**1. Introduction**

Fusarium head blight (FHB) is a ubiquitous fungal disease of wheat, barley, oats, rye and ear rot of maize. Deoxynivalenol (DON) is a secondary metabolite of Fusarium head blight. DON content renders the harvested grain unsuitable for food or feed. It can cause malfunc‐ tion of respiratory, immune and even reproduction systems. It has been estimated that for

© 2017 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. © 2017 Her Majesty the Queen in Right of Canada, as represented by the Minister of Agriculture and Agri-Food Canada. 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.

each 1 ppm increase in DON content in harvested grain, feed consumption in swine decreases by 7.5% [1, 2]. Additional costs are incurred in lowering the DON level of threshed grain. In North America, the US‐FDA has set tolerance limits for DON of 1 ppm in processed grain [1, 2], whereas Health Canada has set regulations of 2 ppm in uncleaned soft wheat for use in non‐staple foods and 1 ppm in uncleaned soft wheat for use in baby foods [3, 4].

In an epidemic year such as 1966 in Southwest Ontario in Canada, samples of winter wheat taken directly from farmer's combine showed a range in DON content of 1.1–13.9 ppm [5]. These findings point to the fact that genetic resistance must be put into the wheat crop to reduce the DON content.

In terms of breeding for resistance to FHB, earlier efforts were focussed on accumulating genes that reduced the symptoms of Type I and Type II resistance. Bai [5] was among the first to consider the inheritance of two other traits, Fusarium damaged kernels (FDK) and DON content. These two factors are receiving additional attention lately.

The correlation between FDK and DON is in the order of 0.81 [6] but they are much lower for incidence/severity and DON content, indicating that FDK and DON deserve additional atten‐ tion as measures of FHB resistance.

Somers et al. [7, 33] were the first to suggest that DON accumulation was controlled by inde‐ pendent quantitative trait loci (QTL). These QTL were located on chromosome 5A, on 2D (coincident with a plant height QTL) and on chromosome 3BS (coincident with a QTL for Type I resistance). In addition, a number of minor QTL that were not specifically mapped were revealed in that study and shown in **Figure 1** of that publication.

**Figure 1.** Resistance to Fusarium head blight in an accession of *Triticum monococcum*. Disease symptoms developed at 21 days after artificial inoculation.

This was followed by similar reports [8, 9, 10]. In the latter study, a major QTL for DON con‐ tent was mapped on chromosome 2AS that was independent of FHB severity. The cultivar CJ9306 was the source of several QTL for resistance to DON accumulation [11]. Two new QTLs were reported, in that study QFhs.nau‐2DL and QFhs.nau‐1AS, whereas two others, QFhs.ndsu‐3BS and QFhs.nau‐SAS, were validated in that study.

This overview will discuss the variability for DON content in alien relatives of wheat and in progenies obtained from wide crosses with wheat.
