Understand Promiscuous Pollination in Landrace Gardening

Reader Contribution by Joseph Lofthouse
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Pile of farm fresh watermelon
Photo by Pixabay/paulbr75

Promiscuous pollination is essential to the long-term survival of landrace crops. Some species are very promiscuous. Other species are mostly self-pollinating, crossing occasionally.

Promiscuous pollination rearranges the genetics of the plants. Shifting genetics allows life to adapt to changes in the ecosystem or in farming practices.

Pollination is Highly Localized

A flower is most likely to be pollinated by the nearest compatible flower. The closer we inter-plant different varieties, the more likely they are to cross. I typically sow the barely crossing varieties jumbled together to get the most crossing possible.

The mathematics of pollination are quadratic, meaning that doubling the distance between two flowers cuts the chances of cross-pollination to a quarter. Increasing the distance tenfold lowers the chances of cross-pollination a hundredfold.

Pollen flow between flowers. Diagram by Joseph Lofthouse

Pollen flow is highly localized
Diagram by Joseph Lofthouse

The graph showing pollen flow between flowers applies at any scale. It applies to the separate flowers in the umbel of a carrot as it does between umbels on the same plant. It applies to separate plants in the same patch, and to separate patches in the same field.

An awareness of the highly localized nature of pollination allows us to design plantings to either minimize pollination for maintaining isolation distances, or to maximize it to encourage crossing.

Purity and Isolation Distances

People express fear about saving seeds. What if they flub isolation distances? What if a variety gets polluted? How about inbreeding depression? What if the seed is a hybrid? What about poisons and deformed monster plants? My response is that those things are of little consequence.

The essential knowledge regarding seed saving is that plants produce seeds. They can be harvested and replanted. For plant breeding, add that offspring resemble their parents and grandparents. Sometimes a trait skips a generation.

Growing Landrace Populations

Growing landrace populations greatly simplifies seed saving. It reduces worry about plant purity and isolation distances. Worrying about purity is one of the biggest impediments to seed saving. Maintaining purity leads to inbreeding depression. I don’t worry much about isolation distances or keeping cultivars pure. Plants are stronger when cultivars cross-pollinate each other. If a Hubbard squash and a banana squash cross-pollinate, the offspring are still squash. They grow like squash, they look like squash, they cook like squash.

When two great varieties cross, the offspring inherit greatness. People started domesticating plants up to 40,000 years ago. The vast majority of undesirable traits have been eliminated from domesticated crops. I don’t observe crossed plants turning into poisonous mutants. When two highly domesticated varieties cross, the offspring are likewise highly domesticated. The offspring’s traits blend those of the parent varieties.

Hybrid seeds
Illustration by Joseph Lofthouse

Troubleshooting When Plant Breeding Goes Wrong

Sometimes I make crosses to wild, less-domesticated parents. I hope to incorporate more diversity. Occasionally in those crosses, I find a poisonous fruit, or other undesirable traits. Melon, squash, cucumber, bean, and lettuce poisons are well behaved. They taste horrid. Terrible tastes are a good indication that a plant produces poisons. Nightshades might taste good, but the poisons make me want to barf.

I planted a “pocket melon”, which is a tiny cantaloupe with a perfume smell. I taste every fruit before saving seeds. The pocket melons tasted nasty! Poison in melons tastes horrid. I discarded the whole year’s seed crop. I couldn’t risk introducing poison into the cantaloupes.

When I introduced genetics from wild watermelons, the “exploding melon” trait appeared. If jostled while sun-warmed, the fruits popped open. Gradual selection eliminated the trait in a few years.

I consider tepary beans to be semi-domesticated. My original strains had a trait which I call “hard seed.” About 10% of the seeds wouldn’t absorb water when soaked. They would take weeks or months to germinate. I eliminated that trait by pre-soaking the seeds, and only planting those that absorbed water immediately. The wild watermelon brought the same trait with them, which self-eliminated. Watermelon is a full-season crop at my place. Plants that take a long time to germinate don’t reproduce before frost.

These days, if I choose to grow wild ancestors of domesticated crops, I grow them in a separate field for a few years. This ensures that they don’t introduce unfortunate traits. It’s easier to keep them isolated in the beginning, rather than eliminating a trait later on.

I keep hot peppers separate from sweet peppers. I don’t care what a sweet pepper looks like. It can be any shape, any color, or any size as long as it is not hot. The most important sweet pepper trait in my garden is: “must produce fruit.”

Considerations for Inbreeding Crops

For the mostly inbreeding crops like common beans and grains, I consider them isolated at 10 feet (3 meters) apart. With the mostly outcrossing crops, I consider them isolated at 100 feet (30 meters) apart. I observe around 1% to 5% crossing at that distance.

Crops flowering at different times don’t cross-pollinate. An early maturing and a late maturing corn may grow next to each other, without worry of crossing. That’s how I grow flour corn and sweet corn in the same field.

Likewise, inbreeding depression is only a problem when growing a cultivar in strict isolation. It doesn’t much matter how many plants are in the population if new genes arrive regularly. The inflow of new genes is counteracting the gene loss due to inbreeding.

I wonder if the “minimum number of parents” recommendations are a ruse by the mega-seed companies to discourage people from saving seeds. The standards necessary for growing a seed crop for the entire world are much different from what is required for growing local food for the local neighborhood. I’m not going to suggest magic numbers of how many plants to save seeds from. Save seeds from as many as is easy for you and your community. Be generous during selection. If a variety loses vigor, allow it to cross with something else.

I don’t care if there are a few percent off-types in what I grow. I’m harvesting by hand. I’m holding each vegetable in my hand before cooking. If I don’t like it, I compost it or feed it to animals.

Joseph Lofthousegrows vegetables in a cold mountain valley where he practices the art of landrace gardening in order to feed his community more effectively. Read all of his MOTHER EARTH NEWS posts here.

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