I've done some more serious studying on the traits required to breed a cold tolerant tomato. One of the basic problems to overcome is that most tomato plants do not flower below about 60°F and as the temperature drops further the leaves lose efficiency, the roots become ineffective at absorbing potassium and phosphorus, and leaf chlorophyll tends to drop causing the leaves to become distinctly yellow. I'm going to presume that each of these traits can be addressed.
The CBF pathway is the basic cold sensitive biopath that allows a plants in the tomato family to respond to cold temps. From one of the articles that ChrisK posted in the Winter Reading thread, this pathway can be ramped up by a cross with LA3969 which is an introgression line containing part of chromosome 12 from S. Habrochaites. I have therefore asked TGRC to add this line into my shipment.
The root efficiency issue is going to be difficult. I have not found any documentation showing increased root efficiency at low temperatures for any known lines of tomato. I am going to lean heavily on the S. Lycopersicoides IL's (introgression lines) to provide some genetics to address this. I will also have some other possibilities from seed which Frogleap sent me of an L. Peruvianum line that seemed to have significantly improved root strength and structure.
There are two distinctive high level traits that I must improve to develop a cold hardy tomato. One is the ability of a tomato plant to continue growing at low temps. The other is the ability of foliage to withstand overnight freezing temps. The two traits are complementary, but not necessarily linked. I will therefore have to take some special steps to identify plants that exhibit both capabilities.
My first thought was to simply place some plants outside when the temp is going to be between 32 and 55 degrees. But I can't control these conditions well enough to really tell a difference. So my second thought is that I can set up a shelf in my refrigerator to place plants so they will get about 12 hours at 36 degrees and then be placed under lights for 12 hours at 72 degrees. If continued several days, this should result in some plants showing an ability to grow even when regularly exposed to low temps.
The next issue is to find a way to test plants at freezing temps. I can easily pick a night when the temperature is going down to about 25 degrees to put the plants outside. The problem I foresee is that frost will form on the leaves which will kill them. I want to find plants that will withstand freezing temps, which does not necessarily mean that the plants can also stand having frost form on the leaves. If the wind is blowing, then frost does not normally form. If the plants are covered with floating row covers, then the frost forms on the row cover but not on the plants. Another option is to turn my refrigerator down so it hits 25 degrees and equip it with a small dehumidifier to prevent frost. With a setup like that, I could completely control the conditions the plants are exposed to.
There is lots more thinking and planning to do and quite a bit more reading of articles about cold tolerance and tomatoes.
DarJones
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