**2.2. Conventional breeding strategies**

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 determined for each crop and fungal pathogen, respectively.

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 may be strong deterrent factors.

Quantitative trait loci (QTL) associated with resistance to mycotoxigenic fungi has been mapped in maize and wheat and can be used for marker-assisted selection [15, 16, 32–36]. Some QTLs, however, displayed pleiotropic effects, sometimes resulting in resistance to both traits [15, 32, 37]. QTL analyses have also demonstrated pleiotropic effects for resistance to other mycotoxigenic fungi and/or their associated mycotoxins. In QTL studies involving multiple ear rot pathogens, maize resistant to FER and FUM accumulation was also resistant to *F. graminearum* and/or *A. flavus*, with common loci for ear rots and FUM, respectively [15, 37, 38]. Research revealed that some of the genes involved in resistance to FER and Aspergillus ear rot (AER) of maize caused by *A. flavus*, as well as their associated mycotoxins (FUM and AF, respectively), were identical or genetically linked [38]. These studies highlighted common genes and/or resistance mechanisms to multiple mycotoxigenic fungi, demonstrating the potential for breeding resistance to one type of mycotoxigenic fungus, and its mycotoxin may lead to similar responses among other mycotoxigenic fungi and associated mycotoxin. The value of marker-assisted selection for improving Fusarium head blight resistance in wheat has been confirmed by numerous researchers and success stories from breeding programmes implementing MAS [39–47].

high mutation frequency in plants [57]. These mutations might be beneficial and alter physiological characters of plants, including plant height, ear height and improved root architecture [58, 59]. The radiation of seeds may also cause genetic variability that enables breeders to select new genotypes with improved grain yield and quality [60]. Mutation breeding has been successfully used to generate genetic variation in cereal crops, including maize, for a number of aspects including enhanced yield and productivity, altered ear length, drought tolerance and enhanced stem structure [61–63]. It can thus potentially provide an attractive means for

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

http://dx.doi.org/10.5772/intechopen.76808

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The planting of disease-resistant plants is an effective, affordable and environmentally sound strategy to control ear rot diseases and mycotoxin accumulation [64]. Commercial hybrids differ in their ability to accumulate mycotoxins [64], while hybrids grown outside of their adapted range are more susceptible to mycotoxins than those grown within their adapted range [18]. Determining host-plant resistance to mycotoxigenic fungi and mycotoxin accumulation is a fundamental step towards developing commercially tolerant plant varieties. Several factors require careful consideration when screening materials for resistance to mycotoxigenic fungi and their mycotoxins. Inoculation technique significantly contributes to the efficacy of the screening protocol and should, therefore, be appropriate, produce consistent results and consider the disease cycle of the pathogen. Numerous studies relating to different crops report on the importance of screening for resistance under variable environmental conditions since genotype by environment interactions (GEI) plays such a vital role in disease development and mycotoxin contamination. Furthermore, GEI and stability indicators provide for the selection of material tolerant across a broad range of environments or alterna-

Various countries have reported on the tolerance levels of maize and wheat cultivars to mycotoxigenic fungi and associated mycotoxins [65–67]. However, focus has been placed on the characterisation of inbred lines for the identification of appropriate breeding material towards resistance to mycotoxigenic fungi and their toxins [68–74]. Genetically modified maize, expressing *Bacillus thuringiensis* genes (BT maize), has been found to accumulate less

Adhering to planting dates and planting plants at lower or optimal densities reduces mycotoxin accumulation during production [75–77]. Plants should be planted at recommended row widths and densities to specifically reduce water stress [78] and ensure optimal nutrient availability. Maize ears should be harvested from the field as soon as possible because favourable conditions for ear rot and/or mycotoxin accumulation may occur if harvest is delayed,

generating tolerance to mycotoxigenic fungi and their mycotoxins.

tively exhibiting tolerance in specific environments.

FUM than its non-modified isolines [54].

*2.5.1. Planting recommendations*

**2.5. Cultural preharvest management strategies**

thus leading to elevated mycotoxin levels [79, 80].

**2.4. Host-plant resistance**

#### **2.3. Unconventional breeding strategies**
