**6. FGSC fitness vary**

Phylogenetic analyses of trichothecene gene cluster demonstrated that genotype polymorphism is trans-specific and have been maintained by balancing selection on the ancestral pathogens, and genotype differences may have a significant impact on pathogen fitness [29].

The FGSC strains with different genotype showed different fitness to the ecological environment, such as the hosts, temperature, rotation, and so on. 3-ADON producer was more aggressive than 15-ADON population in susceptible wheat, and also the 3-ADON isolates exhibit a higher DON production than the 15-ADON isolates. Similar conclusions were made by Zhang et al. [28] that *F. asiaticum* strains with 3-ADON chemotype revealed significant advantages over the strains that produce NIV in pathogenicity, growth rate, trichothecene accumulation, etc. Their data also indicated that the growth of rice may be a key factor for the presence of *F. asiaticum* [28]. Liu et al. [30] compared the fitness of three chemotype *Fusarium* strains, and found that 15ADON producers had the advantage in perithecia formation and ascospore release, whereas more DON were produced by the 3-ADON chemotypes. Qiu and Shi [22] estimated the effect of rice or maize as former crops on mycotoxin accumulation in wheat grains, and they concluded that rice-wheat rotation favors DON accumulation.

Changes in DON chemotypes distribution were reported for FGSC from Canada, USA, and Northern Europe. Recently, Nicolli et al. [31] assessed a range of fitness-related traits (perithecia formation, mycelial growth, sporulation and germination, pathogenicity, and sensitivity to tebuconazole) with 30 strains representatives of 3ADON-, 15ADON-, and NIV-producers. The pathogenicity assay results indicated that strains with the DON chemotypes were generally more aggressive than the NIV ones [31].

Phenotypic analyses indicated that *F. asiaticum* with a 3-ADON genotype revealed significant advantages over *F. asiaticum* that produce NIV in pathogenicity, growth rate, and trichothecene mycotoxin accumulation. It shall be noted that a biased gene flow from 3-ADON to NIV producers was identified in *F. asiaticum* from wheat in China [28].

**71**

Fusarium graminearum *Species Complex and Trichothecene Genotype*

differences were found in the frequencies of *F. graminearum sensu stricto* and *F. asiaticum* species within the hosts with *F. graminearum sensu stricto* to be the dominant. Genotype analysis revealed that 15-ADON producers represented 92.7 and 98.5% of isolates from wheat and maize, respectively. The three genotypes may affect species distribution or population ecology because these mycotoxins are differing in toxic-

Traditionally, chemotyping of FGSC strains has been carried out using gas chromatography/mass spectroscopy. This method can be time-consuming and expensive. The genome sequences of several FGSC strains have been published. The trichothecene core gene cluster nucleotide sequences of many strains representatives 3-ADON, 15-ADON, and NIV genotypes have also been deposited in the GenBank. The availability of this information makes it possible to reveal the structural features and allowed selection of several primer sets used successfully in PCR experiments for the molecular characterization of the various chemotypes. Molecular genetic assays

Lee et al. [34] sequenced the gene cluster for trichothecene biosynthesis from a 15-ADON producer (strain H-11) and a NIV producer (strain 88-1), and sequence polymorphisms within the *Tri7* open reading frame was found between the two strains. Alignment analysis suggesting that the *Tri7* gene of H-11 carried several mutations and an insertion compared to the *Tri7* gene from 88-1, and based on the sequence difference a PCR-based diagnostic method for differentiating DON and

Lee et al. [35] subsequently sequenced the *Tri13* homolog from DON (strain H-11) and NIV producers (strain 88-1) and found that the gene differs drastically between the two producers, suggesting that the *Tri13* gene could be used for genetic genotype distinction for DON and NIV producers [35, 36]. They further confirmed the roles of the *Tri7* and *Tri13* genes in trichothecene production, and the results suggested that both the *Tri7* and *Tri13* genes are nonfunctional in DON producers [35]. The PCR assays to *Tri7* and *Tri13* genes developed by Lee et al. [34, 35] allowed clear differentiation between DON and NIV genotypes. However, they could not be used to further classify the DON-producing isolates to 3-ADON or 15-ADON producer. Ward et al. [29] examined a 19-kb region of the trichothecene gene cluster that sequenced in 39 strains representing 3-ADON, 15-ADON, and NIV genotypes. They found that Tri-cluster haplotypes group according to genotype rather than by species indicated that 3-ADON, 15-ADON, and NIV genotypes each have a single evolutionary origin. Reciprocally monophyletic groups, corresponding to each of 3-ADON, 15-ADON, and NIV genotypes, were strongly supported in *Tri3*, *Tri11*, and *Tri12* genes trees. Two sets of primers specific to the individual genotypes were designed from *Tri3* and *Tri12* genes. The genotype-specific PCR tests developed by Ward et al. [29] provide a rapid and direct genetic method for distinguishing among 3-ADON, 15-ADON, and NIV producer, this is the first report differentiated

