dianthicola was susceptible to 80% of saprophytic bacteria isolated from tuber extracts, whereas ‘D. solani’ was susceptible to only 31%, suggesting that ‘D. solani’ could be a stronger competitor in the potato ecosystem. In greenhouse experiments at high temperatures (28°C), roots were more rapidly colonized by ‘D. solani’ than by biovar 1 or 7 of D. dianthicola and at 30 days after inoculation higher densities of ‘D. solani’ were found in stolons and progeny tubers. In co‐inoculated plants, fluorescent protein (GFP or DsRed)‐tagged ‘D. solani’ outcompeted D. dianthicola in plants grown from vacuum‐infiltrated tubers. In 3 years of field studies in the Netherlands with D. dianthicola and ‘D. solani’, disease incidence varied greatly annually and with strain. In summary, ‘D. solani’ possesses features which allow more efficient plant colonization than D. dianthicola at high temperatures. In temperate climates, however, tuber infections with ‘D. solani’ will not necessarily result in a higher disease incidence than infections with D. dianthicola, but latent seed infection could be more prevalent.  相似文献   

7.
The aim of the present study was to investigate the effects of the phytotoxin fusaric acid (FA) on the biocontrol traits of two biocontrol strains Paenibacillus polymyxa WR‐2 and SQR‐21. The results showed that the growth of both WR‐2 and SQR‐21 decreased with increasing FA concentration, and at 70 and 80 μg mL?1 FA, respectively, the strains were unable to grow. The biocontrol traits of both strains were negatively affected by FA concentration higher than 2·5 μg mL?1. However, at 2·5 μg mL?1 FA, biofilm formation and root colonization were not affected and there was even a positive effect on the production of spores and hydrolytic enzymes (protease and β‐l,3‐glucanase). The production of fusaricidin‐type antifungal compounds was increased with an increase in FA concentration up to 50 and 60 μg mL?1 for WR‐2 and SQR‐21, respectively. The production of antifungal volatile organic compounds by WR‐2 and SQR‐21 was increased only at 2·5 μg mL?1 FA. The effect of FA on the overall metabolic activity of WR‐2 and SQR‐21 was also determined. This study will help to understand the response of P. polymyxa strains to FA and will help to improve their biocontrol efficiency.  相似文献   

8.
White mould (Sclerotinia sclerotiorum) is a destructive disease of soybean worldwide. However, little is known of its impact on soybean production in Brazil. A meta‐analytic approach was used to assess the relationship between disease incidence and soybean yield (35 trials) and between incidence and sclerotia production (29 trials) in experiments conducted in 14 locations across four seasons. Region, site elevation and season included as moderators in random‐effects and random‐coefficients models did not significantly explain the variability in the slopes of the incidence–yield relationship. The Pearson's r, obtained from back‐transforming the Fisher's Z estimated by an overall random‐effects model, showed that incidence of white mould was moderately and negatively correlated with yield (r = ?0.76, P < 0.0001). A random‐coefficients model estimated a slope of ?17.2 kg ha?1%?1, for a mean attainable yield of 3455 kg ha?1, indicating that a 10% increase in white mould incidence would result in a mean yield reduction of 172 kg ha?1. White mould incidence and production of sclerotia were strongly and positively correlated (r = 0.85, P < 0.0001). For every 10% increase in white mould incidence, 1 kg ha?1 of sclerotia was produced. The relationship between disease incidence and production of sclerotia was stronger in southern regions and at higher elevation. In the absence of management, economic losses associated with white mould epidemics, assuming 43% incidence in 22% of the soybean area, were estimated at approximately US $1.47 billion annually within Brazil.  相似文献   

9.
The effects of herbicide dose on rice‐weed competition were investigated to develop a combined model, which can be utilised to estimate an optimum herbicide dose for a given weed density in paddy rice cultivation. Field studies were conducted in Suwon for rice‐Echinochloa crus‐galli competition and Iksan for rice‐Eleocharis kuroguwai during 2007. The competitive effect of the weeds E. crus‐galli and E. kuroguwai decreased with increasing doses of flucetosulfuron and azimsulfuron, respectively, in the same manner as the standard dose–response curve. The combination of the rectangular hyperbolic model and the standard dose–response curve adequately described the complex effects of herbicide dose and weed competition on rice yield. Parameter estimates were used with the model to predict rice yield and estimate the doses of flucetosulfuron and azimsulfuron required to restrict rice yield loss caused by E. crus‐galli and E. kuroguwai, respectively, to an acceptable level. For a rice yield of 5.0 t ha?1, the model recommended flucetosulfuron doses of 8.7, 13.4 and 20.1 g a.i. ha?1 when infested with E. crus‐galli at 12, 24 and 48 plants m?2 respectively. For a rice yield of 5.2 t ha?1, the model recommended azimsulfuron doses of 3.9, 7.5 and 12.6 g a.i. ha?1 when infested with E. kuroguwai at 24, 48 and 96 plants m?2 respectively. The theoretical outputs of the combined model appear robust and indicate there are opportunities for reduced herbicide use in the field. These now require evaluation under field conditions.  相似文献   

