Statistical considerations in seed purity testing for transgenic traits

Recent advances in agricultural biotechnology have produced many new crop v arieties with valuable transgenic traits. These varieties are being, and wi ll continue to be, marketed alongside conventional nontransgenic varieties. As a result, seed purity in commercial seed lots is of particular importan ce to both seed consumers and seed producers. A key step in the seed produc tion process is the design of sampling and testing procedures used to evalu ate seed lot purity. However, due to uncertainties in such methods, there i s always a risk of incorrectly rejecting or accepting a seed lot. This pape r discusses factors that should be considered when designing and implementi ng seed purity testing procedures to manage this misclassification risk - e specially with regard to the presence or absence of transgenic traits. Many sources of uncertainty in both seed lot sampling and in the assay methods are described, and recommendations for reducing their impact are provided. This paper also explains the statistical concepts of misclassification risk as it affects seed producers and seed consumers. Sampling plans and formul as for determining the sample sizes necessary to control these misclassific ation errors when accepting or rejecting seed lots are also provided. Both simple, single-stage testing plans and the, often more efficient, double-st age testing plans are described. Testing seed pools rather than individual seeds is introduced as another way of adding efficiency to the testing proc ess. Formulas are given for determining, from a seed sample, the confidence limits for the actual purity level of a commercial lot.