Scientific opinion on a quantitative pathway analysis of the likelihood of Tilletia indica M. introduction into EU with importation of US wheat

The European Commission requested EFSA to provide a scientific opinion on the USDA APHIS quantitative
pathway analysis on likelihood of Karnal bunt introduction with importation of US wheat for grain into EU and
desert durum wheat for grain into Italy. EFSA was also requested to indicate whether the US bunted kernel
standard would provide equivalent protection against introduction of Tilletia indica into EU, compared to the
existing EU import requirement. The Panel on Plant Health reviewed pathway scenarios, model and parameters
and found several shortcomings regarding model equations and parameter values, particularly a lack of scientific
evidence for the infection threshold. Simulations were computed, for importations of US wheat into EU and
desert durum wheat into Italy, based on original model and an updated model with revised parameter values.
Model output was teliospores number per hectare on soil surface of each EU country. Simulated teliospores
numbers entering EU were lower with the updated than with the original model. These results showed a high
uncertainty, underestimated with the original model, over the number of teliospores entering each EU country.
Sensitivity analysis showed several key parameters (proportion of bunted kernels in Arizona regulated counties,
number of Arizona positive hectares and number of teliospores per bunted kernel) strongly influencing number
of teliospores entering the EU. In addition, high sensitivity indices were obtained with the updated wheat model
for several parameters related to EU country characteristics. Further research is needed to refine parameter
values, to reduce uncertainty and to determine relationship between teliospores number on soil surface and
number of bunted kernels resulting from infection of a wheat plant. The Panel concluded that the US bunted
kernel standard does not provide a level of protection equivalent to EU requirements and that such level of
protection could only be warranted by measures which include testing at harvest and before shipment to detect T.
indica teliospores.