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Towards Promiscuous Wild Tomatoes

I am Joseph Lofthouse, a subsistence farmer from a cold mountain valley in the Rockies. I am known for my advocacy of landrace gardening: that is growing genetically diverse, cross-pollinating crops for enough generations in the same location, that they become locally-adapted to the ecosystem and to the community’s habits.

One of the strengths of landrace gardening is that the crop’s genetics are rearranging themselves to figure out ways for the plants to solve their own problems, rather than depending on human intervention.

Growing conditions for warm-weather, long-season crops are challenging in my high-altitude mountain valley. The first landrace that I grew, Astronomy Domini sweet corn, quickly adapted to my farm and has grown consistently well ever since. I was enamored by it and converted every species on my farm to the landrace growing system.

With more than 70 species converted to landraces, I observe that landrace growing works best in genetically diverse populations with some degree of crossing. The rare crossing events in mostly inbreeding species can produce amazing hybrid vigor that often favor offspring of crosses over inbred ancestors. I didn’t observe much hybrid vigor among tomatoes. I believe it is because domestic tomatoes are so closely related to each other that there is barely a hint of diversity left in them. I was able to do a modest amount of selection for quicker maturity, and more cold tolerance, however, variety improvement was not as dramatic as what I observed with other species.

Domestic tomatoes are one of our most highly inbred crops. During domestication, a few seeds were carried from the Andes to Mexico. Then a few seeds were carried from Mexico to Europe. The seeds left Europe to travel to the rest of the world as the crop that we know today. Each leg of the journey created genetic bottlenecks, and domestic tomatoes lost much of their ancestral knowledge about how to deal with pests, diseases, soils, and farmer’s habits.

Each time tomatoes traveled to a new location, their accustomed pollinators didn’t make the trip with them. Tomatoes adapted by becoming self-pollinating most of the time. That contributed to domestic tomatoes becoming even more inbred, and losing more diversity and ancestral intelligence.

Then, the heirloom preservationists started multi-decades long inbreeding of varieties. Tomatoes were subjected to intense selection against flower traits that might lead to inadvertent cross-pollination. Tomatoes became even more inbred, and even more unlikely to experience cross-pollination. Many varieties lost flower traits that might facilitate occasional crossing.

While conducting frost/cold tolerance trials on tomatoes, I noticed one variety that had bumblebees on it frequently. They weren’t much interested in any other tomato. As a landrace facilitator, I marveled at how wonderful it would be if bumblebees would make natural crosses between my tomatoes. Ongoing genetic re-shuffling is super helpful when creating locally-adapted varieties that can adapt to changes in the ecosystem. If bees are making hybrids for me, that saves expense, time, and record-keeping.

Therefore, I started selecting for plants with more promiscuous flowers: larger petals, brighter colors, open anther cones, exerted stigmas, bolder floral displays, etc. (Please see attached photo for a comparison of a wildling blossom vs a domesticated tomato blossom.)

Then I grew a wild tomato, Solanum habrochaites. Wow! The flowers were dramatically promiscuous. An order of magnitude more promiscuously shaped than the domestic flowers. Many species of pollinators find the flowers highly attractive. And even better, the plants cannot pollinate themselves! They have to be pollinated by a plant that is not closely related. Every seed is a new auto-generated F1 hybrid in every generation. They are a plant breeder’s dream! The population automatically favors genetic diversity, and it becomes trivial to trial hundreds of thousands of constantly re-arranging genetic combinations for resistance to problems like blights, insects, soil, climate, etc.

My current approach to tomato breeding is to bring a few genes (mostly regarding fruit size) from domestic tomatoes into populations of wild species. The wild species have retained the ancestral genetic-knowledge that allows them to solve their own problems, which farmers are currently trying to solve with chemicals, materials, techniques, or labor.

I’m expecting to write a series of posts for the World Tomato Society to explore the theoretical and practical aspects of growing promiscuously pollinating tomatoes.

Joseph Lofthouse 🍅
Author, Speaker, Landrace Farmer

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