3.1. Trichothecenes toxins

Mode of action of BCAs

for niche / nutrients

Wheat ✓ [126]

Sorghum ✓ [126] Wheat ✓✓ ✓ [126, 127]

Rice ✓ ✓✓ [133]

Sorghum ✓ [126] Wheat ✓ [126]

Sorghum ✓ [126]

Soybean ✓ ✓✓ [145]

Sorghum ✓ [126] Wheat ✓ [126]

Sorghum ✓ [126] Wheat ✓ ✓✓ ✓ [107, 126, 127]

Wheat ✓ ✓ [129]

Sorghum ✓ [126] Wheat ✓ [126]

Sorghum ✓ [126] Wheat ✓✓ ✓ [126, 127]

Wheat ✓ ✓ [127]

Sorghum ✓ [126] Wheat ✓✓ ✓ [78, 126]

Maize ✓ ✓✓ ✓ [73, 84, 90, 94–96, 146–158]

Maize ✓ ✓ [72, 127–129] Wheat ✓ ✓✓ ✓ [48, 51, 130–132]

Maize ✓✓ ✓ [99, 128, 129, 134]

Wheat ✓ ✓✓ ✓ [35, 48, 51, 72, 76–78, 89, 93,

avenaceum Maize ✓ [126]

culmorum Barley ✓ ✓ [92, 102]

equiseti Maize ✓ [126]

graminearum Barley ✓ [103]

langsethiae Wheat ✓ ✓ [127] nivale Maize ✓ [126]

poae Maize [126]

proliferatum Maize ✓ ✓ [129, 146]

sambucinum Maize ✓ [126]

sporotrichioides Maize ✓ [126]

verticillioides Rice ✓ ✓ [74]

crookwellense Maize ✓ [126]

Table 1. Different modes of action used by BCAs against mycotoxigenic fungi.

Indirect through the plant References

100, 101, 107, 108, 126, 127, 129–131, 135–144]

Pathogen Host Mycoparasitism Antibiosis Competition

68 Mycotoxins - Impact and Management Strategies

Fusarium head blight (FHB) and Fusarium ear rot (FER) are two of the most serious diseases affecting wheat and maize respectively throughout the world [130, 131, 139]. Over the last few years, FHB was predominantly caused by three species of Fusarium: F. graminearum, F. avenaceum and F. culmorum [108, 159] while FER is mainly caused by F. verticillioides, F. proliferatum, F. subglutinans, and F. graminearum [154, 156]. However FHB mostly occurs as a complex of several species [14, 160]. Each disease has multi-destructive effects on the crop through reducing the yield and grain quality. Over 180 types of trichothecenes are produced by Fusarium spp. contaminating mainly agricultural staples such as maize, wheat, and barley [14, 15]. The most prominent members are deoxynivalenol (DON), nivalenol (NIV) and T-2 Toxin. The biochemical importance of DON for fungal growth and development is not fully clear yet; however, it may have an important role during fungal infection and colonization and act as a virulence factor [160]. In animals, DON interferes with the cellular protein synthesis and clinically causing animal feed refusal and vomiting while NIV may induce genotoxic effect and leucopenia on long term exposure [4, 5, 17]. T-2 toxin triggers apoptosis to immune cells [161]. Due to the complexity of the life cycle of Fusarium spp., researchers mostly tried two application strategies to biologically control the disease, treatment of the crop residue with the antagonist or treatment of wheat ears at anthesis [162]. Most of the performed experiments used bacterial BCAs rely on antibiosis mainly to control the diseases and DON level. Less research discussed the effect of BCAs on NIV [51] and T-2 toxin [107].

An isolate of Trichoderma, T. gamsii 6085, was selected as a potential antagonist against F. culmorum and F. graminearum. The strain exhibited the capacity to negatively affect DON production by both pathogens up to 92% [72]. A field experiment on winter wheat for two seasons was conducted to evaluate the efficacy of different BCAs against ear blight and associated DON presence. Two strains of F. equiseti were the best performing strains and decreased the mycotoxins level produced by F. culmorum and F. graminearum by 70 and 94%, respectively. However, low levels of NIV in the cereals treated with F. equiseti were detected [51]. Recently, Piriformospora indica has proven its promising ability to reduce the severity the disease caused by F. graminearum and mycotoxin DON contamination in wheat by 70–80% and increase the total grain weight of F. graminearum-inoculated samples by 54% [100]. Novel bacterial endophytes predicted to be Paenibacillus polymyxa and Citrobacter were able to detoxify DON in vitro, but the performance of some of these isolated strains under field condition or in green house has not been reported yet [99].

Three stains of the yeast Cryptococcus spp. (Cryptococcus nodaensis OH182.9, Cryptococcus spp. OH 71.4, and Cryptococcus spp. OH 181.1) were tested in several field experiments and they could control the disease by 50–60% on susceptible winter wheat. However DON content was the same as control [137]. Later, the same group cultivated another strain, Cryptococcus flavescens OH 182.9, and applied it at early anthesis but found no effects on DON level [142].

Besides fungal and yeast BCAs, bacteria have also been used to control DON produced by F. graminearum in wheat [35, 139, 144, 163] and in maize [99]. A complete reduction in DON 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 reduced in wheat and barley by 12 and 21%, respectively [164].

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:

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

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

71

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

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

inoculating seeds during pre-sowing and maize ears at flowering [150].

in vitro and in field trials.

3.4. Aflatoxins

still obscure [62].

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].
