Have you tried using small pieces of high value treats such as cheese or frankfurter? I know that they're not low in calories, but in small pieces they might still help with the training. I've always found that Henry's interest is much better if the treat is a good one (even if it's tiny) - the smell and taste of a tiny piece of frankfurter is way more important to him than a larger liver-flavoured training treat, for example.
I moved Henry on to adult food at 7 months, as he was castrated. I think puppy food could be too rich for a 9-month-old dog.