A few months ago several newspapers printed the astonishing news that a group of plant geneticists has decoded the entire tomato genome and found that the lowly tomato has 31,760 genes—about 7,000 more than mere humans. The geneticists probably had some good reasons for decoding the tomato but there are already thousands of tomato varieties that taste pretty good.
Bear with us while we get a little technical. This genome is only for the species of our common tomato: Lycopersicon esculentum which is the origin of all our Heirloom varieties, but there are twenty-eight other species of tomatoes growing down in Peru and Chile. Two of those species have varieties with pretty good traits, which tomato breeders are using to produce hybrids with resistance to various diseases. (It is also how they are getting tomatoes that will ship well commercially because of the hard skins and pitiful taste.)
Now we want to introduce you to our new vegetable expert: Dr. Kiki Fontenot. Kiki is the bright, hard-working replacement for Jimmy Boudreaux, who has retired. Kiki and Charlie Johnson are cooperating on a project to graft heirloom tomatoes onto hybrid, disease resistant, rootstocks. This is a work in progress and is larger than what we are describing. Also, what we have seen during this first year of trials may, or may not, hold up over several years. We lawn-chair gardeners no longer write research papers. We prefer to offer interesting information and dreams for the future.
This practice of grafting onto good rootstocks is very old and common. The satsuma trees that do so well in Louisiana are grafted onto seedlings of a plant called trifoliata bitter orange. It is of a different genus and is barely in the same family but it goes pretty dormant during the winter. This makes our satsuma trees go dormant enough to resist all but the most severe winters. Several years ago Charlie worked on the very delicate process of grafting watermelon seedlings onto the seedlings of a gourd. This gourd produces a much larger root system than does the watermelon. It resulted in a rapidly growing watermelon vine that required very little fertilizer and produced large, sweet, melons.
So, Kiki and Charlie began a study with stem tips of seedling tomatoes grafted onto seedlings from the disease resistant hybrid tomatoes. This grafting is something that you could do at home but we won’t describe it—they will do that in the research paper that will come out in a few years. Back in late June the Burden Center had a garden show in which Kiki and Charlie showed the first-year results of the study and, in general, it looked pretty good. Most of the heirloom varieties on their own rootstocks were a near disaster because the hot and damp weather promoted the bacterial stem rot that is a frequent problem. Those on some resistant rootstocks held up very well. The plants weren’t quite as large but, for some reason, produced more tomatoes than would have been expected. Maybe we should add here that they planted a lot of heirloom tomatoes as seedlings, but only grafted a few onto rootstocks. They were working on the concept before trying it on many varieties.
People’s tastes in tomatoes vary, and far be it from us to say which is the best tomato, but there are a lot of heirloom tomatoes that are very popular except for disease and insect problems. After the test at Burden was completed, Leon was allowed to pick and sample among the remaining fruit of Heirloom plants. The old Mortgage Lifter variety that Leon liked hadn’t fared well with disease but the fruit was good and very large. They had two varieties that we hadn’t seen before: Hillbilly and Persimmon. The Persimmon is a large yellow fruit that is juicy with a creamy taste but it is irregular in shape and doesn’t cut into slices that can be made into a sandwich. The Hillbilly is large, ugly, and has a lot of cracks but with a good flavor. Kiki made a good selection of heirloom plants to study and showed that they have problems with disease and with shapes.
We do understand the commercial problem of having hard-skinned fruits that will ship easily but we are lawn-chair gardeners, concerned with local farmers being able to offer good products at farmers markets. We think this concept of grafting on rootstocks has a lot of promise. Chemicals sent up through the graft can increase both disease and insect resistance—once Charlie and Kiki work out the best processes. In a few years they will probably print leaflets explaining the grafting system and what works best on what. You will probably have to make the grafts yourselves. It is hardly possible that the garden centers will have grafted transplants of the exact variety that you like—there are too many choices.
While we are still dreaming, we wish the twenty-first century plant breeders would be able to concentrate on improving those heirloom plants so that the fruit will still be soft, juicy, and tasty but with improved shapes and sizes. A big, round, vine-ripened fruit is much better for salads and sandwiches.
Now, we have one more topic; the one addressed in the title. For reasons unknown to us, tomato plants usually quit flowering after the first cold snap. It may be a light frost that burns a few leaves but the plant seems to go to sleep. Fall tomato crops do fine in the cooler weather but we hardly ever get vine-ripened tomatoes for Christmas. A research team in Holland—where the weather is usually pretty cold—is working with several varieties of a tomato plant species that grow well in the high Andes. They are grafting seedlings of greenhouse tomato species onto these rootstocks with the primary goal of reducing the energy requirements for keeping the greenhouses warm enough. So—we see possibilities for extending the Louisiana production time of fall tomato plants—vine-ripened fruits for Christmas. On the other hand, climate change might give us Christmas tomatoes without any research.
Ed O’Rourke, Jr. and Leon Standifer are the authors of Gardening in the Humid South (LSU Press, 2002), now available in affordable paperback.
