As reported by Flock and Wallace in 1957, eriophyid mites can transfer mosaic disease in less than 10 days.

http://californiaagriculture.ucanr.org/landingpage.cfm?articleid=ca.v011n01p12

Mites are impossible to see, for me anyway, without magnification. So, they are easy to miss. It is entirely possible that you have fig mites in your growing area and the mosaic disease was transferred from one or more of your infected plants. If you want seedlings to stay mottling disease free, they need to be grown in a restricted area or clean greenhouse environment from what I read in the scientific literature.

Because FMV is an RNA virus and RNA viruses normally have error-prone polymerases, there are lots of minor variants of FMV. There is not much published on the degree of variation as yet or how the variants might impact mottling disease. Just to make things yet more complex, at least 8 additional fig viruses that cause mottling have been identified in the past few years causing the disease to be referred to by the scientists as fig mosaic (or mottling) disease, FMD for short. They are:

Fig Leaf Mottle-Associated Virsus 1 & 2  (FLMaV 1 & 2)

Fig Mild Mottle-Associated Virus  (FMMaV)

Fig Latent Virus 1  (FLV-1)

Arkansas Fig Closterovirus 1 & 2  (AFCV 1 & 2)

Fig Badnavirus-1  (FBaV 1)

Fig Cryptic Virus  (FCV)

Several of the above viruses are also RNA viruses with meaningful variation between different isolates just to make the puzzle more annoying.

The Falk lab at UC Davis and the Martelli lab in Italy were the 2 groups to isolate and get the genetic sequence of FMV.

http://apsjournals.apsnet.org/doi/pdf/10.1094/PDIS-93-1-0004

http://vir.sgmjournals.org/content/90/5/1281.full.pdf+html

It appears that FMV is not transmitted in seedlings. However, FLV-1 is reported to be transmitted in seedlings. I do not know about the other viruses.

http://sipav.org/main/jpp/index.php/jpp/article/view/563

Reports are starting to appear of efforts to screen trees across broad areas for FMV and other viruses. The ones that I have seen find FMV broadly distributed. They are using PCR based methods to detect. My guess is they are getting some false negatives even when >90% rates of infection are found. I hope this is useful.

Good luck with your trees!!

I hope I can clarify a couple of points here. As I mentioned above, according to the literature labs grow seedlings in glasshouses (the term used for greenhouse) or pots under a screen system to get FMV free trees. There are many scientific papers starting with one published with Condit in 1933 demonstrating that FMD/FMV is NOT seed transmissible. Any of you interested in learning more about seed transmission of plant viruses may find this review helpful.

http://www.dias.kvl.dk/EJCVetc/Johansenetal1994.pdf

Gina, thank you for the Wikipedia link! I read a recent paper that I neglected to grab as a pdf and now can not find saying current thinking is ~30% of plant viruses can be seed transmitted. The upward revision comes with the finding that some viruses seed transmit inefficiently causing some to be missed initially. In the case of fig viruses, FLV-1 is the only one to date demonstrated to be seed transmitted. FLV-1 is reported to cause a mild mottling condition at worst and is apparently not the cause of significant FMD by itself. Many trees are infected by multiple viruses. The degree to which FLV-1 might interact with other viruses and cause significant FMD is unknown.

http://www.sipav.org/main/jpp/index.php/jpp/article/viewFile/546/334

Herman, as usual, I think cuts right to the core of the problem and supplies us a big dose of common sense. It seems to me he has constructed a pretty effective solution for himself by vigorously working to only retain the healthiest trees in his collection. Although, I have a fair bit of experience with citrus, apricots & plums, I have only been playing with figs for 18 months. So, I pay close attention to Herman's experience(s) as he posts. My reading of the literature is that the scientists actively studying FMD believe that FMV is the usual cause of significant FMD as opposed to mild mottling. The degree to which the different variants of FMV cause greater or lessor disease is unknown. The degree to which the other fig mottling viruses I list in my post above cause significant FMD alone or in conjunction with any of the other viruses is unknown. The degree to which HOW you grow your fig trees might affect whether they show FMD is unknown although anecdotes like luke's above surely suggest there is something there. I think it is clear that it is a complex problem & there is a lot yet to be discovered. So, there is a lot to be said for Herman's common sense, practical approach.

Relative to whether these fig viruses are intracellular (inside the cell)  or intercellular (outside the cell), the statement that bacteria and viruses need not be intracellular is correct. However, for a virus to replicate and cause pathology, it must be intracellular. Bacteria and fungi do not normally need host cell machinery to reproduce and can exist either intracellularly or intercellularly and cause disease either way depending on the particular microorganism.

There is one intriguing possibility that might supply a possible treatment for FMD. Aspirin. Salicylic acid (aspirin) is produced by plants in response to infection by pathogens and activates the plant's innate immune system. It has been demonstrated that treatment with salicylic acid can prevent or limit several plant infectious diseases.

http://segenetica.es/cng2/cng2008/biblio/Ref-Marc-Valls---Jones-and-Dangl-Nat06.pdf

http://igitur-archive.library.uu.nl/bio/2009-0512-200821/NatChemBiol-Pieterse-2009.pdf

This is my first year propagating from cuttings. All but one of my cuttings are from Encanto (thanks Jon!!!). Two of my 3 Sicilian Black Italian cuttings are doing well and showing little, if any, sign of FMD. However, one started showing significant FMD several weeks ago. It had been doing well but slowed up as the FMD appeared. I do a foliar spray of worm casting tea that contains salicylic acid on my tomatoes roughly every week. So, I decided to spray the fig too. After 2 sprayings, the leaves have greened considerably and the mottling is clearly decreased. How much of that is due to the aspirin or nutrition from the worm casting tea or both I can not say. My plan is to try to test for any aspirin effect more carefully next year on what I think many (most?) would agree is a true FMD challenge: cuttings from UC Davis. I will propagate some with and some without routine salicylic acid treatment and see if there is an impact on FMD appearance. I am assuming that they provide several cuttings of each cultivar as Jon did. If not, I'll have to try something else.

Good luck with your trees!