10.
Eutypa lata is the causal agent of eutypa dieback, a highly damaging trunk disease affecting all grape‐growing areas, with currently neither an efficient curative treatment nor an early non‐destructive diagnostic method. The present work was carried out to discover grapevine genes expressed in response to the presence of E. lata that could be useful to develop an early (before visible foliar symptoms) and non‐destructive (using grapevine leaves) diagnostic tool. Microarray analyses were carried out from (i) infected plants showing characteristic E. lata foliar and vascular symptoms and positive pathogen recovery from vascular lesions (S+R+), (ii) infected plants showing no symptoms (S?R+), and (iii) symptomless plants with negative pathogen recovery (S?R?). Vineyard and greenhouse‐grown plants, naturally or artificially infected respectively, and uninoculated controls were characterized and leaf RNA was hybridized with 15k operon grapevine oligonucleotide microarrays. Among the grapevine genes differentially expressed between S?R+ and S?R? plants in greenhouse and vineyard conditions, 10 were highlighted as robust candidate genes for diagnosis: seven were specifically involved in response to infection and three were associated with symptom absence. Five were confirmed to be effective diagnostic marker genes usable in a qRT‐PCR‐based test performed on RNA extracted from grapevine leaves cultivated in either greenhouse or vineyard conditions. Furthermore, their expression profiles in response to infection with E. lata or other major grapevine fungi (Erysiphe necator, Plasmopara viticola, Botrytis cinerea) could be distinguished. The usefulness of these genes to develop an early and non‐destructive method for diagnosis of E. lata infection is discussed with regard to the advantages and drawbacks of previous E. lata diagnostic studies.  相似文献   

11.
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12.
Quorum sensing in Gram‐negative bacteria is regulated by diffusible signal molecules called N‐acyl‐l ‐homoserine lactones (AHLs). These molecules are degraded by lactonases. In this study, six Bacillus simplex isolates were characterized and identified as a new quorum‐quenching species of Bacillus. An aiiA gene encoding an AHL‐lactonase was identified based on evidence that: (i) it showed high homology with other aiiA genes of Bacillus sp.; (ii) the deduced amino acid sequence contained two conserved regions, 104SHLHFDH111 and 165TPGHTPGH173, characteristic of the metallo‐β‐lactamase superfamily; and (iii) the protein had zinc‐dependent AHL‐degrading activity. Additionally, the expression of the aiiA gene was significantly up‐regulated by 3‐oxo‐AHL. The AHL‐lactonase inhibited multiplication of the 3‐oxo‐C6‐AHL‐producing plant pathogen Erwinia amylovora sy69 both in vitro and in planta. The results provide support for the use of the quorum‐quenching functionality of B. simplex in the integrated control of the devastating fire blight pathogen.  相似文献   

13.
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14.
Potato early dying (PED) is a disease complex primarily caused by the fungus Verticillium dahliae. Pectolytic bacteria in the genus Pectobacterium can also cause PED symptoms as well as aerial stem rot (ASR) of potato. Both pathogens can be present in potato production settings, but it is not entirely clear if additive or synergistic interactions occur during co‐infection of potato. The objective of this study was to determine if co‐infection by V. dahliae and Pectobacterium results in greater PED or ASR severity using a greenhouse assay and quantitative real‐time PCR to quantify pathogen levels in planta. PED symptoms caused by Pectobacterium carotovorum subsp. carotovorum isolate Ec101 or V. dahliae isolate 653 alone included wilt, chlorosis and senescence and were nearly indistinguishable. Pectobacterium wasabiae isolate PwO405 caused ASR symptoms including water‐soaked lesions and necrosis. Greater Pectobacterium levels were detected in plants inoculated with PwO405 compared to Ec101, suggesting that ASR can result in high Pectobacterium populations in potato stems. Significant additive or synergistic effects were not observed following co‐inoculation with these strains of V. dahliae and Pectobacterium. However, infection coefficients of V. dahliae and Ec101 were higher and premature senescence was greater in plants co‐inoculated with both pathogens compared to either pathogen alone in both trials, and V. dahliae levels were greater in basal stems of plants co‐inoculated with either Pectobacterium isolate. Overall, these results indicate that although co‐infection by Pectobacterium and V. dahliae does not always result in significant additive or synergistic interactions in potato, co‐infection can increase PED severity.  相似文献   

