**2.4. Host-plant resistance**

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

Genetically modified crops are plants of which the DNA has been altered through the introduction of a foreign gene to express a trait not inherent to the modified plant. Three transgene-mediated strategies have been proposed for the management of mycotoxigenic fungi and mycotoxins in maize [48]. These include (1) the reduction of fungal infection, (2) the degradation of mycotoxins and (3) interfering with the mycotoxin biosynthetic pathway. To reduce infection by the fungus, the incorporation of antifungal and/or resistance genes, as well as the overexpression of defence-related genes, is required. Catabolic enzymes from microbes have been used to detoxify certain mycotoxins both *in vitro* and *in situ*, before they accumulate in the plant [49–51]. Fumonisin esterase and amine oxidase genes encoding FUM-degrading enzymes have been identified in *Exophiala spinifera* de Hoog and Hasse [48]. None of these genes have, however, been successfully introduced into maize. Maize plants have, however, been genetically engineered to interfere with the biosynthesis of AF and TCT [52, 53]. The best-known example of using genetically modified maize for reducing FER and FUM contamination of grain is Bt maize [54, 55]. This is due to the close association between kernel damage by insects and infection by *F. verticillioides* [56]. Bt maize plants that prevent insect damage, therefore, also reduce FUM contamination of maize grain. Genetically modified maize is not authorised in all

countries and, consequently, conventional breeding efforts are still commonly used.

Exposure of seeds or other heritable materials to chemicals or radiation with the purpose to induce DNA changes (mutations) is known as mutation breeding. Nuclear technology for crop improvement makes use of ionising radiation, which causes induced mutations with a

implementing MAS [39–47].

44 Mycotoxins - Impact and Management Strategies

*2.3.1. Genetic modification*

*2.3.2. Mutation breeding*

**2.3. Unconventional breeding strategies**

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 alternatively exhibiting tolerance in specific environments.

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 FUM than its non-modified isolines [54].
