The effect of a mixture of seed-borne Microdochium nivale var. majus and Microdochium nivale var. nivale infection on Fusarium seedling blight severity and subsequent stem colonisation and growth of winter wheat in pot experiments

Greenhouse experiments were conducted in order to determine the impact of seed-borne Microdochium nivale var. nivale and var. majus inoculum, and seed treatment with a carboxin+thiram mixture, on the development of seedling blight, and on subsequent stem colonisation and growth of winter wheat (cv. Cadenza). Experiments were conducted at temperatures favourable (3°C) and unfavourable (22°C) to M. nivale. Seed-borne inoculum resulted in seedling blight symptom development when plants were grown at 3°C, but not when plants were grown at 22°C. For seedlings grown at 3°C, plants arising from heavily blighted seedlings developed more severe symptoms of stem colonisation, when compared with those arising from seedlings from carboxin+thiram treated seeds. In addition, the vigour of such plants (assessed by determining the number of tillers and ears per plant, stem length, green leaf area, dry weight and yield) was also significantly lower than for plants arising from carboxin+thiram treated seeds. Microdochium nivale var. majus and var. nivale appeared to have little effect on plant vigour from seedlings grown at 22°C. This is the first recorded incidence of seedling blight affecting subsequent plant growth. Microdochium nivale var. majus and var. nivale stem colonisation increased from growth stage (GS) 40–49 to harvest in plants raised from seedlings grown at both temperatures. Microdochium nivale var. majus and var. nivale were isolated from the second node at GS 40–49 and the third node at harvest of plants from seedlings grown at 3°C. For plants from seedlings raised at 22°C, M. nivale var. majus and var. nivale were isolated from the first node at GS 40–49 and the second node at harvest. Carboxin+thiram seed treatment decreased the extent and severity of stem colonisation on plants from seedlings grown at 22°C.     

Trichothecene production is detrimental to early root colonization by Fusarium culmorum and F. graminearum in fusarium crown and root rot of wheat

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.     

Relationship between brown foot rot and DNA of Microdochium nivale, determined by quantitative PCR, in stem bases of winter wheat

Relationships between the incidence and severity of brown foot rot and of pathogenic fungi, determined by diagnostic and quantitative PCR, were investigated during the growth of nine winter wheat crops in three cropping seasons. Microdochium nivale vars nivale and majus were the only brown foot rot pathogens present in significant amounts. Relationships between disease symptoms and amounts of pathogen DNA were often weak in early spring (when shoot-base symptoms are usually most difficult to ascribe to particular pathogens by visual examination) because of indistinct symptoms and small amounts of pathogen. Relationships were strongest during stem elongation. The amount of M. nivale in the tissues tended to decline in the summer as the plants matured, apparently disappearing partially from necrotic lesions to which it contributed, resulting in a weakened relationship between symptoms and pathogen DNA. Regression analyses of brown foot rot on amounts of M. nivale DNA for different wheat cultivars generally produced lines with similar slopes but were often most significant for the cultivar with most eyespot resistance (i.e. with least confounding eyespot) or most apparently genuine brown foot rot. DNA of Fusarium spp. was rarely present in amounts sufficient to quantify.     

Comparative population structure and trichothecene mycotoxin profiling of Fusarium graminearum from corn and wheat in Ontario,central Canada

Fusarium graminearum causes fusarium head blight (FHB) of wheat and gibberella ear rot (GER) of corn in Canada and also contaminates grains with trichothecene mycotoxins. Very little is known about trichothecene diversity and population structure of the fungus from corn in Ontario, central Canada. Trichothecene genotypes of F. graminearum isolated from corn (n = 452) and wheat (n = 110) from 2010 to 2012 were identified. All the isolates were deoxynivalenol (DON) type. About 96% of corn isolates and 98% of wheat isolates were 15‐acetyl deoxynivalenol (15ADON) type. The fungal population structures from corn (n = 313) and wheat (n = 73) were compared using 10 variable number tandem repeat (VNTR) markers. The fungal populations and subpopulations categorized based on host, cultivar groups, years and geography showed high gene (H = 0.818–0.928) and genotypic (GD = 0.999–1.00) diversity. Gene flow was also high between corn and wheat population pairs (Nm = 8.212), and subpopulation pairs within corn (Nm = 7.13–23.614) or wheat (Nm = 19.483) populations. Phylogenetic analysis revealed that isolates from both hosts were F. graminearum clade 7. These findings provide baseline data on 3‐acetyl deoxynivalenol (3ADON) and 15ADON profiles of F. graminearum isolates from corn in Canada and are useful in evaluating mycotoxin contamination risks in corn and wheat grains. Understanding the fungal genetic structure will assist evaluation and development of resistant cultivars/germplasm for FHB on wheat and GER on corn.     

