Willeke,
I sent a note to you stating that I thought you should check it out and treat with sulfur dust.
I am of the thought that it would be worth sending off a quick note to Sundaram and ask him. He may have treated it himself with something. He will answer you and if he has not, then he will probably give you similar advise as I.
When I get trees with dark spots on them. I usually scrape it off so that I can see if it is only on the surface. If it is more and needs to be cut off a bit more. Then dust with sulfur dust and hang it with a soft rope in a dry and warm site for a week or two. Not in Sunlight.
I have read that many in Thailand and India use Turmeric powder to treat. Need to do some checking and ask them why and how it works.
Do not worry about this tree, Willeke. It will be fine. I always like to check these things before burying them in soil and not knowing what I am dealing with prior.
Rick