Apple tree disease on a 3 years old tree

[Yorann]

 

I sowed an apple tree three years ago, and it has been thriving in a pot since then. We are now planning to transplant it into the garden. However, I've noticed that some of its leaves appear to have a fungal infection, especially at the growing tips where the leaves are starting to die. I'm uncertain whether this is solely due to a fungal infection or if it could be related to issues with the pot or watering. Can someone help me identify the problem?