Colonization of soft wheat following infection of the stem base by Fusarium culmorum and translocation of deoxynivalenol to the head

Following inoculation of the base of soft wheat seedlings with Fusarium culmorum, disease symptoms typical of crown rot developed at the stem base and extended up to the third node by plant maturity. Fungus was isolated from all tissues exhibiting symptoms but not from symptomless tissues. Histopathological analysis revealed that the fungus was present mainly in the parenchymatic cells of the stem base and colonized the tissues via apoplastic and symplastic pathways. Host response in advance of pathogen colonization was observed. At maturity, plants were divided into sections from the inoculated area to the head. Heads were also separated into grain, rachis and chaff components. Colonization by the fungus was assessed by isolation from surface‐sterilized segments and quantified by real‐time PCR. Disease symptoms and the fungus were detected up to the third node, while deoxynivalenol (DON) was present in all stem segments and heads. Within the head, the DON concentration was higher in the rachis than in the chaff and grain components. These results demonstrate that F. culmorum can extensively colonize stem tissues but not reach the head by the time of plant maturity. In contrast, DON was detected in tissues beyond those colonized by the fungus, translocating to the head where, although accumulating mainly in the rachis, significant quantities accumulated in the grain. These findings indicate that there is a potential threat of contamination of grain with DON where severe crown rot is present in a crop.     

Effect of temperature and duration of wetness during initial infection periods on disease development, fungal biomass and mycotoxin concentrations on wheat inoculated with single, or combinations of, Fusarium species

Experiments were conducted under controlled environment conditions to study the relationship between environmental conditions, development of fusarium head blight (FHB) and mycotoxin production. A single isolate from each of four Fusarium species ( F. avenaceum , F. culmorum , F. graminearum and F. poae ) was used to inoculate wheat ears separately. Combinations of two or three isolates were also used to inoculate ears simultaneously. Inoculated ears were subjected to various combinations of duration of wetness (6–48 h) and temperature (10–30°C). For all inoculations, both incidence of spikelets with FHB symptoms and concentration of mycotoxins generally increased with increasing length of wetness period and temperature. There were significant positive correlations among disease incidence, fungal biomass (quantified as total amount of fungal DNA) and mycotoxins. Mycotoxin production was also greatly enhanced by high temperatures (≥ 20°C) during initial infection periods. In single-isolate inoculations, F. poae was the least aggressive. There was no evidence to support synergetic interactions between fungal isolates in causing visual symptoms; rather the results suggest, in most cases, the presence of competitive interactions. Furthermore, the competition led to large reductions in fungal biomass compared to single-isolate inoculations, often > 90% reduction for the weaker isolate(s). In contrast, mycotoxin productivity increased dramatically in the co-inoculations, by as much as 1000 times, suggesting that competition resulted in greater production of trichothecene mycotoxins. The F. graminearum isolate was most competitive and isolates of the other three species were similar in their competitiveness.     

