**1. Introduction**

The contamination of food and feed crops with mycotoxigenic fungi is a persistent problem contributing to food safety and security worldwide. The infection of crops by these fungal pathogens

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

affects crop yield and quality but of greater concern are the secondary metabolites they produce, collectively known as mycotoxins. Ingestion of mycotoxin-contaminated products has been associated with a wide range of noxious effects on humans and livestock. The major food and feed crops affected by mycotoxigenic fungi and mycotoxins include rice, maize, wheat, soybean, sorghum and groundnut, although several other crops are also affected. The association of these crops with mycotoxigenic fungi is ubiquitous, and crops are affected wherever they are produced. Three major groups of mycotoxigenic fungi are associated with mycotoxin contamination namely *Aspergillus*, *Fusarium* and *Penicillium*. They each produce a number of mycotoxins, but six mycotoxins have been studied extensively and are considered among the most important and they include the aflatoxins (AF), fumonisins (FUM), trichothecenes (TCT), zearalenone (ZEA), ochratoxin (OT) and patulin (PAT). Mycotoxin contamination levels in food and feed crops have therefore elicited numerous countries to institute regulations regarding the maximum permissible levels of these mycotoxins in unprocessed and processed products.

**2.1. Tolerance to mycotoxigenic fungi**

tion of wheat [21–23].

**2.2. Conventional breeding strategies**

may be strong deterrent factors.

determined for each crop and fungal pathogen, respectively.

Crops with resistance to numerous mycotoxigenic fungi have been documented [10–12], but none of these are immune. Resistance to mycotoxigenic fungi therefore appears to be quantitative rather than qualitative. Breeding programmes at both public and private institutions are initiating and expanding their efforts to develop disease-resistant inbred and hybrid materials [13]. A number of international institutions such as the International Maize and Wheat Improvement Centre (CIMMYT) and the International Institute of Tropical Agriculture (IITA) in African countries including Kenya and Nigeria have established breeding programmes with the primary focus on producing inbred lines with improved resistance to *A. flavus* and AF. The development of tolerant cultivars, however, has been slow due to the polygenic, quantitative nature of resistance to mycotoxigenic fungi [14–17], the unavailability of immune germplasm [11, 15] and the effect of the environment on disease development and mycotoxin production [18–20]. The development of tolerant varieties, therefore, may be a long (8–10 years) and costly process that needs to be conducted as effectively as possible. Little to no commercial plant crop, completely resistant to mycotoxigenic fungi and mycotoxins, has been produced by conventional breeding, with the excep-

Preharvest Management Strategies and Their Impact on Mycotoxigenic Fungi and Associated Mycotoxins

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Diallel analysis to determine the general combinability (GC) and specific combinability (SC) of resistant genotypes has been reported for *Aspergillus* and *Fusarium*, mostly performed on maize [24–27] and wheat [28–30]. The response of an inbred line to *F. verticillioides* and FUM, and the corresponding GC in hybrids, was significantly correlated. This indicates that an efficient way to improve resistance to *F. verticillioides* and FUM in maize hybrids, specifically, is to first evaluate and select resistant inbred lines that can be used to develop resistant hybrids [24]. This was also demonstrated for breeding resistance to Fusarium head blight (FHB) of wheat [30]. Maize hybrid performance for resistance to *F. graminearum* could, however, not be predicted based on the GC of inbred line parents [27]. Therefore, this relationship needs to be

Inbred lines with resistance to aflatoxin contamination were evaluated for GCA and SCA for resistance to fumonisin accumulation, and two lines with resistance to FUM and AF were registered [25]. That research demonstrated the ability to breed resistance to multiple mycotoxigenic fungi and/or their mycotoxins. Furthermore, improved resistance to *F. verticillioides* and FUM in inbred lines derived from cross-pollination of resistant and elite maize lines has been demonstrated [31]. The subsequent hybrids produced from the crossing of improved lines with elite lines, however, did not demonstrate an improved activity against Fusarium ear rot (FER) and FUM accumulation, although some improved lines performed well as an inbred line and as a component of a hybrid [31]. To date, little to no research is reported on the development of tolerant varieties using recurrent selection breeding methods. Considering that resistance to mycotoxigenic fungi is polygenic and quantitative, recurrent selection presents a feasible breeding strategy; however, time and cost involved in this breeding strategy

More than 100 countries have established mycotoxin regulations, including 15 African countries [1–3]. The European Union and United States Food and Drug Administration established maximum allowable levels for certain food contaminants, including mycotoxins, with the aim to reduce their presence in foodstuffs to the lowest levels reasonably achievable by means of good manufacturing or agricultural practices [4]. Most of the countries have mycotoxin regulations for at least AFB1, produced predominantly by *Aspergillus* spp., to aid in minimising food safety concerns. Although fewer countries regulate *Fusarium* mycotoxins, a marked increase in the regulation of this mycotoxin has been observed recently. These regulations have globally significant implications for the importation and exportation of products. Regulatory infrastructure, however, does not enable inspection and enforcement [5], making the regulatory control of mycotoxins in Africa largely ineffective [6].

The management of mycotoxigenic fungi and their subsequent mycotoxins is therefore vital towards ensuring sustainable, safe food and feed production. Integrated management practises that reduce the incidence of mycotoxigenic fungi as well as the management of abiotic factors that contribute to mycotoxin contamination are required before and following harvest. However, preharvest management is considered the most important in limiting the overall contamination of crops. Therefore, the use of tolerant varieties is deemed the most proficient and environmentally sound approach to manage fungi and their toxins. In addition, several other management approaches such as optimal plant production, cultural practises, chemical control and the management of mycotoxigenic fungi by atoxigenic strains or bacteria could further reduce fungal incidence and subsequent mycotoxin contamination.
