HYBRIDIZATION TEST

We can use antibodies to detect viruses because each virus has a unique protein coat that an antibody will stick to. But one group of pathogens, collectively called viroids, have no protein at all just a circular piece of the nucleic acid RNA. To detect viroids, we use a hybridization test, which can find this RNA. RNA "hybridizes" when two single strands come together like a zipper to form a double strand. To detect viroid RNA, we use a labeled piece of RNA called a probe that can hybridize with RNA from the sample.

First we extract the RNA from plant samples. Then we attach the RNA to a membrane. We apply the RNA probe, which is labeled with a chemical called DIG. If a viroid is present, the probe hybridizes with it. If not, the probe is lost when we wash the membrane.

To see the result of the test, we treat the membrane with a process that gives off light if DIG is present. We expose film to the membrane to detect the light. A spot on the film means that the viroid is present. Along with your samples, we also test samples from healthy and infected plants as controls.