Early PCR-based detection of Fusarium culmorum,F. graminearum,F. sporotrichioides and F. poae on stem bases of winter wheat throughout Poland

Foot rot and crown rot are fungal diseases of wheat caused by a complex of Fusarium species. They have a huge economic impact mainly due to yield reduction. A survey was conducted to identify four Fusarium species, occurring on wheat stem bases, using species-specific PCR assays in samples collected during spring of 2012. The dominant species was F. graminearum, which was identified in above 64 % of samples. F. culmorum was detected in 15.71 %, F. poae in 15.71 % and F. sporotrichioides in 5.71 % wheat fields. Most of the wheat fields in the eastern Poland were infected with at least one or two of Fusarium species, while in central Poland no Fusarium species were identified in most of the fields. The presence of F. graminearum tends to favor the presence of F. culmorum and this effect was visible also for F. poae and F. sporotrichioides. The frequency of F. graminearum and F. culmorum detections were highest where wheat crops were preceded by maize and in the samples from late sown fields. The opposite observation was made for F. poae and F. sporotrichioides, where the number of detections of these species was higher in samples from early sown fields. The number of detected Fusarium species was significantly lower in samples collected from fields protected with autumn herbicide in comparison to unprotected fields. The rate of autumn N fertilization did not affect the number of Fusarium detections.     

Trichothecene mycotoxin genotypes of Fusarium graminearum sensu stricto and Fusarium meridionale in wheat from southern Brazil

A total of 82 fungal isolates was obtained from wheat kernel samples affected by fusarium head blight collected from 20 locations in southern Brazil. Polymerase chain reaction (PCR) assays were used to characterize trichothecene mycotoxin genotypes [deoxynivalenol (DON), nivalenol (NIV) and two acetylated derivatives of DON]. To identify isolates that producing DON and NIV, portions of the Tri13 gene were amplified. To identify 3-acetyl-deoxynivalenol (3-ADON) and 15-acetyl-deoxynivalenol (15-ADON) genotypes, portions of Tri3 and Tri12 were amplified. Nearly all of the isolates studied (76/82) were of the DON/15-ADON genotype. Six of the isolates were of the NIV genotype. The DON/3-ADON genotype was not observed. Portions of three genes were sequenced from representative isolates of the NIV and DON/15-ADON genotypes and compared with sequences from curated reference isolates of Fusarium in GenBank. blast queries for individual gene sequences and pairwise comparisons of percentage identity and percentage divergence based on 1676 bp of concatenated DNA sequence suggested that the isolates representing the DON/15-ADON genotype were Fusarium graminearum sensu stricto and the isolates representing the NIV genotype were Fusarium meridionale . This is the first detailed report of trichothecene mycotoxin genotypes of F. graminearum and F. meridionale in Brazil.     

Mycelial compatibility reactions of Australian Fusarium graminearum and F. pseudograminearum isolates compared with AFLP groupings

Using the mycelial reactions of 435 combinations of 14 Fusarium pseudograminearum and 15 F. graminearum isolates, it was demonstrated for the first time that mycelial reactions/barrage formation cannot be clearly used to distinguish F. graminearum and F. pseudograminearum. Mutually compatible isolates produced very different patterns of compatibility with other isolates. However, about 60% of pairings between F. graminearum and F. pseudograminearum isolates were compatible, indicating common ancestry. The Mantel tests used to determine any possible associations between mycelial compatibility reactions and AFLP genotypic diversity data revealed no association between the two systems in either species. In addition, no association was found between mycelial compatibility reactions and sexual reproduction in the two species. Implications of the higher frequency of mycelial compatibility reactions observed in F. pseudograminearum than in F. graminearum are discussed.     

Effect of temperature on head blight of wheat caused by Fusarium culmorum and F. graminearum

The effect of small temperature differentials (16 vs. 20°C) on the pathogenicity of deoxynivalenol producing single isolates of Fusarium culmorum and F. graminearum and on the fusarium head blight (FHB) response of eight wheat cultivars was examined. Fusarium culmorum inoculation caused greater visual disease symptoms at 20°C than at 16°C, both overall and on an individual cultivar basis (overall AUDPC = 13·5 and 9·6, respectively) ( P  < 0·05). In contrast, F. graminearum inoculation caused greater overall visual disease symptoms at 16°C than at 20°C, both overall and at the individual cultivar level (overall AUDPC = 12·8 and 10·9, respectively) ( P  < 0·05). Results showed both F. culmorum and F. graminearum inoculations caused a greater loss in yield at 20°C (54·3 and 46·9% relative 1000-grain weight, respectively) compared with 16°C (73·3 and 66·9% relative 1000-grain weight, respectively) ( P  < 0·05). Fusarium culmorum -inoculated heads contained similar amounts of fungal DNA at both 16 and 20°C (1·9 and 1·7 ng mg⁻¹ of plant material, respectively) (not significant), while for F. graminearum inoculation, plants contained higher amounts of fungal DNA at 20°C (2·0 and 1·0 ng mg⁻¹ of plant material, respectively) ( P  < 0·05). Overall, there was a significant negative correlation between AUDPC and percentage relative 1000-grain weight at both 16 and 20°C ( r  =−0·693 and −0·794, respectively, P  < 0·01).     

