The lab does research in a variety of settings
In the greenhouse
We run some experiments in the greenhouse because it is easy to control conditions of an experiment in there. We can be sure each plant gets exactly the amount of water and nutrients we want it to, and we know all the plants live in nearly the same temperature and sunlight, and we can keep out most bugs and animals that might interfere with our results.
In the field
We run some experiments in the field because the conditions in the field are more like what the plants would experience in real life. In the field it is more difficult to control some variables, sometimes it takes a lot of hard work, like putting a barrier in the ground to keep pests out.
In the lab
In the lab we make experimental observations. We measure mass of the leaves and roots, measure the concentration of nutrients in the plants, and we run tests that detect the presence of the virus by detecting its RNA or proteins.