Selenium enriched potatoes. Bag of potatoes (Solanum tuberosum) that contain a high level of selenium (Se) - 0.009 mg per 100g. These have not been genetically modified but the selenium is introduced either by using a specialist fertiliser or adding selenium to the water used to feed the crop. Selenium is a trace element found in many foods, which helps our immune system fight viruses. It is the soil that determines the selenium content. However, certain areas such as Australia and Ireland tend to be deficient.