**2. Materials and methods**

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

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

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

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‐

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

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

non‐staple foods and 1 ppm in uncleaned soft wheat for use in baby foods [3, 4].

content. These two factors are receiving additional attention lately.

were revealed in that study and shown in **Figure 1** of that publication.

reduce the DON content.

days after artificial inoculation.

tion as measures of FHB resistance.

60 Wheat Improvement, Management and Utilization

At the start of the project, large numbers of accession of alien wheat relatives were acquired from numerous gene banks. In addition, cytogenetic stocks and inter‐specific and inter‐ generic hybrids were screened for resistance. Some of the numbers of accessions acquired for screening included 200 accessions of *Triticum monococcum* and 370 accessions of triticales plus lower numbers of other species and hybrids.

The initial screening invariably consisted of inoculation with point inoculation in greenhouses or corn spawn in field plots, followed by scoring of symptoms. In the initial screen, the obvi‐ ous susceptible lines were discarded. Screening on promising lines was repeated. Evaluation of DON content on ground seeds harvested from inoculated plots was carried out on lines that showed minimal scab symptoms.

The lines showing lowest scab symptoms and lower DON content were then crossed to wheat. In most cases, this involved the application of growth hormones following pollina‐ tion, then rescuing of hybrid embryos and culturing on artificial media. In most cases, back‐ crossing to a recurrent parent was necessary to restore full fertility. Screening of progenies from wide crosses was carried out by selecting resistant segregates with minimal symptoms following inoculation. DON contents were determined on lines with minimal symptoms. In some cases, DON contents were determined directly on alien species or cytogenetic stocks following inoculation.

For point inoculation—Type I resistance—plants were grown in controlled environments at day/night temperatures of 20/15°C and 16 hours photoperiods supplied by a combination of florescent and incandescent lamps. Spikes at the 50% flowering stage were point inoculated by injecting 10 μl of a 50,000 spores/ml suspension into a central floret on the spikes. Inoculated plants were retained in a unit maintained at 25°C for 48 hours and 95% RH, then moved to a normal growth cabinet. Symptoms were read at 21 days after inoculation. Symptom scores were expressed as % infected florets. Other symptoms such as blackened rachis were also recorded [12].

Type II resistance was usually evaluated in field plots in the epiphytotic nursery. Where seed quantities were adequate the plots consisted of two 1‐m rows spaced at 6 inches apart and ideally replicated three times. At the boot leaf stages, corn spawn consisting of inocu‐ lated corn and barley seed was spread between the rows at the rate of 80 g/m<sup>2</sup> . Applications were repeated 1 week later. An irrigation system was activated twice a day to maintain a high relative humidity to enhance sporulation of the inoculum. Flowering dates of each plot were recorded, defined as the stage of 50% anthesis. At 21 days after the flowering date, disease incidence and severity was estimated visually for each plot and recorded. FHB indices were calculated from these readings. The plots were hand harvested at physi‐ ological maturity.

Threshing was done with a small plot thresher adjusted to retain the shrunken Fusarium damaged kernels (FDK). Two 1‐g aliquots were removed from each sample and ground in a Wiley mill. To ensure homogeneity of the aliquots, the seed was put through a seed divider.

DON contents were estimated by an ELISA test using established methods [13]. Don contents of plots were expressed as parts per million. The check cultivars in field plots were Roblin as the susceptible check and Sumai3 as resistant. Other checks were selected as those that were parents of the various populations.
