**3. Source of inoculum and infection pathway**

Many *Fusarium* spp. have been reported to cause the various diseases in maize but the most devastating fungal agent for ear rot and stalk rot diseases is *F*. *verticillioides* [32, 33]. Ear rot and stalk rot diseases are two most important *Fusarium* disease of maize occurs worldwide. The significance of these diseases has been witnessed by the world for many decades. Maize plant residues present in nearby fields is the primary and important source of inoculums for infections of maize plant [34]. Many *Fusarium* spp. successfully survive on maize crop residue or in the soil as mycelium or other structures like *F. graminearum* produces chlamydospores and *F. verticillioides* (reported as *F. moniliforme*) can produce thickened hyphae capable of colonizing senescent tissues of the host plant [24, 35]. *F. verticillioides*, *F. subglutinans* and *F. proliferatum* produce large numbers of microconidia and macroconidia on crop residues, and may act as the most important inoculum for *Fusarium* ear rot and symptomless kernel infection [25]. Though *Fusarium* spp. are commonly seed borne but the role of seed as an inoculum source for further infection has always been a matter of controversy [36]. According to Cotten and Munkvold, the surface residues may be the potential reservoir of recolonization and spore production for airborne inoculums contributing significantly in spreading of the disease into the next vegetation period [16]. *Fusarium* spp. can enter the host plant through different pathways and starts primarily from root infection, through stalk nodes or through injuries in the stalk made by various biotic agents, silk infection and systematic spread after root penetration [24, 37, 38]. In stalk rot disease, the *Fusarium* spp. enter the stalk systematically after the successful colonization of root through various ways such as seed transmission, young leaf sheath and via wounds created by hail or insects [33, 39]. At maturity, both root and lower stalk lose their metabolic activities weakening the plant defense system against infection [40]. The other factors such as drought, high plant density, leaf diseases, and corn borer attacks decreases photosynthesis rate in the host plant and may contribute in stalk rot disease development [40]. The major infection pathways taken up by most *Fusarium* spp. for maize ears infection is via silk which occurs severely at early stage of silk development [41]*.* There are three major entry points for ear infection: (1) landing and germination of fungal spores on the silk and moving down the silk to infect the kernels and rachis; (2) through injuries made by biotic agents and hail; (3) through systematic infection of *F*. v*erticillioides* [24]. The important factors which appears to be affecting the range of different species of both ear and stalk rot infection are temperature and moisture [42]. However, the timing and significance of infection pathways may vary from one geographical region to another depending upon the weather conditions and occurrence of biotic agents. *F*. *graminearum* and *F*. *culmorum* are reported to cause the ear rot infection at low temperatures and high precipitation whereas *F*. *verticillioides*, *F*. *subglutinans* and *F*. *proliferatum* are responsible at high temperatures and dry conditions [25, 43].

### **4. Fusarium associated mycotoxin and its toxicity**

Mycotoxins are low-molecular-weight secondary metabolites produced by various fungal group specially *Fusarium* spp. and are not only toxic to plant causing serious diseases in them but also significantly harmful to human and animals [44]. *Fusarium* is one of the most important plant-pathogenic fungi producing most important mycotoxin. Some of the emerging mycotoxin produced by the *Fusarium* includes: trichothecenes, zearalenones, fumonisins, and moniliformin. These mycotoxins are naturally found to occur in plants and its products all over the world. The

#### *Fusarium Disease of Maize and Its Management through Sustainable Approach DOI: http://dx.doi.org/10.5772/intechopen.100575*

mycotoxins namely: fumonisins, beauvericin, fusaproliferin, and moniliformin produced by the strains of *F*. *verticillioides*, *F*. *proliferatum*, and *F*. *subglutinans* are commonly associated with maize ear rot disease [45].

Fumonisins (FUMs), especially FUM B1 (FB1) produced by *F*. *fujikuroi* species complex in warm climate are extremely toxic and carcinogenic to human causing liver cancers and human esophageal [46–48]. FB1 is also reported to have toxic effects in animals and several organs like kidney, liver, lungs, and nervous and cardiovascular systems [44, 49]. FUMs also exert its toxicity by causing wilting, chlorosis, and necrosis in maize and also interfere with shoot and root growth of the plant [44, 50]. It is evident that FUM phytotoxicity induced some symptomatic diseases in maize seedlings when inoculated with *Fusarium verticillioides* [51]. Trichothecenes (TRIs) are sesquiterpenoids with a tetracyclic ring system, categorized into type A to type D inhibits protein synthesis in eukaryotes and suppress or stimulate immune system [49]. They also produce some common effects on livestock like changes in neuroendocrine, hepatological and gastrointestinal systems; gaining of weight and feeding reduction [52]. Most TRIs have also been reported to produce phytotoxic effects. Reduced seed germination; stunting of coleoptiles, roots, and shoots; chlorosis; wilting; and necrosis are the most common toxic effect of TRIs [52]. Zearalenone (ZEA) produced by the *F*. *graminearum* and the *F*. *incarnatumequiseti* in maize is effectly contaminated to its product and produce severity in their various consumers [44, 53]. Various species of *Fusarium* infecting maize have been reported with some of the emerging mycotoxin (**Figure 2** and **Table 1**).

**Figure 2.** *Chemical structure of some important mycotoxin produced by* Fusarium *spp. [44].*


#### **Table 1.**

*Some of the emerging mycotoxin produced by* Fusarium *spp. in maize.*
