We have been growing tomatoes for years and over the last few years have had trouble with them dying off after planting from the bottom up. It seems to be a bug that crawls into the stem. Leaves die off at the bottom at the beginning then further up as the season progresses. Plant eventually dies.
This could be insect or a fungus issue. If you are having this same issue and are planting in the same location you may have a soil issue.
Crop rotation is recommended to help avoid these issues.
I'm listing a few articles that may help you pinpoint the issues and help you have better results in your next growing season.