The work by Lee et al. [34, 35] and Brown et al. [37] indicated that the genes *Tri13* and *Tri7* from trichothecene biosynthetic cluster are responsible for conversion of DON to NIV (*Tri13* gene) and the *Tri7* gene product modifies NIV by acetylation of C-4 atom hydroxyl to produce 4-ANIV. Based on these results sets of positive-negative PCR assays to *Tri7* and *Tri13* genes for trichothecene determination of FGSC were developed by Chandler et al. [38], and the assays can accurately indicate a DON or NIV genotype in FGSC, *F. culmorum* and *F. cerealis*. The assays

allow for high throughput screening of large numbers of field isolates.

NIV producers by polyacrylamide gel electrophoresis was developed.

these three genotype strains by a PCR method.

*DOI: http://dx.doi.org/10.5772/intechopen.89045*

**7. Genetic genotype determination of FGSC**

ity and bioactivity [7, 29, 33].

FGSC from wheat-maize rotation regions on wheat spikes and maize stalks in Henan province, China, was determined by Hao et al. [32], and significant

*Mycotoxins and Food Safety*

were proposed.

**6. FGSC fitness vary**

pathogen fitness [29].

rotation favors DON accumulation.

than the NIV ones [31].

from wheat in China [28].

FGSC members are climate dependent [20].

tively, which is consistent with earlier studies [20, 26, 27].

*sensu stricto* and *F. asiaticum* on wheat spikes in China. A comprehensive study on FGSC from wheat was conducted by Zhang et al. [20]. They found that the geographic distribution of FGSC associated with the annual average temperature. The

*F. graminearum sensu stricto*, while the warmer regions (annual average temperature ≥15°C) appear to favor *F. asiaticum*. A hypothesis was made that the distribution of

*F. graminearum sensu stricto* with the 15-ADON genotype and *F. asiaticum* with either the NIV or the 3-ADON genotype were the dominant causal agents on wheat, and the two species dominated the northern and southern regions of China, respec-

However, more recently the study by Zhang et al. [28] indicated that temperature may not be the only factor in the distribution of FGSC and that other, yet unknown factors affected their distribution. To explain genotype distribution in different geographic areas, hypotheses based on grain seed shipment, international trade, long-distance spore transportation, and environmental favorable conditions

Phylogenetic analyses of trichothecene gene cluster demonstrated that genotype polymorphism is trans-specific and have been maintained by balancing selection on the ancestral pathogens, and genotype differences may have a significant impact on

The FGSC strains with different genotype showed different fitness to the ecological environment, such as the hosts, temperature, rotation, and so on. 3-ADON producer was more aggressive than 15-ADON population in susceptible wheat, and also the 3-ADON isolates exhibit a higher DON production than the 15-ADON isolates. Similar conclusions were made by Zhang et al. [28] that *F. asiaticum* strains with 3-ADON chemotype revealed significant advantages over the strains that produce NIV in pathogenicity, growth rate, trichothecene accumulation, etc. Their data also indicated that the growth of rice may be a key factor for the presence of *F. asiaticum* [28]. Liu et al. [30] compared the fitness of three chemotype *Fusarium* strains, and found that 15ADON producers had the advantage in perithecia formation and ascospore release, whereas more DON were produced by the 3-ADON chemotypes. Qiu and Shi [22] estimated the effect of rice or maize as former crops on mycotoxin accumulation in wheat grains, and they concluded that rice-wheat

Changes in DON chemotypes distribution were reported for FGSC from Canada, USA, and Northern Europe. Recently, Nicolli et al. [31] assessed a range of fitness-related traits (perithecia formation, mycelial growth, sporulation and germination, pathogenicity, and sensitivity to tebuconazole) with 30 strains representatives of 3ADON-, 15ADON-, and NIV-producers. The pathogenicity assay results indicated that strains with the DON chemotypes were generally more aggressive

Phenotypic analyses indicated that *F. asiaticum* with a 3-ADON genotype revealed significant advantages over *F. asiaticum* that produce NIV in pathogenicity, growth rate, and trichothecene mycotoxin accumulation. It shall be noted that a biased gene flow from 3-ADON to NIV producers was identified in *F. asiaticum*

FGSC from wheat-maize rotation regions on wheat spikes and maize stalks in Henan province, China, was determined by Hao et al. [32], and significant

cooler temperatures (annual average temperature ≤15°C) appear to favor

**70**

differences were found in the frequencies of *F. graminearum sensu stricto* and *F. asiaticum* species within the hosts with *F. graminearum sensu stricto* to be the dominant. Genotype analysis revealed that 15-ADON producers represented 92.7 and 98.5% of isolates from wheat and maize, respectively. The three genotypes may affect species distribution or population ecology because these mycotoxins are differing in toxicity and bioactivity [7, 29, 33].
