In previous blogs I have written about landrace development projects that I have been working on for years. Today I am describing a project that is just beginning. I would like to convert my tomato population into a promiscuously pollinated landrace. A freely cross-pollinating population of tomatoes would greatly simplify the process of survival-of-the-fittest selection for families of tomatoes that thrive in my garden.
In their natural non-domesticated state, tomatoes are a promiscuously pollinated crop. During domestication they were converted into a highly inbreeding crop. I believe this is due partially to not taking the tomatoes natural pollinators with the plant when it left its native land, and partly due to the intense focus in the last century on preventing cross-pollination. Naturally cross-pollinated tomatoes are typically considered a liability in modern times both in mega-ag and among home growers so heavy selection pressure has been put on the species to eliminate traits that lead to higher cross-pollination rates. I intend to reverse that trend in my garden and to create a landrace of tomatoes that is promiscuously cross-pollinating.
What Triggered This Project?
During the 2013 growing season I conducted a cold/frost tolerance trial on tomatoes. That got me into the tomato patch regularly to take measurements and photos. While there I noticed that just about every time I was in the tomato patch that there were two plants, out of 50 varieties, which were highly attractive to bumblebees. At least 5 different species of bumblebees visited the plants while I was watching. They spent around 10 seconds per flower. If the bees even visited other tomato plants they stayed for less than a second on any particular flower. Those two plants also happened to be the most productive plants in my garden. The varieties are named Jagodka and Nevskiy Red. I attribute the high productivity in part to the bumblebees doing a highly effective job of pollinating the flowers on those plants. I believe that more flowers got better pollinated leading to higher fruit set and larger tomatoes. That got me to thinking about what I really want out of my tomatoes. Do I want to continue trialing highly inbred varieties from far away that perform marginally? I decided that doesn't work for me any more. I want a locally-adapting population of tomatoes that is constantly generating lots of natural hybrids so that they can get more and more acclimated to growing in my garden with its unique pests, soil, climate, and farmer.
Where Do I Go From Here?
I have identified two varieties that are highly attractive to bumblebees, and that were very productive in my garden. They will form the basis of my new population. For the next few years the primary selection criteria for my tomatoes will be 'Highly attractive to pollinators'. Secondary selection criteria will include 'children of natural cross-pollination', productivity, and 'traits that might lead to higher cross pollination rates'.
Some of the older heirloom-type tomato varieties have retained traits that make cross-pollination more likely. I intend to gather some of those varieties together and allow them to cross-pollinate if they will, and select among the offspring for plants that are highly attractive to pollinators.
Possibly Useful Traits
Last summer I used a 20 X magnifying glass to carefully examine tomato flowers. I noticed a number of traits that might be useful in this project, especially if all of the traits could be combined into a single family. If a couple of years of natural pollination and observant selection don't lead to the combining of these traits I may attempt manual pollinations later on.
Simple Flowers: Some varieties of tomatoes have so many layers of petals that they prevent pollinators from reaching the interior of the flower. I will be selecting for simple flowers that allow easy access by insects.
Non-Fused Anther Cones: There was wide variation in how tightly the anthers were fused together. In some varieties they were loosely connected if at all, and in others the anthers were tightly fused together. I believe that a non-connected or marginally fused anther cone might lead to higher cross-pollination rates.
Loose Anther Cones: Some anther cones were tight against the style. This tight fit might prevent pollen from reaching the stigma or from leaving the anther cone, thus leading to lack of interest by pollinators and low cross pollination rates. Other anther cones fit very loosely around the style. I will be selecting for loose anther cones.
Extended Stigmas: Some varieties had stigmas that were totally inside the anther cone, others had stigmas that were outside the anther cone, and everywhere in between. I expect to be selecting for long styles that are outside of the anther cone so that they can rub up against a bees belly and collect some foreign pollen. That requires that pollinators are attracted to the flower in the first place.
Abundant Pollen: I attempted to extract pollen from many varieties of tomatoes this summer. The two varieties that were attractive to bumblebees were the only two varieties in my garden that released clouds of pollen for me when vibrated. Bees are not dummies. If a plant isn't feeding them then they are not going to hang around. The trait of attracting bumblebees might be a sufficient selection criteria to use for developing a locally-adapted survival-of-the-fittest promiscuously-pollinating tomato landrace in my garden.
I'd love feedback on this project. Have you noticed specific varieties of tomatoes in your garden that are highly attractive to bumblebees or other pollinators? Do you know of any varieties that readily release clouds of pollen or that are unusually susceptible to natural cross pollination? If you notice a variety during the coming growing season that the bees just won't leave alone, please tell me about it. I have a small amount of seed from Jagodka and Nevskiy Red which the bumblebees really liked this summer. If you'd like to collaborate on a grow out or in making manual crosses with something like Hillbilly let's correspond.
I believe that there is plenty of diversity available among commonly available tomato varieties to allow a group of observant plant breeders to return a population of tomatoes to their natural state of being promiscuously pollinating. I believe that it is easily possible to combine modern traits like large fruits with ancestral traits like being highly attractive to pollinators and very susceptible to cross pollination. A tomato landrace that combined the best of both worlds would constantly be regenerating lots of new hybrid vigor. This is part of the reason why I believe that landrace gardening is a path towards food security through common sense and traditional methods.