3.4. Aflatoxins

content was achieved when B. subtilis RC 218 and Brevibacillus spp. RC 263 were applied at anthesis for two seasons [144] which was consistent with previous findings under greenhouse conditions by the same authors [163], although there was no constant reduction in the disease incidence. Opposite to that, Khan and Doohan tested three strains of Pseudomonas spp., two strains of fluorescens and one strain of frederiksbergensis, against F. culmorum and DON production in wheat and barley in a small scale field experiment. The results showed that DON was

Other types of trichothecenes were not well researched as the previously mentioned toxins due to their low incidence in crops. Variable results for T-2 toxin after spraying the ears of susceptible and resistant wheat cultivars with Trichoderma spp. under greenhouse conditions were documented. The author used four fungi, Epicoccum spp., Trichoderma spp., Penicillium spp. and Alternaria spp. however the last one is known for production of Alternaria toxins [107].

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

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

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

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

reduced in wheat and barley by 12 and 21%, respectively [164].

often detected at variable concentration usually lower than ZEN.

presence of high numbers of ATP-binding cassette transporters [169].

3.2. Zearalenone

70 Mycotoxins - Impact and Management Strategies

was not confirmed [128].

3.3. Fumonisins

AFs are the most natural carcinogenic substance in the history targeting mainly liver and are classified as Group 1 according to the International Agency for Research on Cancer [4, 6, 16, 171]. A. flavus and A. parasiticus infect mostly groundnuts, maize, cottonseed, soybean and tree nuts in the field and/or during storage producing a wide range of secondary toxic metabolites including AFs [60, 172]. Researchers have mostly been focusing on A. flavus as the fungus is highly invasive and more widespread in nature compared to A. parasiticus. Regarding their ability to synthetize mycotoxins, toxigenic A. flavus strains produce aflatoxin B1 (AFB1) and B2 (AFB2) while A. parasiticus produces four types of AFs (AFB1, AFB2, AFG1 and AFG2). CPA is only produced by A. flavus including strains which lack the potential to produce AFs [173].

In general, reduction of AFs in different crops has mostly been performed with nontoxigenic A. flavus strains [27, 52, 54, 60, 65, 114, 120, 123]. Some of these strains (AF36 as an example) are commercially available in the market [53, 65]. Two theories are suggested on the mode of action for the reduction of AFs by non-toxigenic A. flavus BCAs; (i) reduction due to competitive exclusion on toxigenic wild A. flavus population and (ii) inhibition of biosynthetic pathways involved in aflatoxin production, however the exact mechanism is still obscure [62].

Doster et al. used A. flavus strain AF36 as a BCA to control AFs in pistachio orchards for four consecutive seasons (2008–2011) and he could diminish AFs level by 20–45% [114]. In groundnuts, more trials in vitro [61, 66] and in the field [58–60] have been done. Zhou et al. 2015 found a positive correlation between AFs reduction rate and inoculum dose while Hulikunte Mallikarjunaiah et al. 2017 measured total AFs in rhizospheric and geocarpospheric soil and groundnut seeds after he treated them with two strains isolated from India. A significant reduction of mycotoxin concentration below the maximum permissible levels for ground nuts was obtained [61]. Field trials in Argentina were designed to control AFs in groundnut. However, the author reported a high level of AFs reduction, and the results were inconsistent between the two seasons [58, 59].

delivery (conidial or spore suspension/with or without carrier), application time (during seeding or flowering) and application route (to the soil or directly to the seed) to ensure the interaction of BCAs against the pathogen. Examples for the available BCAs in the market include AF36 and Afla-Guard® which are commercial BCAs for pre-harvest application to control aflatoxin contamination in the United States [62], Polyversum®, a recent authorized commercial product in France (Pythium oligandrum strain ATCC 38472) to be used against Alternaria spp., Fusarium spp., and other plant pathogens, and Plant ShieldTM which is the