Geographic distribution and genetic diversity of Fusarium graminearum and F. asiaticum on wheat spikes throughout China

A large number of Fusarium graminearum and F. asiaticum isolates were collected from wheat spikes from all regions in China with a history of fusarium head blight (FHB) epidemics. Isolates were analysed to investigate their genetic diversity and geographic distribution. Sequence characterized amplified region (SCAR) analyses of 437 isolates resolved both species, with 21% being F. graminearum (SCAR type 1) and 79% being F. asiaticum (SCAR type 5). AFLP profiles clearly resolved two groups, A and B, that were completely congruent with both species. However, more diversity was detected by AFLP, revealing several subgroups within each group. In many cases, even for isolates from the same district, AFLP haplotypes differed markedly. Phylogenetic analyses of multilocus DNA sequence data indicated that all isolates of SCAR type 1, AFLP group A were F. graminearum , whilst isolates of SCAR type 5, AFLP group B were F. asiaticum , demonstrating that it is an efficient method for differentiating these two species. Both species seem to have different geographic distributions within China. Fusarium graminearum was mainly obtained from wheat growing in the cooler regions where the annual average temperature was 15°C or lower. In contrast, the vast majority of F. asiaticum isolates were collected from wheat growing in the warmer regions where the annual average temperature is above 15°C and where FHB epidemics occur most frequently. This is the first report of the distribution of, and genetic diversity within, F. graminearum and F. asiaticum on wheat spikes throughout China.     

Control of Microdochium majus in winter wheat with botanicals – from laboratory to the field

The fungal pathogen Microdochium majus, causing snow mould, seedling blight and foot rot, results in severe yield losses in small grain cereals. There are few options to control this pathogen in organic production. In this study, aqueous extracts or botanical powders prepared from chamomile, meadowsweet, thyme and Chinese galls were tested in vitro against M. majus conidia germination and mycelial growth, respectively. Subsequently, three botanicals were chosen, applied as powders with different seed coating adhesives, and tested for their effect on the incidence of M. majus from naturally infected wheat seed lots and on seedling emergence from soil under controlled environmental conditions. Furthermore, seed treatments with warm water, a bacterial product or one chosen botanical were tested in a growth chamber and in a field experiment over three consecutive years. Of the botanicals tested, Chinese galls showed the highest efficacy in controlling M. majus, reducing conidia germination and mycelial growth by up to 97 and 100%, respectively, and reducing the incidence from infested seeds by up to 59%. In two growth chamber experiments, total seedling emergence increased by up to 30 and 59% compared with the control treatments following an application with Chinese galls. Under field conditions, yield increase through Chinese galls, the bacterial product and the warm water treatment was 19, 10 and 37% compared with the untreated control, respectively. This study demonstrates the potential of Chinese galls to control M. majus in wheat. Options for improved formulations or combinations of heat‐based treatments with Chinese galls are discussed.     

Aetiology and toxigenicity of Fusarium graminearum and F. pseudograminearum causing crown rot and head blight in Australia under natural and artificial infection

