Pioneer Pathogen - A pioneer pathogen is the first organism to interact with the tree or the reaction zone formed by the tree after wounding or the failure of a protection zone at a natural opening. The pioneer must first compete effectively with other organisms on the wound surface, and then be able to grow into the tree against the pressure of the tree defense system. Many organisms grow on the wound surface, but very few, relatively, are able to grow into the tree. The pioneer stimulates the tree to mount a protection boundary. But, the pioneer may also be able to digest the boundary. Trees have defense processes and so do the pathogens. The tree may form an antimicrobial substance, but the pathogen may alter, or tan the compound and render it safe, or even use it for food. The pioneer is "playing" a seesaw game with the tree. As the tree and the pathogen interact, space occupied by the pioneer may increase. Then the pioneer must "fight" on 2 fronts; one, to spread in the tree, and two, to keep other organisms out of its "captured" space. It is not easy to be a pathogen in a healthy tree. It is easy to be a pathogen in a weak tree.
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