Biological Control of Mycotoxigenic Fungi and Their Toxins: An Update for the Pre-Harvest Approach

http://dx.doi.org/10.5772/intechopen.76342

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It is crucial to test all the application related parameters in the field as these parameters may give significantly variable results which are not usually followed in many of the performed field trials against mycotoxigenic caused diseases. For example, point inoculation of Streptomyces sp. BN1 was not effective to control FHB in wheat while spraying of bacterial spores during wheat flowering gives better results [175]. Successful formulation of C. rosea ACM941 guaranteed its efficacy to control FHB in corn, soybean and wheat under filed conditions [176], while most of the field trials used a conidial or spore suspension of the BCAs which may give variable and inconsistent results. Ear inoculation with B. amyloliquefaciens and Enterobacter hormaechei exhibit highly changeable results while treatment of seeds showed more stable results for managing F. verticillioides infection and toxin content in maize [150]. On the other hand, B. subtilis strains SB01, SB04, SB23, and SB24 were performing better to control root rot disease when they were applied to soil than treatment of soybean seeds [145]. Omitting one or

In some cases, a mixture of two more BCAs maybe advisable in the field for a better disease control in case they have a synergistic effect. For example, mixture of L. plantarum SLG17 and B. amyloliquefaciens FLN13 showed more efficacy in controlling FHB in wheat durum [131].

Although the field trials are exhausting and time consuming, it should consider the application way, application time, effective dose and the best formula in order to precisely evaluate the performance of the selected BCAs and thereafter ensure an effective control of the mycotoxi-

An important obstacle in the commercialization of BCAs is legislation. Current legislations in Europe classify BCAs as Plant Protection Products/Pesticides and hence they must follow the according regulations of the pesticides. This entails that for each BCA the mode of action must

Despite the considerable amount of research that have been done to screen and select effective BCAs to control mycotoxigenic pathogens and their mycotoxins, still there are several pitfalls for using BCAs. For instance, the broad spectrum antagonistic activity of some BCAs such as Trichoderma spp., against several pathogenic fungi may also affect other beneficial organisms present in rhizosphere [178] and this may require more research for target specific BCAs. Even though implementation of a biological control strategy is strongly recommended to replace the

more of the above parameters may lead to misevaluation of the selected BCAs.

registered product for T. harzianum 22.

genic fungal infection and their mycotoxins.

be documented and their use should be rational [177].

5. Conclusions and future perspectives

High levels of AFs and CPA control in maize field were achieved after challenging two strains of A. flavus with atoxigenic strains K49 and NRRL 21882 [65]. Mauro et al. could obtain similar results in vitro after screening for local atoxigenic strains from Italy [67]. In Nigeria, a successful maize field trial exhibited the promising use of two locally isolated strains, La3279 and La3303, in controlling AFB1 and AFB2 up to 99.9% [120]. When these two strains mixed with other two strains to make a mixture applied to the soil before flowering, a similar conclusion was obtained [55] with the advantage of persistence of the biocontrol effect during storage.

Researchers have also tested different species of Trichoderma such as T. viride, T. harzianum and T. asperellum [38, 95, 115, 116]; bacteria [84, 121, 124]; yeast [36, 174]; and algae [118] as a potential alternative BCAs to control Aspergillus spp., although not all have looked into mycotoxins (Figure 2B). Production of two volatile compounds, dimethyl trisulfide and 2,4-bis(1,1 dimethylethyl)-phenol, by Shewanella algae strain YM8 showed a 100% inhibition on aflatoxin synthesis in maize and peanuts stored at different water activities [118]. Previously, B. subtilis RCB 90 in vitro was also reported to completely inhibit AFB1 [121]. The yeast, Candida parapsilosis IP1698 was also able to inhibit aflatoxin production (90–99%) at different pH and temperatures [174]. This was also in line with the same reduction percentage obtained but with Bacillus spp. P1 and Bacillus spp. P11 [40]. Aiyaz et al. tested in the field, four BCAs and all the formulations, by maize seeds treatment application, had a significant reduction in AFs level [95].
