**4.2. Terpenoids**

(cell wall-bound) forms [31]. The major portion of phenolic compounds is in the outer part of grains. Moreover, phenolic acids, predominantly ferulic and coumaric acid, play an important role in limiting polysaccharide degradation by exogenous enzymes, where they act as a

Phenolic compounds in plants are involved in the interaction between the pathogen and the plant. For example, the phenolic acids accumulated throughout the development of wheatkernel development impact positively the resistance to *Fusarium* [33]. It has been reported the fungicidal efficiency of phenolic compound considering IC50 values. These values rank

It has been stated that the most maize-resistant genotypes exhibited high levels of phenylpropanoids, which were related to low levels of disease severity and grain fumonisin (FUMO) concentration [34]. In a study using wheat cultivars (winter and spring), significantly higher amounts of free phenolic compounds were found in the glumes, lemmas and paleas of the spring cultivar prior to and at all sampling times after inoculation, in comparison to the winter wheat cultivar. The spring cultivar exhibited resistance against initial infection by the fungus. It was found that the amount of *p*-coumaric acid increased significantly in the glumes,

cross-link between polysaccharides and between polysaccharides and lignin [32].

28 Fusarium - Plant Diseases, Pathogen Diversity, Genetic Diversity, Resistance and Molecular Markers

between 0.7 and >10 mM [30].

**Figure 2.** Cereal secondary metabolites with antifungal activity.

Terpenes are the most numerous and structurally diverse plant natural products. The plethora of terpenoid compounds is biosynthetically assembled from only two simple precursors, isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). Plant terpenoids include compounds ranging from C5 hemisesquiterpenes to C40 tetraterpenes, with diverse physical and chemical properties leading to lipophilic or hydrophilic, volatile or non-volatile metabolites [44].

Several terpenoids have their roles in plant defense against biotic and abiotic stresses, or they are treated as signal molecules to attract the insects of pollination. In a study using cyclic terpenes (limonene, menthol, menthone and thymol) against *F. verticillioides*, limonene and thymol showed the highest inhibitory effects on *F. verticillioides* development. Thymol was the most active inhibitor of fumonisin B1 biosynthesis [45].

In the last year, essential oils, which composition mainly include terpenes and terpenoids, from different plants were used in the prevention of fungi and mycotoxins accumulation in cereals. A study using *Melissa officinalis*, *Salvia officinalis*, *Coriandrum sativum*, *Thymus vulgaris*, *Mentha piperita* and *Cinnamomum zeylanicum* showed that all these essential oils have an inhibitory effect on fungal contamination of wheat seeds. This ability was dose-dependent. Regarding mycotoxin development, the best control on fumonisins production was recorded for *Cinnamomum zeylanicum* [46]. Similar findings regarding essential oils were done by Daferera et al. [47]; *Fusarium* sp. was completely inhibited by oregano, thyme, dictamnus and marjoram essential oils at moderately low concentrations (85–300 μg/mL). Also, oils from *Cymbopogon citratus*, *Ocimum basilicum* and *Ocimum gratissimum* were the most effective *in vitro*, completely inhibiting the growth of *F. verticillioides*. The application of these oils at concentrations of 8, 6.4 and 4.8 μL/g inhibit the growth of *F. verticillioides* in maize for a period of 21 days. It was also observed that the production of fumonisin was not affected by the lower concentration (4.8 μL/g) [48].

On the other hand, in a cromatografy study, volatile organic compounds (VOCs) were identified using GC-MS in oats, barley and wheat infected by three species of *Fusarium*, including species that caused cortical rot disease in wheat, and two terpenes were identified (linalool and β-caryophyllene), which found higher concentrations with respect to the controls [49].

been attached to them [55]. Benzoxazinoids are synthesized in the shikimate pathway from the amino acid tryptophan. They are present in maize; wheat, rye and certain wild barley species, however, have not been found in cultivated barley varieties, oat or rice. Bxs are stored in an inactive glucoside form in plant vacuoles or plastids to avoid toxicity to the plant itself; through the enzymatic activation and chemical degradation, the tissue disrupted form the active benzoxazinoid [56]. In a research using wheat, principal component analyses demonstrated a correlation between the susceptibility to FHB and the concentrations of range of Bxs [57]. The benzoxazinoid 2-β-glucopyranoside-2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3 one (DIMBOA-glc), α-tocopherol and the flavonoids homo-orientin and orientin were identified as potential inhibitors of (deoxynivalenol) DON accumulation in a study with wheat that

*Fusarium* Mycotoxins and Metabolites that Modulate Their Production

http://dx.doi.org/10.5772/intechopen.72874

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correlates accumulation in *Fusarium*-infected winter and spring wheat cultivars [58].

**5. Possible mechanisms and management that modulate inhibition** 

risk of *Fusarium* infection, for avoid that flowering coincides with spore release.

address other types of strategies.

Alternatives to chemical fungicides, such as biocontrol agents, have been tested extensively in both the greenhouse and field environment, but the toxins of *Fusarium* control efficacy under field conditions have not been consistent [62]. However, some of the strategies to reduce contamination at the crop level are not always effective, so at the storage level it is sought to

**of mycotoxin production of** *Fusarium* **species**

of detoxification.

A plethora of secondary metabolites have been reported to inhibit *Fusarium* and their mycotoxins; however, the molecular mechanisms of plant resistance to both are needed to provide a deeper understanding of the mode of actions of the metabolites as well as the mechanisms

Mycotoxins produced by *Fusarium* spp. include different compounds with trichothecenes, fumonisins, zearalenone and emerging toxins such as fusaproliferin, enniatins, beauvericin and moniliformin [10]. This mycotoxins genus can infect cereals directly during ripening, harvesting or storage, the crop soil affecting plant growth and development, which makes its eradication complex and difficult, but various strategies are used to reduce this contamination, butte the best strategies cannot completely eradicate mycotoxin contamination. Prevention strategies during cultivation and storage aim to eliminate mycotoxins; some of the strategies used are crop rotation; in this sense, Schaafsma et al. [59] observed in a 4-year study that planting a crop other than wheat 2 years previous to planting a wheat crop significantly decreased the level of DON in wheat grain in 1 year out of four. This type of studies support the theory that crop residues are the source of *Fusarium* toxin inoculum, so alternating crops would reduce the possibility of contamination. However, studies such as that reported by Fernández-Blanco et al. [25] indicate that wheat grown consecutively (each year) has less contamination by *Fusarium* toxins than alternately grown wheat. Urea fertilization is another strategy to reduce contamination by *Fusarium* sp. as mentioned by Teich [60] and Martin et al. [61], where they applied urea instead of ammonium nitrate, with fewer pollution symptoms observed. Among the aspects to consider in order reducing *Fusarium* contamination is the cultivation season, since it has been documented that winter varieties develop and mature before spring varieties, which reduce the

The metabolomics as a tool helped in to identify the metabolites in barley that are related to resistance against *Fusarium* head blight FHB exposed that metabolites conferring resistance mainly belonged to phenylpropanoid, flavonoid, fatty acid and terpenoid metabolic pathways [50]. A research by Wang et al. [51] exposed a number of genes involved in secondary metabolites biosynthesis are specifically responsive to *F. verticillioides* inoculation in BT-1 kernels. Terpenoid biosynthesis and diterpenoid biosynthesis were particularly increased by *F. verticillioides* inoculation. See Ref. [29] to review a list of terpenoids conferring resistance to *Fusarium*.
