I second the question: Is this about manners or food?
We expect our children to sit at meals with us, try everything that is prepared, and sit with us until we are finished. Manners are important! Food is a whole other ball of wax. We encourage everyone to try everything that is prepared, although if the child doesn't like it, they are not forced to continue eating the food (I don't like eating something that I find distasteful, and I'm sure my children don't either). We feel that 1) learning to try new foods is part of expanding one's palate, and 2) it's good manners to try things, as there will inevitably be something at a hostess's house that you've never encountered before. Again, if the food is not a hit, the child does not have to finish it. Who cares? Why make it a battle? They've all grown up with these expectations, so it's not hard for them to follow them.
WRT to sitting at the meal, we find that there is a lot of up-and-down for several years until they gain the maturity to sit peacefully through a meal. Sometimes we feel like we are eating with a bunch of popcorn, lol, but we just keep reminding them to sit down and eat. We start when they are babies, sitting on my or DH's lap, playing with a spoon. Again, since our children have grown up with the expectation that they will sit with us through the meal, they don't get upset when we remind them to stay in their seat; it doesn't feel repressive to them like it might if we waited until age 3 or 4, kwim? It's just the way it is.
As far as enforcing our "rules", we don't have any punishments or whatever for not "obeying". We rely more on modeling good manners: staying in your seat through the meal, chewing with your mouth closed, not talking with your mouth full, etc. We also make sure that our children know what we expect them to do; how can you expect them to know what you want unless you spend time teaching them?
As our children get older, we are finding that it's a lot of fun to share meals with them when we come to the table with something to talk about. Sometimes it's jokes we share, word problems (like riddles or something similar), interesting things we've learned, the highlights of our day, etc. Sitting together enjoying good food makes all the work of teaching manners totally worthwhile!
I would just say forget the food battles. Like SundayCrepes said, they will eventually try and like most things, so why make a big fuss over cleaning plates and whatnot. If you want them to try things, like we do, make it a part of your life, and be excited yourself when there is something new to try. Make new recipes and treat it like an adventure (we say "we might love it and think it's the best thing ever, we might hate it, throw it out, and eat PB&J for supper, you never know!"). They will catch your excitement, and be more willing to experiment as well.