How do we know if a tree has a hypovirulent infection?

Step 1: Collect a bark sample from the growing edge of the infection. Make sure the sample is deep enough to capture the fungus, which is under the bark in the living layer of the tree-the cambium. You can use a cork borer or a biopsy tool to punch a neat, circular hole through the bark. Minimize contamination by sterilizing your tools. You can dip them in alcohol and flame them to burn off any other fungi.

Step 2: Take a dozen samples around the edge of the canker and put them each in an individual well in a microtiter dish. Cover the tray with a nickel-plated screen. Use rubber bands to hold the screen on the tray. Put it in an old ice cube tray or in a bread pan and fill the tray with a solution of 1 part household bleach to 9 parts deionized water, with a squirt of soap. Let it soak for 14 minutes.

Step 3: Put the bark sample in a petri dish. The petri dish will contain a potato dextrose agar with antibiotics to keep bacterial infection at bay. Grow it for one week at 20 degrees Celsius with a 16-8 photoperiod (16 hours of light, 8 hours of dark). These are prime conditions for fungal growth and you should end up with a culture like the one below. The appearance of the fungus is a clue to whether it has hypovirus or not. But the only real way to know whether it is infected or not is to search for dsRNA, or double stranded RNA. dsRNA does not exist outside of the virus.