3.2. Zearalenone

Although zearalenone (ZEN) is an important mycotoxin in many cereals, less attention has been paid to control this toxin. ZEN is a potent mycoestrogen which competitively binds to estrogen receptors causing reproductive disorders in farm animals and human [5]. Other forms of ZEN include α and β zearalenol, zearalanone and, α and β –zearalanol which are often detected at variable concentration usually lower than ZEN.

Trichoderma isolates have recently been reported to detoxify ZEN by transforming ZEN into reduced and sulfated forms [165]. This was in accordance with previous results by Gromadzka et al. who tested two isolates of Trichoderma and several isolates of Clonostachys in vitro against two isolates of F. graminearum and two isolates of F. culmorum. Despite the high rate of ZEN reduction (over 96%), the performance of these isolates under greenhouse or field experiments was not confirmed [128].

C. rosea converts ZEN into less toxic compounds through an enzymatic alkaline hydrolysis by lactonohydrolase in vitro [23, 166]. This has been proved after cloning the coding region of the responsible gene, zhd 101, and expressing in Schizosaccharomyces pombe [167] and Escherichia coli, but not with Saccharomyces cerevisiae which exhibited weak detoxification activity against ZEN [168]. Through this approach which involves the direct interaction between BCAs and pathogen toxin, resistance of BCAs to mycotoxin itself is an important feature to ensure the efficacy and durability. Also, it was proven that C. rosea is tolerant to ZEN exposure due to the presence of high numbers of ATP-binding cassette transporters [169].

#### 3.3. Fumonisins

Fumonisin B1 (FB1), the main member of fumonisins, is produced by F. verticillioides and F. proliferatum which usually infect maize [14]. The mycotoxin suppresses ceramide synthase and causes neurological toxicities in horses, pulmonary edema in pigs, and may pose hepatotoxicity and esophageal cancer in human [18]. Therefore, several trials have been conducted to effectively control the mycotoxin in maize using different strategies. Most of the field studies were done using bacterial BCAs [147, 148, 150, 158] while other types of BCAs, and fungi, were restricted to in vitro testing [73, 154–156]. Maize rhizobacterial isolates belonging to Pseudomonas and Bacillus genera significantly reduced the mycotoxin production by 70 to 100% [157]. However, in another study, a mixture of P. Solanacearum and B. subtilis was not able to affect FB1 concentration [151]. Seed treatment with B. amyloliquefaciens Ba-S13 was sufficient to reduce fumonisins B1 concentration in maize field tests [148]. That has been confirmed in a 2-year field study with the same bacteria, B. amyloliquefaciens, after application of two different treatments: inoculating seeds during pre-sowing and maize ears at flowering [150].

P. fluorescens isolated from maize rhizosphere by Nayaka et al. had a clear reduction of FB1 content and the disease incidence after challenge with F. verticillioides during a 3-years study [147]. Seed treatment followed by spray treatment with a pure culture of P. fluorescens reduced the incidence of fumonisins by 88% [147]. Bacon et al. suggested the use of the endophytic bacterium, B. subtilis to control FB1 production as a convenient approach to prevent the vertical transmission of the fungi. Under greenhouse conditions, FB1 was reduced by 50% [154].

When T. viride was co-inoculated in corn kernels with F. verticillioides, a reduction of FB1 by 72–85% was obtained depending on the time of inoculation [73]. The fungus was also proposed as a postharvest agent to prevent the accumulation of the toxins during storage [73, 154]. It was proven that C. rosea can inhibit the synthesis of fumonisins by F. verticillioides but does not degrade it [170]. Constant reduction of FB1 by 60–70% depending on the temperature when a 50:50 mixture of the pathogen and C. rosea 016 applied at different ripening stage of maize cobs. These investigations were done as F. verticillioides may attack maize at ripening under suitable environmental conditions [156]. Previously, similar results at the same concentration (50:50/ pathogen: C. rosea 016) in milled maize agar were also reported [155]. It could be concluded that using bacterial BCAs rely on antibiosis was more effective to control FB1 in vitro and in field trials.