15.
Fusarium head blight (FHB), caused principally by Gibberella zeae (Fusarium graminearum), is a devastating disease of small grains such as wheat and barley worldwide. Grain infected with G. zeae may be contaminated with trichothecene mycotoxins such as deoxynivalenol (DON) and nivalenol (NIV). Strains of G. zeae that produce DON may also produce acetylated derivatives of DON: 3‐acetyl‐DON (3‐ADON) and 15‐acetyl‐DON (15‐ADON). Gradients (clines) of 3‐ADON genotypes in Canada have raised questions about the distribution of G. zeae trichothecene genotypes in wheat fields in the eastern USA. Tri3 and Tri12 genotypes were evaluated in 998 isolates of G. zeae collected from 39 winter wheat fields in New York (NY), Pennsylvania (PA), Maryland (MD), Virginia (VA), Kentucky (KY) and North Carolina (NC). Ninety‐two percent (919/998) of the isolates were 15‐ADON, 7% (69/998) were 3‐ADON, and 1% (10/998) was NIV. A phylogenetic analysis based on portions of three genes (PHO, RED and URA) from 23 isolates revealed two species of Fusarium (F. graminearum sensu stricto and one isolate of F. cerealis (synonym F. crookwellense)). An increasing trend of 3‐ADON genotypes was observed from NC (south) to NY (north). Punctuated episodes of atmospheric transport may favour a higher frequency of 3‐ADON genotypes in the northeastern USA, near Canada, compared with the mid‐Atlantic states. Discoveries of the NIV genotype in NY and NC indicate the need for more intensive sampling in the surrounding regions.  相似文献   

16.
Fusarium culmorum (Fc) and F. graminearum (Fg) belong to the predominant causal agents of fusarium crown and root rot (FCR) in wheat. While many studies have been done to investigate crown rot, including stem base infection, root colonization and mycotoxin production associated with root rot is not well understood. In this study the impact of mycotoxins on the colonization of wheat roots and stem bases was analysed by using Fc and Fg isolates that varied in both quantity and types of trichothecenes they produce. Seedling inoculations in growth chambers with a high deoxynivalenol (DON)- and 3-acetyldeoxynivalenol (3ADON)-producing isolate led to more severe symptoms and 20-times greater colonization of the stem base, as measured by Fc DNA accumulation, than isolates that produced less DON/3ADON. In contrast to stem base colonization, in vitro inoculations of roots with a Tri5 deletion mutant deficient in Fg trichothecene production led to three-times higher colonization than the wildtype. Furthermore, an Fc isolate that produced low levels of zearalenone resulted in twice the level of colonization of a high DON/3ADON-producing isolate included in the study. When root inoculation with a low DON/3ADON-producing Fc isolate was supplemented with exogenous DON, DON production decreased by more than half per unit weight of Fc DNA, and root colonization doubled compared to the untreated control. Therefore, in contrast to its potential role as an aggressiveness factor in stem base infection, trichothecene production by Fc and Fg is detrimental to the early stages of wheat root colonization in FCR.  相似文献   

17.
Fusarium pseudograminearum, F. culmorum and F. graminearum are the most important fusarium crown rot (FCR) causal agents. They have the common ability to biosynthesize deoxynivalenol (DON). To elucidate the behaviour of each of the three species, a comparative study was carried out to investigate symptom progression, fungal systemic growth and translocation of DON following stem base inoculation of soft wheat. FCR symptoms were mainly localized in the inoculated area, which extended up to the second node for all inoculated species. Only the most aggressive strains caused symptoms up to the third node. Real‐time quantitative PCR showed that fungal colonization reached the third node for all the tested species, but a low percentage of plants showed colonization above the third node following inoculation with the most aggressive strains. Fungal growth was detected in symptomless tissues but none of the three species was able to colonize as far as the head tissues. However, even if the pathogens were not detected in the heads, DON was detected in head tissues of the plants inoculated with the most aggressive strains. These results demonstrate that F. pseudograminearum, F. culmorum and F. graminearum, under the same experimental conditions, follow a similar pattern of symptom progression, fungal colonization and DON translocation after stem base infection. Differences in the extent of symptoms, fungal colonization and mycotoxin distribution were mainly attributable to strain aggressiveness. These findings provide comparative information on the events following infection of the stem base of wheat by three of the most important FCR casual agents.  相似文献   

