if the site will be an open forum where people can write about their love for tomatoes. I think domain name is not a problem and why you need seo? just create good looking name Tomatoist is good name. for example "digitalpoint" there is no relation with seo and the content I think. tell me if i'm wrong.
All good points provided here. But yeah, you can't really brand "I love tomato's". The highens are hard for people to remember and type and they just plain look bad. Not many people are going to search I love tomato's anyways. You can still use that phraze though if you wanted. Just put it in the title of the site. The titles are important.