Globally fusarium head blight (FHB) of wheat is predominantly caused by Fusarium graminearum (FG) and crown rot (FCR) by F. pseudograminearum (FP). While both FG and FP can cause FHB in Australia, the reasons why the morphologically and culturally similar FG is not a major FCR pathogen has remained elusive. Using aetiology and toxigenicity, this study clarifies the contrasting roles of FG and FP in FCR and FHB in Australia. Naturally infected wheat from 42 sites during 2010 FHB epidemics, and wheat inoculated with either pathogen to induce FCR or FHB at three field plantings in 2011, were used to determine pathogen prevalence and deoxynivalenol (DON) content of the crown, stem base, stem top, rachis and grain. As the primary aetiological agent, FP prevalence in the crown correlated with FCR severity while FG in grain and/or the rachis correlated with FHB severity. FG was an effective colonizer of the crown and stem base but colonization was symptomless. DON content was linked to FG biomass in all tissues except the crown, where FP biomass was the main contributor. Of the 30 measures derived to analyse pathogen fitness in 2011, 10 described the superior fitness of FG for FHB; six defined FP fitness for FHB including inoculum dispersal; and eight defined FCR fitness of both FP and FG. FG had superior FHB fitness but weak saprophytic survival may have undermined its FCR fitness.     

Role of Deoxynivalenol in Aggressiveness of Fusarium graminearum and F. culmorum and in Resistance to Fusarium Head Blight

The data available indicate that aggressiveness of Fusarium graminearum and F. culmorum depends on their deoxynivalenol (DON) and nivalenol-producing capacity: toxin-producing ability correlated closely with the level of aggressiveness measured. This agrees well with other literature findings. However, the resistance of a cultivar influenced DON production significantly. In the most resistant genotypes, toxin contamination remained near zero, whereas the same isolates and inoculum produced very high toxin levels in susceptible cultivars. As toxin levels were correlated with the ratio of Fusarium-damaged kernels (FDK) and this ratio is very low in highly resistant cultivars, the conclusion is that the level of resistance level is more important in governing DON accumulation in a given cultivar than is the aggressiveness of an isolate. In susceptible cultivars, DON producing ability is decisive, but in highly resistant cultivars resistance is the major factor in suppressing disease development and DON accumulation. In different years, the same FDK values were associated with different DON concentrations and this depended very much on the precipitation towards the end of May, the time of inoculation.     

Evaluation and characterization of resistance to fusarium head blight caused by Fusarium culmorum in UK winter wheat cultivars

Fusarium head blight (FHB) resistance of 50 cultivars from the National List of winter wheat cultivars approved for sale (or were undergoing trails for approval in 2003) in the UK was compared with 21 reference cultivars from continental Europe which had previously been characterized for resistance. Only three UK National List cultivars (Soissons, Spark and Vector) had stable resistance over trial sites that was significantly greater than that of the FHB susceptible cultivar Wizard. In addition, under moderate disease pressure, 21 of the National List cultivars had levels of the trichothecene mycotoxin deoxynivalenol (DON) above the proposed European Union limit of 1·25 ppm in grain. Surveys show that levels of FHB and DON in the UK crop are currently very low, however, should disease pressure increase for any reason, then an improvement in the overall levels of FHB resistance of UK winter wheat germplasm will be required. In order to infer the origin of resistance and to identify potentially novel resistance, allele sizes of microsatellite (simple sequence repeat, SSR) markers linked to quantitative trait loci (QTL) for FHB resistance were compared between the test cultivars and known, characterized resistance sources. The major FHB resistance QTL from the Chinese cv. Sumai-3 (3BS, 5A and 6B), the Romanian cv. Fundulea F201R (1B and 5A) and the French cv. Renan (5AL) were screened with 17 SSRs. No National List cultivar had haplotypes similar to any of these QTL. However, the highly resistant German reference cultivar Petrus had an identical haplotype to cv. Fundulea F201R on 1B indicating that this cultivar has an allelic FHB resistance QTL at that location.     

