You may be able to distinguish heirloom tomatoes from hybrids by looking closely at their fruit. Heirlooms come in various colors, including fruits tinged with black, purple and pink, as well as bright yellow and orange pear shapes. They often have softer skins that can crack, and an odd, less symmetric look. But the real difference isn't so evident on the surface. Heirloom tomatoes and hybrid tomatoes are essentially opposites on the genetic level.
Hybrid plants result from controlled pollination of carefully chosen parent plants, notes the University of Illinois Extension. Hybrid seeds are called F1 and possess characteristics that present a combination of both parents. Heirloom tomatoes are open pollinated, meaning that wind and insects carry pollen from one plant to another and the offspring will be true to each parent.
You can save seeds of favorite heirloom tomatoes from year to year. Seeds saved from hybrid tomato fruits, which lead to F2 plants, perform unpredictably, as the traits from the F2's grandparent plants appear in widely varying ways. Consistent F1 hybrids arise only by repeating the original cross each season. While heirloom tomato offspring behave fairly predictably, their traits may vary with a fixed range, notes the University of Tennessee Institute of Agriculture. For example, Brandywine seed selected yearly from the best-tasting fruit in hot, humid Tennessee may vary from Brandywines selected in hot, dry Northern California.
Heirloom or open-pollinated plants provide a larger gene pool for future breeding, notes the University of Illinois Extension. Heirlooms win plaudits for their superior flavor, color and texture. Hybrid tomatoes may be stronger at surviving challenging environments, such as humid growing areas where wilt diseases pose a problem, as well as keeping better for commercial shipping and maturing earlier.
Well-known heirloom tomatoes include Brandywine, originating in Chester County, Pennsylvania, in 1885. Other heirloom cultivars include Cherokee Purple, Georgia Streak, Yellow Pear, Arkansas Traveler, Mortgage Lifter, Druzba, some lines of Rutgers, Stupice and Eva's Purple Ball. Hybrids include Early Girl, Better Boy, Big Beef, Jet Star, Park's Whopper, Supersonic, Beefsteak and Celebrity.
The oldest heirloom tomatoes date back a century or more to the beginning of the tomato craze in the United States; other heirlooms date to pre-World War II, with many bought to the United States by Russian and Czech immigrants. Hybrid tomatoes date from seed grower David Burpee's trials in the 1930s that led to the stupendously popular Big Boy tomato.