Here's what I found in a translation of Sylvia S. Madder Biology textbook (the picture was grayscale):

Under the picture it says:
"Test results show that citrus trees with mycorrhiza (+MYCO) were growing much better, than without mycorrhiza (-MYCO). [Left plants - non fertilized, middle plants - fertilized with half strength solution, right plants - fully fertilized.] Upper left corner image shows roots of Pinus contorta with symbiotic fungus hypha."

What do you think? Have you ever heard about anything like this?

It's certainly true, and has been known to be true for many years. However, realize that ALL healthy citrus trees already have mycorrhizae. Otherwise, they'd not be healthy. It is believed that in Florida, it would not be possible for a tree to take up enough phosphorous, regardless of how much fertilizer you used, without them. They are ubiquitous. Their spores are in the air.

So the only places where a benefit of PURCHASED or APPLIED mycorrhizae is usually shown is in short-term crops (like vegetables) on recently fumigated soil, to bring the infection rate back up in a hurry. For long-term plants like citrus, even if you planted sterilized seeds in sterilized soil, as long as the plant was then grown in the open air, it would become reinfected within weeks.

This is very interesting. Indoors and in the greenhouse I have a problem with damping off killing seedlings. I try to take all the appropriate precautions but it still occurs. Would applying purchased mycorrhizae to the sterile soil help prevent damping off by providing too much competition for the bad fungii?

No. Just apply any of the several common fungicides sold at most every garden center for the control of damping off (Rhizoctonia - Pythium). Further with small seedllings, water only in the morning, and then set the container in the sun to quickly dry off the soil's surface. Damping off fungi require moisture. - Millet (709-)

We have some sort of "mycorrhiza vaccine" for orchids. What would happen to citrus when such product introduced to the substrate?
And why the plants fertilized at 1/2 strength appear to be a little bigger than full strength in the picture?

The study pic shows either +myco or -myco. It would be interesting to find out exactly what(if anything) was added for the +myco and/or what was eliminated for the -myco,(sterilized media ??) and how they prevented recolonisation of the -myco test pots by airborne mycos ?