Comparison of Sampling Strategies to Evaluate Rate of Transgenic Adventitious Presence in Agricultural Fields

Abstract

Methods have been developed to detect transgenic presence in non-GM maize fields. These detection methods may be used to determine whether the regulatory transgenic rate threshold (0.9%) is exceeded, but the results are likely to depend on the grain sample size and on the sampling strategy used to collect grains within agricultural fields. Until now, no clear sampling strategy and sample size have been defined for implementing detection methods. This study aims to compare four types of sampling strategies for maize grains in agricultural fields -- i) random sampling, ii) systematic sampling, iii) stratified sampling, and iv) regression sampling. The first approach simply randomly samples maize ears in the considered field. The second approach consists of selecting ears according to a regular grid. The two final approaches use an auxiliary variable correlated with the real transgene distribution in order to define strata with contrasted presence rates or to reweight a sample of ears selected at random.