Hi,
As the help page of AntConc explains, "The format of the headword//lemma/grouping list is as follows (where -> represents a tab character)"
So, just replace your -> character with a tab and everything should work.
Saying that, I usually recommend that people POS tag their entire corpus, for example with my TagAnt tool, and then load that data into AntConc via the corpus manager, using the simple_word_pos_headword indexer. Then, you'll have lemma and POS information that you can use. It's much more reliable.
Regards,
Laurence.