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Canker: Localized necrosis of the bark and cambium on stems, branches or twigs. They are often sunken because the stem continues to get bigger elsewhere. Also, callus may be produced around the canker that makes it more sunken.
Pathogens are mostly Ascomycota. Many also have an asexual stage in the Deuteromycota.
There are some diseases usually considered with other groups that also involve cankers:
Often, cankers are centered around a wound or branch stub, suggesting that they were the infection court. But seeing a branch at the center does not tell us much. Did the pathogen colonize the branch or stub after it was dead, then attack the nearby living stem? Or did it infect the branch while it was alive (perhaps through some kind of wound?) and then grow down into the stem, killing the branch in the process?
Some people have trouble with this. Cankers are a good topic for examples. For example, the pathogen of coral-spot Nectria canker has both a sexual and asexual fruiting structure that occur separately. The sexual structure is in the perithecial ascomycetes, characteristic of the genus Nectria, and the fungus is called Nectria cinnabarina.
The asexual structure is a sporodochium. Fungi with sporodochia are classified in the Deuteromycota. This particular sporodochium and conidia it produces belong in the genus Tubercularia, and this one is Tubercularia vulgaris.
So the pathogen has two names. They both refer to the same fungus. If we want to refer to the whole fungus (as we usually do), it is usually best to refer to the name for the sexual stage, because, as with plants, that is the stage usually used to indicate relationships. So we call this pathogen Nectria cinnabarina. But you may also hear people refer to the asexual stage by name.
For some fungi, though, we may just see the asexual stage. Cytospora canker is an example. We almost always only see pycnidia. So it is natural to call it by the stage that we see, Cytospora or Leucocytospora.
For some fungi, a sexual stage may never have been seen. Pitch canker is an example. All we see are sporodochia, so we can use only the name for the asexual stage, which in this case is Fusarium.
In other cases, there may be both stages, but the sexual stage is so consistently present that we don't need to use the name for the other stage and there may not be one. Hypoxylon canker is an example. There are conidia, but you never hear a name for that stage. There are almost always perithecia around to identify.