T.S.
I found that if I kept having him try foods he has previously disliked he sometimes likes them. For instance as a baby he disliked anything green, but at a 4 year old his favorite veggies are broccoli, asparagus, green beans, and peas. I get him to try new food by involving him in the selection and preparation which your son may be a bit young for. What we do is that as we walk through the grocery store we talk about all the different fruits and veggies and which ones look really weird and if we should try them. Just the other day he pointed at something I had never tried, celery root and asked what it was and how it tasted. I told him what it was but that I had never tasted it and asked him if we should try it. He thought we should so we did. When we got home we looked online for recipes and he helped me choose one that sounded interesting and we made it. While it wasn't a big hit, it was a food adventure for us. He helps me prepare food by washing the veggies and other easy tasks such as breaking off the tough ends of asparagus. We have done this since he was about 3 and it has been lots of fun for all of us.
Good luck!