The organism among the given options which is the most harmful to the tree that it grows on is the strangler fig. The strangler fig is a type of the tropical fig. It grows on host trees, which leads to the death of the host. The roots of the strangler fig moves over the trunk of the host tree covering it. The multiple roots graft together and enclose the host completely.
Hence, the correct answer is 'option A - strangler fig'.
