Good post Bob. Thanks for straighting the UK boys out.

Dave

Hi Dave,

It's not my intention to target anyone or any group. I have many friends in the UK and on the continent as well as in the States. I just chime in once in a while when I see misinformation thrown out into a public forum and no one refutes it for a few days. There is enough misinformation on the internet. My students come across it all of the time when they use the world wide web as a source of information for assigned projects.

Bob

With respect to "Point #1: Witches' brooms that develop from pathogens do not propagate"

Can we really know that for sure? Just becuase the witches broom trait is heritable doesn't necessarily mean it wasn't caused by a pathogen. The pathogen could cause a genetic mututation. Some human cancers (cancers are afterall genetic mutations) for example are caused by viruses like HPV. That's the reason for the push for HPV vaccines - If you don't get the virus your less likely to get certain cancers. I'm not saying you're wrong. Just speculating. If there is any published literature on this I would appreciate the citation so I could read it. Again, not saying your wrong - just interested.

Bob I retract that comment and apologize.

Thanks for making a one sided post not so one sided. Now we can put this to bed.

As for me I am going to move on and keep on learning from those that provide good information. This will be my last post on the GW.

I am out of here.

Dave

Dave

Hi Bob,

Thanks for the post!

I have to agree with Useyourloaf, though - how certain is that about brooms? As far as I'm aware, most brooms have never been tested for their cause. As well as viruses, there's a whole new class of plant pathogens called Phytoplasmas, which have been isolated so recently that none of them have even been scientifically named yet (they are all known by informal provisional names); some of them are associated with transmissible (spread by sapsucking insects) broom-like diseases of flowering plants; several are of major economic concern (e.g. coconut lethal yellowing), and none is treatable. How many conifer brooms have been tested for them?

Resin

PS Dave - I know we've had differences (most people do, sooner or later!), but don't feel obliged to leave! You've plenty to contribute here. Hope you'll stay!

The general consensus seems to be that when a broom is induced by a pathogen, it will not be a single, isolated broom. There will be an assortment of them upon the tree.

The following information is on my web site and based upon some of my research done a number of years ago.

There are several ideas which attempt to explain the origin of a witches' broom. Most brooms are thought to be viral in origin. A virus upsets the hormonal balance in an elongating bud, causing it to grow little but produce many lateral branches. Such growth continues until the broom chokes itself or is shaded to death, provided the hormonal irregularities themselves are not fatal. If this type of broom is propagated, the progeny will fail immediately, or within just a few years. One clue that a discovered broom is of this type would be the observation of several brooms within a small area, indicating that the virus spread through the area like a disease.

Brooms that do propagate successfully are attributed to other causes. These 'other causes' have never really been defined. But some interesting facts or clues are known. Cytokinens are found at a higher than normal level in a witches'-broom. Cytokinens are hormones that do not move very freely around the plant. Their presence stimulates cell divisions. The hormone, giberillen, which encourages shoot elongation is present at reduced levels, especially in a virally produced broom.

How these unknown agents upset the hormonal balances in a bud and how they are able to persist into the resulting brooms are questions that still need explanation. Since these agents apparently have a genetic influence as well, the questions are even more complex than they first appear. Grafting a small piece of a 'nonviral' witches' broom onto a seedling will generally create a plant with the characteristics of the original broom. The hormonal imbalance apparently remains, even though a new stem and root system have been added. (Of course the broom itself was on a species-normal trunk and root system while attached to the parent tree.) Either a causative agent was in the piece of broom that was grafted or the genetic structure of the cells was imprinted with a new hormonal code equal to that of the whole broom.

Almost all witches' brooms that have been observed to flower have been female. (Pinus sylvestris 'Longmore' is a male broom). If the egg cells are fertilized, the resulting seeds produce a high percentage of dwarf plants. Those dwarfs result from the normal sperm cell from the male flowers of the tree fertilizing the eggs of the abnormal witches' broom. Either the eggs have an altered genetic structure or the causative agent is somehow encapsulated within the seed. The variation of growth rates exhibited by the seedlings, however, indicates genetic changes. A causative agent would be expected to product a relatively uniform population of species normal and witches' broom duplicates, with little or nothing in between.

