Methods and issues regarding detection of deoxynivalenol, Fusarium-damaged kernels, and Fusarium spp. in commercial grain in Canada

The Canadian grain industry uses visual estimation of Fusarium-damaged kernels (FDK) for grading, but this method does not always accurately predict deoxynivalenol (DON) levels in specific lots. The imminent introduction of lower limits for DON in wheat and the increasing trend of producers and grain companies to market wheat directly, with DON limits specified in contracts, are challenging the methods now applied to measure or estimate the DON levels in wheat. Among the detection methods reviewed for the grain trade, image analysis and near infrared spectoscopy are the most attractive because they are nondestructive, simple, and have multiple applications. However, the adoption of these methods may be restricted by capital cost and their limit of detection. Both methods estimate DON indirectly, from other Fusarium parameters, and neither is commercially proven. The problem with near-infrared spectoscopy is that it measures factors associated with the presence of DON, such as kernel hardness and color, which are not exclusive to the presence of DON. Image analysis has the advantage of measuring FDK objectively, but also suffers from the shortcomings of estimating DON indirectly, by FDK. If the new DON limits proposed are adopted, these will be near the limit of detection of the immunomethods commonly employed for measuring DON. Although immunomethods require laboratory facilities, more time, and technical skills and may not account for other Fusarium factors that affect grain quality, they require only a low capital investment, are reasonably priced, and have wide acceptance in the trade. Immunomethods that target the fungus to genus or species can be designed as either qualitative or quantitative, and some DNA-based kits are now commercially available. Quantitative methods provide a better estimate of toxin levels resulting from the growth of Fusarium spp., and of their effects on grain quality, but the measure remains an approximation that relies on the strength of the relationship between the fungal content and DON level. Ultimately, the methods chosen will be determined by guidelines for DON, here and abroad, the purpose of the testing, and the needs of each sector of the grain industry; more than one method may be appropriate.