>>Peter wrote: 5. A strong parasite on a susceptible species is not compartmentalized at all, but only slowed in its colonizing activities by defensive reactions including hypersensitive reaction and production of phytoalexins.

I think we need a definition of compartmentalization. Does that mean fully confining the infection, or does it include a partial or temporary blockage of progress? If the former, then I will agree with your statement.

I think however, that even the susceptible trees react to the infection. Infection zones can be found in willow and aspen. The parasites have the potential to penetrate those barriers, seemingly. What do fungal parasites do? They produce solvents that break the chemical bonds between molecules within the cell wall components, then absorb some of the byproducts of the dissolution. They are simply chemical factories. The tree's response is to produce chemicals that are resistant to the solvents. In the case of the susceptible species, the fungus has produced solvents that are not resisted by the trees' response. Hence, they may be slowed but not stopped.

What are the other thoughts on this?

One step further, Peter. WE earlier had a discussion on whether the "walls" in CODIT were real or imaginary. This is part of my argument that they are real. The tree does not form any new physical feature that wasn't there before, and looking with a microscope will reveal the same structure. But the molecular changes are real, and in some cases quite measureable. Sort of like painting the wall in your office- The wall is the same dimensions (given a slight thickness for the paint) but it otherwise looks the same.

Reply to post by Russ Carlson, on February 19, 1999 at 00:29:31:

I am a newcomer to this discussion, but here are my two-cents.
Compartmentalization is a process in response to injury and infection. This process (that consists of lots of different activities!) tends to resist the spread of infection. The goal of compartmentalization is tree survival, which generally means keeping the infection away from the vascular cambium. Trees don't care if they are hollow. Hollow trees indicate successful compartmentalization. Some diseases, such as sapstreak disease of maples, spread quickly and do an "end run" around the boundaries formed by the tree to resist its spread. Other diseases such as canker rots jump back and forth between the bark and the wood, killing the cambium and avoiding the compartmentalization boundaries. Some pathogens such as Armillaria can, under certain conditions, burn through compartmentalization boundaries. In all of these cases, I would contend that compartmentalization, as a process, did occur. It was just less rather than more successful. We need to think of compartmentalization as a moving set of boundaries, not as a static on-or-off condition. CODIT is another matter. CODIT was a model published in the 1970's to describe compartmentalization. Actually, for a 20-year-old model, it does pretty well although it has its shortcomings. I do research on compartmentalization but almost never, except in a historical context, refer to CODIT or "walls". There are boundaries that repeatedly are set and breached and are sometimes more effective than other times.
Perhaps this will provoke more discussion.
Kevin.

Reply to post by Russ Carlson, on February 19, 1999 at 00:29:31:

To me, compartmentalization means fully confining the infection. If the infection breaches the wall, the temporary barrier that slowed the infection down is dissolved.
The hypersensitive reaction, in which cells self-destruct, isolates a parasite that needs living cells to live, and therefore confines it. If the fungus forms resting spores, which are dormant, and by an injury (drill bit? - see, I'm not totally closed-minded) is introduced into live cells, it might be re-activated.
If it is just a matter of slowing down infection by introducing caustic chemicals- phytoalexins- into the battle zone, I would not call it compartmentalization. I agree that introducing phytoalexins into wood fibers constitutes a codit wall. The chemicals are real, but the wall is an interpretation. Unreal. Figure of speech. Perfectly valid.

Reply to post by Kevin T Smith, on February 19, 1999 at 00:29:31:

Kevin, you wrote, "There are boundaries that repeatedly are set and breached and are sometimes more effective than other times".
I like the sound of you terms. Perhaps if I use "boundaries" rather than codit walls, I'll be able to simplify my thoughts and conversations. Please elaborate, if you have a little time. If you have a little time, maybe you could start a thread about boundaries rather than us keeping this one going on. Peter

Reply to post by Peter Torres, on February 19, 1999 at 00:29:31:

>>If it is just a matter of slowing down infection by introducing caustic chemicals- phytoalexins- into the battle zone, I would not call it compartmentalization. I agree that introducing phytoalexins into wood fibers constitutes a codit wall. The chemicals are real, but the wall is an interpretation. Unreal. Figure of speech. Perfectly valid.

We need a definition of "wall". [g]

Just because the barriers are not absolute in their containment does not mean they are not barriers. The walls may be only made of paper instead of glass or concrete, but they function as a barrier, if only to slow progression of infection. I don't see the use of the term 'wall' as an impedement to the understanding. It is an interpretation to call it a wall- something we are all familiar with- but the barrier formed is still real, be it physical or chemical. It is not necessarily absolute in either function or position. I won't say the barrier moves, but rather is continuously recreated as it retreats before the infection. But it does compartmentalize in the sense that it confines the infection and slows progress, providing more time for other tree responses to adapt and prolong the life of the individual.