18.
Resistance to carbendazim of Fusarium graminearum is conferred by point mutation in the β2‐tubulin gene that plays an important role in spindle assembly. The spindle assembly checkpoint is a cellular surveillance system that is critical for maintaining genomic stability. Predicted protein Mad2‐ and Bub1‐encoding genes in F. graminearum (FgMad2 and FgBub1) were isolated and characterized. There was no difference in FgMad2 and FgBub1 expression levels between carbendazim‐sensitive and ‐resistant strains; however, after carbendazim treatment FgMad2 expression increased while FgBub1 expression stayed the same. Both the FgMad2 and FgBub1 deletion mutants became more sensitive to carbendazim. The FgMad2 deletion mutants grew more slowly, produced fewer conidia and both hyphae and conidia were malformed. Conversely, deletion of FgBub1 had no effect on fungal development other than a reduction in conidia production. FgMad2 deletion mutants exhibited a severe decrease in perithecia production and pathogenicity along with a down‐regulation of trichothecene production, whereas FgBub1 deletion mutants exhibited only a slight reduction in perithecia production and was accompanied by a twofold increase in trichothecene production. Overall, the results indicate that both FgMad2 and FgBub1 are involved in carbendazim resistance and trichothecene biosynthesis, and FgMad2 plays an important role in fungal development in F. graminearum.  相似文献   

19.
Pyrenophora tritici‐repentis (Ptr) is a destructive fungal pathogen of wheat worldwide. In addition to wheat, Ptr has been isolated from various other hosts in the family Poaceae, yet the nature of its interaction with those hosts is unknown. The Ptr–barley relationship was explored and the existence of a specific interaction between Ptr and barley is described for the first time; symptom development on several barley genotypes was evaluated in bioassays and by toxin infiltration into barley leaves. Ptr ToxB‐producing isolates of the fungus were able to cause significant damage when inoculated onto certain barley genotypes, and Ptr ToxB was able to induce chlorosis in a highly selective manner when infiltrated into those same genotypes. Ptr–barley specificity is subtle and can break with slight changes in temperature after infection. To understand the infection process in barley, a cytological analysis and in planta fungal biomass estimation using quantitative PCR were performed. The fungus penetrates through the host epidermal cells and advances to colonize the mesophyll layer intercellularly, with the infection process on barley closely resembling that on wheat. Here, evidence is provided for a specific interaction between barley and Ptr, expanding understanding of Ptr host specificity and breaking the assumption that the highest level of specificity seen with Ptr is restricted to particular genotypes of the wheat host.  相似文献   

20.
Combined analyses of the natural occurrence of fusarium head blight (FHB), mycotoxins and mycotoxin‐producing isolates of Fusarium spp. in fields of wheat revealed FHB epidemics in 12 of 14 regions in Hubei in 2009. Mycotoxin contamination ranged from 0·59 to 15·28 μg g?1 in grains. Of the causal agents associated with symptoms of FHB, 84% were Fusarium asiaticum and 9·5% were Fusarium graminearum, while the remaining 6·5% were other Fusarium species. Genetic chemotyping demonstrated that F. asiaticum comprised deoxynivalenol (DON), 3‐acetyldeoxynivalenol (3‐AcDON), 15‐acetyldeoxynivalenol (15‐AcDON) and nivalenol (NIV) producers, whereas F. graminearum only included DON and 15‐AcDON producers. Compared with the chemotype patterns in 1999, there appeared to be a modest shift towards 3‐AcDON chemotypes in field populations during the following decade. However, isolates genetically chemotyped as 3‐AcDON were present in all regions, whereas the chemical 3‐AcDON was only detected in three of the 14 regions where 3‐AcDON accounted for 15–20% of the DON and acetylated forms. NIV mycotoxins were detected in seven regions, six of which also yielded NIV chemotypes. The number of genetic 3‐AcDON producers was positively correlated with amounts of total mycotoxins (DON, NIV and acetylated forms) or DON in wheat grains. Chemical analyses of wheat grains and rice cultures inoculated with different isolates from the fields confirmed their genetic chemotypes and revealed a preferential biosynthesis of 3‐AcDON and 4‐AcNIV in rice. These findings suggest the importance of chemotyping coupled with species identification for improved prediction of mycotoxin contamination in wheat.  相似文献   

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