Estimating mycotoxin contents of Fusarium-damaged winter wheat kernels

Winter wheat (Triticum aestivum L., cultivars Ritmo and Dekan) grain was sampled in Northern Germany between 2001 and 2006. Kernels damaged by fungi of the genus Fusarium were separated from sound grain by visual assessment. Samples containing 0%, 20%, 40%, 60%, 80% and 100% of Fusarium-damaged kernels were compiled and analyzed for the Fusarium type B trichothecenes deoxynivalenol (DON, 2001-2006), nivalenol (NIV, 2006), 3-acetyl-deoxynivalenol (3AcDON, 2006) and 15-acetyl-deoxynivalenol (15AcDON, 2006). The relationship between mycotoxin contents and the percentage of Fusarium-damaged kernels was calculated for each lot of grain. Apart from one exception, relationships between the percentage of Fusarium-damaged kernels and NIV, 3AcDON or 15AcDON were non-significant. In contrast, close relationships between the percentage of Fusarium-damaged kernels and the DON content were observed (r(2)=0.93-0.99). The y-axis intercepts were not significantly different from zero, but the DON content of the damaged kernels varied by a factor of 11.59 between years and by a factor of 1.87 between cultivars. Fusarium-damaged kernels contained between 0.21 and 2.39 microg DON kernel(-1). The overall average DON content of a Fusarium-damaged wheat kernel was 1.29 +/- 0.11 microg. The DON content of diseased kernels was affected by environment and wheat genotype but not by genotype x environment interaction. On average, Fusarium-damaged kernels contained 9.7-fold more DON than 15AcDON, 19.5-fold more DON than NIV, and 26.9-fold more DON than 3AcDON. 3AcDON and 15AcDON contents per wheat kernel were not significantly different between cultivars. On average, 4.27% of Fusarium-damaged kernels were sufficient to reach the 1.25 mg DON kg(-1) grain limit for unprocessed cereals in the EU. Given the low percentages of Fusarium-damaged kernels that are equivalent to current legal DON limits, grading accuracies >96% would be needed when using automatic grading systems for separating sound from damaged kernels.