paph leaf thingy.

[Stone]

I have noticed some extremely small pits on some seedlings which were sent to me and also on some others I've had for a while.
Nothing serious but does anyone have any idea what causes them? There is no color change and you can only really see them at certain light angles. Only one or two on the odd leaf. like a very small pin prick.

 

[Ozpaph]

A picture is worth a thousand words, if you can.

 

[Stone]

How did I know that would be the first reply?:rollhappy:
I'll try to get a picture on soon.

 

[eggshells]

mesophyll cell collapse perhaps.

 

[Ray]

mesophyll cell collapse perhaps.

That thought jumped into my mind for a second too, but as mesophyll collapse is caused by localized exposure to extreme cold, wouldn't it normally manifest itself as patches, rather than scattered spots?

Assuming I'm conjuring up the same image, I've seen those little pits Stone is referring to, never have figured out what they're from, and they don't seem to spread, suggesting some sort of mechanical damage.

 

[Ozpaph]

How did I know that would be the first reply?:rollhappy:
I'll try to get a picture on soon.

At least you answered one of your own questions - just not the important one!oke:

 

[Stone]

Ok here are a couple of pics. difficult to focus on.
This is a young phillipinesis. Has not been subjected to cold at any time.
New leaf grown over summer.



A helenae seedling which came to me like this. Don't know if its the same problem?



A young praestens.



It's more noticable on green leaf species but I've also seen it on mottled. So what do you think?

Mike.

 

[emydura]

I thought low humidity might have caused that.

 

[Stone]

I don't know David, My humidity averages around 60%?

 

[Ozpaph]

mesophyll collapse

 

[Stone]

Maybe the second and third? but if cold water/temps cause mesophyll collapse, not the first

 

[Ozpaph]

While I'd thought that's what mesophyll collapse looks like the web images look much more dramatic with large patches of dead cells, not like yours.
http://www.aos.org/Default.aspx?id=130
http://www.orchidboard.com/community/hybrids/17549-mesophyll-cell-collapse.html
http://prezi.com/bq6pnhi2lqyc/mesophyll-cell/
http://www.rv-orchidworks.com/orchidtalk/orchid-ailments-compost-pile/2611-paph-cell-collapse.html

 

[Stone]

That's what I thought too Ozpaph. I'm sure I've seen some MC on some of my Agaves with fleshy leaves and was probably caused by cold water from the hose. I think this is a different problem but it must be fairly wide-spread because I've seen it in paph seedlings sent from Qld, WA, NSW, and some of my own. I'm looking at Cu deficiency or interference of Cu by excess Fe at the moment but who the hell knows. Trace element problems in orchids just don't show up as definately as in woody plants.
If I can ask others to have a close look at their seedlings maybe we can come to some conclusion by the process of elimination

 

[Rick]

I used to see this pretty frequently in the older leaves of seedlings. And more commonly on newly aquired plants. I used to associate it with low humidity since I saw it a lot less when I forced humidity to stay > 70%.

However with Low K I'm seeing new growth with slick shiny new leaves. Keeping in mind that excess K can cause deficiency of almost any other element. I don't know if I'd chase after problems with the micro nutrients.

 

[Stone]

I used to see this pretty frequently in the older leaves of seedlings. And more commonly on newly aquired plants. I used to associate it with low humidity since I saw it a lot less when I forced humidity to stay > 70%.

However with Low K I'm seeing new growth with slick shiny new leaves. Keeping in mind that excess K can cause deficiency of almost any other element. I don't know if I'd chase after problems with the micro nutrients.

I've done a google on this and what I'm seeing is lots of questions and many foggy answers. Lots of people seem to have this problem but no one has a definative answer. One of the problems is confusion with similar looking disorders.
So far we've got : too much light, too dry between waterings, mite damage, micro fungus damage, low K, high K, cold water damage and others I forget:evil: Mite damage may be worth a look? The reason I say this is because after a real thourough second look, I discovered one of my vietnamense seedlings with one leaf totally covered with pits and the next totally clean. So it looks unlikely that it was temp or nutrient or light related but maybe it was cleaned up after a pesticide spray at the nursery? I think I will contact the vendor.

 

[Justin]

maybe i'm just a bad grower, but looks pretty normal to me.

 

[NYEric]

maybe i'm just a bad grower, but looks pretty normal to me.

ity:

 

[Rick]

Yes I think its a pretty common problem so I'm not even sure if it is a problem.

Total perfection!!

 

[emydura]

I notice it shortly after I take seedlings out of a flask and with some of the Barbata species, which always made me think it was a humidity issue. It always seems to go away so I have never worrid about it.

 

[Stone]

SOLVED!!!!, At least I think so. It's mites. I took my little 10x lens into the g/h this morning and had a really close look at all the seedlings and some adults and found (on what looked like perfectly clean, healthy glossy leaves), 3 species of mite!! One was light brown almost translucent, one big fat and glossy brown and the other red and fuzzy. I suspect that one or more may be predetory mites but where there's predetors......
Most plants were clean but they seem to be quite mobile (not the webbing kind) so they possibly feed at night and hide in the p/mix by day?
I also suspect they also may contribute to the occasional outbreak of bacterial infection.
My feeling is that the damage is caused when the leaf is very young and still actively growing, the mites come along and pierce the cuticle and as the leaf expands, it forms a pit around the dead puncture site?
I think if I had a 20x or 50x lens I may find even more things.