Some seedlings from witches' brooms will die at a young age, develop into weak, sickly plants, or consistently exhibit dead areas. Other seedlings from the same source will be normal in all observable ways while others will develop into compact or dense plants and a few will become quite dwarf. Such variation within a population is thought to be due to genetic factors.

Since there has never been a documented case of a witches' broom bringing any sort of a disease into a "clean" population of the same species in a garden setting, I believe that any causative agent is long gone and is most likely some form of radiation.

Bob

By the way- stick around Dave, I enjoy your enthusiasm and we all get carried away at times. Life is too short for anyone to foster any hard feelings over statements that are made on the spur of the moment and come across in a way not intended.

Interesting discussion.
My question is whether there are any sort of (semi-) reliable statistics on the abundance of WBs around the world.
From some of the posts from wbgarden.com, one gets the impression that central Europe is particularly well endowed in WBs.
In the last century, an area known as the 'Black Triangle' -- comprising East Germany, Czech Republic and Poland -- was recognized for being the most industrially polluted in Europe.
I recall that pollution from my youth: on some winter days, the snow was so covered with soot, that you could write white-on-black text in it.

What I'm getting at is that WBs are probably more likely caused by chemicals than, as Bob says above, by radiation.
Radiation is a very poor mutagen, compared to many chemical toxins.

Conditions in the 'Black Triangle' have improved greatly over the last few decades, as some old coal power plants (and mines) have been shut down, and remaining ones have improved pollution mitigation.
In addition, power from the shut coal plants in the Czech Republic has been replaced by nuclear reactors (four at Dukovany and two at Temelin).
Poland is now planning to do likewise.

So the great central European WB 'bonanza' may be coming to an end, in a few more decades.

Pollution may have an influence but that wouldn't explain the thousands of brooms found by Jerry Morris all through the Sierra Nevada and Rocky Mountain ranges, which are relatively pristine environments. Jerry has made some interesting observations and relates their origins to radiation effects.

Bob

Thanks Bob,
Could it be a matter of WB concentration ? ....the Sierra Nevada and Rocky Mountain ranges are probably something like ten times the area of the 'Black Triangle' (or at least the forested parts of the latter).

Also, what is the concentration of WBs in the Sierra Nevada and Rocky Mountain ranges, compared to other similarly forested areas of the USA ?

Is the number of WBs found by Jerry simply due to the fact that those mountain ranges have more forest area to search through ?
(BTW, has Jerry published anything on this topic, that we could read ? ....a reference would be greatly appreciated)

Lastly, if the implication is that increased radiation due to mountain altitude is the relation linking WB abundance, then it is a weak link, because even at high altitude, radiation dose rates are not very high -- only about three times those at sea level.
Moreover, there is plenty of evidence that these elevated dose rates are still well below those levels where biological defense mechanisms are overwhelmed, causing deleterious effects, instead of the beneficial defense-stimulating ("hormetic") effects actually observed (ie. reduced incidence of cancers, etc. in high-altitude states, compared to low-altitude ones...).

Although high altitude habitats well away from cities are less polluted there is some stuff that has gotten everywhere, even the polar icecaps have pollutants in them now. And the deterioration of the atmosphere could be letting in solar radiation that affects some conifers, those on the tops of mountains get lots of sun exposure and may perhaps also be species especially sensitive or responsive to deterioration or alteration of environmental conditions.

Jaro - you're pretty smart.

Thanks for the discussion and I'll enjoy reading any further continuation on this topic as well.

(Bob if you've posted in your opinion enough, I appreciate all the information you added).

Dax

What an excellent discussion. Thanks to all.

tj

Worth adding to Bboy's comments, that pollution (particularly by volatile pollutants) is a lot worse at high altitudes and in polar regions, because the colder temperatures there increase both its deposition rate and retention period in the environment.

Resin