first try

Nothing to worry about. If any it's beneficial.

sono micorizze sono utilissime per l'assorbimento di nutrimenti...

spritz it with soem h2o2.. 3% is fine fo a superficial application. i wouldn't dilute it for this function. it will kill more effectively. Luckily, most fungus growing on surface is not much of a concern, though more so for a young plant. This stuff typically is feeding off of decaying matter in substrate, not the roots. So, adjust use some H2O2 3% and spray it down. and reflect on watering habits.. if top layer is always wet, you are watering too frequently and this is very likely the cause of the problem. Secondly, i see no perlite or similar.. so your drainage qualities are lacking.. which also contributes to this problem as well as other negatives for your root zone.