Kinda ironic that folks are catching onto the idea of doing more breeding work. I used to specialize in heat tolerance with thousands of crosses tested in hot spots of California. I would start in the Indio, CA. area near the Salton Sea or the Los Angeles area and work north to Bakersfield, Buttonwillow, Fresno area and way up above Sacramento in the central valley.
With many years of doing just that and with hundreds of crosses, sometimes different collections, but always with a heat tolerant aspect. I developed inbreds from many of the hybrids and tested lines from other programs. I did find some lines to be excellent for production, color, and firmness. Sometimes for flavor, but many times just to be acceptable but nothing to brag about.
Heat tolerant lines out of Fla. might be the best if you are living there with the humidity, which is different from the dry heat of California. The one inbred that I have used for heat tolerance for the last 14 years is so poor in flavor that I use it for comparison taste samplings. I could do a show on "What tomato not to eat" that would make "What not to Wear" seem tame.
I live in the PNW where heat tolerance would be oxymoronic; what a tomato that can tolerant 59 F for a high in middle of June?
I already have hybrids (seed is still OK), so why would someone want to start a "Southern" line of tomatoes from scratch? To each his own makes sense.
I was just on the phone with Dr. Carol Deppe who is the author of
Breed Your Own Vegetable Varieties
and we were talking how plant breeders rarely make any money on their varieties. She wants me to write a book soon with her publisher.
Back to breeding your own tomatoes, go for it. Funny that one of my own varieties, Green Zebra, was mentioned as a heat tolerant variety! Bred up in Kansas by a farm boy that was looking for something to take the heat, take the drought, take the 19 inches of rain in July, take the hail, take the tornadoes, take the wind, take the grasshoppers, and even takes the cake!
Just think, "Man made tomato for Man made Global Warming!" I am waiting for that ocean side property in Arizona! I'd better get the humidity tolerance bred into the Green Zebra fast. Oh, wait a minute; been there, done that. But not that the Global Warming Alarmists would ever care!