Which of the following is an example of pathogen-free seed?

The concept of pathogen-free seed is crucial in ensuring healthy plant growth and preventing the spread of diseases. In this context, an example of pathogen-free seed is represented by lettuce for dodder control. Dodder is a parasitic plant that can severely impact crops, and using pathogen-free seeds involves selecting seeds that have been confirmed to be free from the pathogen that can lead to dodder infections.

Using pathogen-free seeds helps in maintaining healthy crops and can reduce the need for chemical interventions later in the growing cycle. Lettuce that is specifically chosen and bred to be free from dodder ensures that the plants can establish themselves without interference from this harmful parasitic species.

In contrast, while tomatoes grown in greenhouses can be managed to mitigate disease risks, the context does not specifically define them as pathogen-free. Similarly, treating wheat with fungicides helps control existing pathogens but does not guarantee the seeds are free from pathogens prior to treatment. Lastly, fruits grown in the same field do not directly relate to the concept of pathogen-free seeds, as the field environment can harbor various pathogens that can affect different crops after planting.