**2. The mechanisms involved in enhancing the protective ability of Fusarium strain**

The biological management of Fusarium wilt diseases in soil and crops has been fulfilled by the use of nonpathogenic *Fusarium* spp. and other antagonistic organisms such as *Trichoderma* spp. (*Trichoderma harzianum*, *T. asperellum*, *and T. virens*) (**Figure 1**) [9]. The mechanisms involved in this process are still ill-defined. However, a few hypotheses involved in suppressing the occurrence of pathogenic Fusarium have been made through molecular mechanism elucidation and Fusarium species genome sequencing. Nutrient competition between pathogenic and nonpathogenic fungi has been noticed during the investigation of conducive and suppressive soils as well as population dynamics of soil supplemented with Fusarium spp., and it was revealed that the increase or decrease of Fusarium root colonization and chlamydospore germination were due to the nutrient competition [9, 10].

Competition of infection sites to the root surface was also described as a mode of action between pathogenic Fusarium and saprophytic fungi [11]. Larkin and Fravel investigated the effect of higher glucose concentration (0.2 mg/g of soil) on the germination of chlamydospores of nonpathogenic Fusarium (F047); it was noticed that the higher concentration of glucose suppressed the germ tube elongation of wilt Fusarium pathogen while inhibiting chlamydospore germination [12]. More research has correctly observed that nonpathogenic and pathogenic isolates

#### **Figure 1.**

*The modes of action of the protective strains of F. oxysporum and many other beneficial microorganisms.*

#### *Fusarium Soilborne Pathogen DOI: http://dx.doi.org/10.5772/intechopen.100597*

of Fusarium generally colonize root zones (emergency site of secondary roots, root apex, and elongation zone); these sites have higher nutrient oxidation [2, 10]. There is evidence that nonpathogenic *F. oxysporum*, which is characterized among endophytic fungi, can stimulate the defense response of host plants when plant pathogens attach them; furthermore, it has been found to increase resistance to environmental stress and enhance the production of essential hormones such as auxins and gibberellins, which are known to activate the plant growth [11, 13, 14].

The inoculation of nonpathogenic Fusarium strains into the roots of plants was found to inhibit the disease expression through a systemic resistance induction [15]. Nonpathogenic *F. oxysporum* were inoculated into watermelon plants to test their resistance against pathogenic Fusarium strains, and it was found to cause local and systemic resistance. In addition, the occurrence of both pathogenic and nonpathogenic strains on the root stimulated resistance mechanism in plants, therefore demonstrating their importance in the induction of local resistance [11].
