I let a volunteer tomato plant do its thing in my garden this year and it set fruit that look like Roma tomatoes. Very large Roma tomatoes. I didn't fertilize it at all, just watered it a few times. I didn't stake it up either, just letting it vine on the ground.
The plants I grew from commercial Roma VF seeds grew well but produce loads of very small fruits, no big ones. I fertilized these a couple times with chicken compost and staked them up off of the ground.
I don't know if the volunteer plant produced better fruit because of the soil it grew in or if it was the result of cross pollination. Whatever the reason I'll be saving seeds from the volunteer plant for next year's garden.
Roma VF on left - Volunteer tomato on the right.
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