Importance of Semi Quantitative Adventitious Presence (AP) Testing

- Joseph Lopez

It is vital that breeding and seed production programs conduct testing for adventitious presence (AP) of unwanted biotech traits. A properly timed AP test can eliminate the cost of advancing material contaminated with an unwanted biotech trait and provide tangible evidence of a quality seed product.

There are two approaches in determining AP in a seed lot based on the acceptance criteria. Qualitative testing will be used if the acceptance criteria of lot is 0 percent AP. In this case, if any lot is found positive in a qualitative test, the lot will be rejected. If the acceptance criteria of a seed lot is above 0 percent of AP, a quantitative testing is required to determine the percentage of AP in the seed lot.

Quantitative AP testing can be performed in a single bulk seed sample using real time PCR testing. In a seed lot, if the percentage of AP found is equal to or less than the acceptance limit, the lot is accepted otherwise it will be rejected. This method is not used by the industry widely as an error in sampling might reject a potential acceptable lot. EBDI offer a multiple sub-sample (pool) based qualitative testing to quantify the AP contamination in seed lot thus known as semi quantitative AP testing.

Polymerase chain reaction (PCR) technology is used in both the testing methods. In the semi quantitative approach, we divide the bulk seed sample into multiple sub samples (pools), each pool will contain the same number of individual seeds. Pools will be subjected to end point PCR analysis and results as positive or negative pools for the presence of AP. The individual results of each pool will be analyzed using a statistical tool to determine the percent of AP in the seed lot with 95% confidence level.

Seed producers wanting to know the rate of AP contamination, the semi quantitative AP test provides much greater flexibility for statistical analysis to determine the possible upper bound limit of a contamination with 95 percent of confidence level. This information will help the customer to decide on the acceptance of the seed lot. This method reduces the risk of rejecting a good lot since a range of level of AP is acceptable in the current market. By identifying seed lots with AP contamination beyond established limits, a seed producer can avoid the cost of advancing or processing seed lots that are out of tolerance.