Head infection and accumulation of Fusarium toxins in kernels of 12 barley genotypes inoculated with Fusarium graminearum isolates of two chemotypes

Twelve barley genotypes were inoculated with two F. graminearum isolates of different chemotype I₁ #148 (producing nivalenol/deoxynivalenol) and I₂ #108 (deoxynivalenol/acetyldeoxynivalenol). For both I₁ and I₂ isolates, respectively, reductions (%) in number of kernels head^-1 10.6 and 14.3; yield 39.6 and 35.7; weight of 1000 kernels 36.9 and 23.2 were observed in inoculated plants from control values. Chemical analysis revealed the presence (average concentration mg kg^-1) of deoxynivalenol (1.3) and nivalenol (3.2) in kernels of all genotypes inoculated with the I₁ isolate, and zearalenone (0.2) in three samples. After inoculation with the I₂ isolate, deoxynivalenol (37.8) and zearalenone (0.4) were found in kernels of all genotypes, while 3-acetyldeoxynivalenol and 15-acetyldeoxynivalenol, respectively, were determined in five and four samples only. No significant correlation between examined characteristics was found for either the I₁ or I₂ isolate. The results obtained contribute information on the accumulation of toxins in cereal grain inoculated with F. graminearum isolates of different chemotypes.     

Visual disease and PCR assessment of stem base diseases in winter wheat

Stem base disease (eyespot, sharp eyespot and brown foot rot) was assessed visually and by the polymerase chain reaction (PCR) technique on single plants sampled at four-week intervals in two crops of winter wheat grown in the UK in 1992–3. PCR assays were conducted for Fusarium avenaceum , F. culmorum , both varieties of Microdochium nivale , both eyespot-causing species of Tapesia and Rhizoctonia cerealis . PCR diagnoses were compared with visual diagnoses at each time point. Eyespot was caused principally by T. acuformis (R-type) and developed rapidly late in the season. Visual diagnoses of eyespot were largely confirmed by PCR but T. acuformis was detected in many plants lacking eyespot symptoms. R. cerealis was detected at relatively low incidences on both sites, and sharp eyespot visual diagnoses did not correlate with the incidence of any of the pathogens assayed by PCR. Brown foot rot, caused principally by Microdochium nivale var . majus , accumulated earlier in the season than eyespot. Overall, visual diagnoses of stem base disease coincided poorly with PCR data until after growth stage (GS) 30.     

Comparison of visual head blight ratings, seed infection levels, and deoxynivalenol production for assessment of resistance in cereals inoculated with Fusarium culmorum

Seven spring wheat, 13 barley, 14 oats and 20 winter wheat genotypes were inoculated at flowering in 1993 and 1994 with mixed conidial suspensions of 8 isolates of Fusarium culmorum. Four weeks after inoculation, head blight was recorded in the field. After harvest, seed infection was assessed by a Freezing Blotter Test in the laboratory. Seed samples were also analyzed for deoxynivalenol (DON) content. Differences were found in head blight rating, the levels of infected seeds and the DON content between wheat, barley, and oats and between cultivars. Highly significant correlations were found between the percentage of heavily infected seed and the DON content. The weighted mean value of infected seeds and DON content were also significantly correlated. No significant correlation was found between head blight rating in the field and DON content. The level of infected seeds, as determined by the Freezing Blotter Test, was a better indication of the DON content in the seeds than the head blight rating. This visual assessment of levels of infected seeds gives a reliable estimate of resistance to Fusarium.     

Induction of systemic disease resistance and pathogen defence responses in Asparagus officinalis inoculated with nonpathogenic strains of Fusarium oxysporum

The ability of nonpathogenic isolates of Fusarium oxysporum (np Fo ) to induce systemic resistance and defence responses against subsequent challenge with a pathogenic strain of F. oxysporum f. sp. asparagi ( Foa ) was examined in Asparagus officinalis . In a split-root experiment, roots inoculated with np Fo exhibited a hypersensitive response and those subsequently inoculated with Foa displayed resistance. Induction of systemic resistance in np Fo -treated plants led to significantly fewer necrotic lesions ( P  = 0·05) and reduced Foa disease severity compared with plants not treated with np Fo . In hyphal-sandwich root inoculation experiments, activities of peroxidase and phenylalanine ammonia-lyase and lignin content were higher in np Fo -treated plants and increased more rapidly than in np Fo -untreated plants after Foa inoculation. Antifungal activity (inhibition of fungal spore germination and germ-tube growth) from exudates of roots inoculated with Foa were observed for np Fo -treated plants but not for np Fo -untreated plants. Thus, isolates of np Fo may function as inducers of systemic acquired resistance (SAR) and defence responses against Foa invasion in A. officinalis .