Genetics for Seed Savers FAQ


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How do I hand-pollinate a flower?

How much separation do I need in order to save seeds without cross-pollination?

How many seeds saved from an F1 are likely to produce something like the F1, something like the parents, or something like trash?

How do I hand-pollinate a flower?

Answer depends on why? To make sure something like a squash or melon sets fruit, just use a male flower like a paintbrush, and paint the stigma with pollen. See flower structure.

To make a controlled pollination, either a self for seed saving purposes, or a cross for experimentation, see how F1s are made. The process is the same for a self, only you do not need to worry about self-contamination, therefore no emasculation is necessary.

To make selfs for seed saving purposes, sometimes it is as easy as bagging a perfect flower and shaking it to spread pollen after anthesis. Favorite example is squash (monoecious, imperfect, protandrous usually). Protect male and female from contamination, use male flower after anthesis as paintbrush, paint stigma, protect female flower to avoid cross-pollination, label stem of female flower so fruit can be identified later.

How to hand-pollinate depends on the flower. Some are simple, some are not. Again, there are practical differences depending on what you are trying to do. Many flowers are practically impossible to hand-pollinate because of structure (composites, saxifrages). In practical breeding of these, sometimes the simplest solution is to give up control, and do fertile by fertile crosses, and then try to sort out the progeny. This won't work for genetic studies, but for breeding, it's sometimes the most efficient way to work.

Hand-pollination also requires pollen to be available when the flower is ready to be pollinated. That's not always easy. Think about early vs. late crosses. See pollen collection and storage.

Avoid contamination. If using brushes, sterilize them in between pollen gathering. 70% ethanol is typical. that's 140 proof. grain alcohol diluted 7:3 with water. 50% (100 proof) is not effective, so do not use vodka as a substitute. Buy a pint of grain alcohol. More is not better. 80% is not as effective as 70%, and 100% is much less effective than 70%. The water seems to be necessary.

How much separation do I need in order to save seeds without cross-pollination?

There is no easy answer. It depends on the species. See IB vs. OB. You can save seed from an IB species with little or no isolation required. ex. lettuce, legumes, tomatoes, eggplant, and peppers. Peppers are interesting: the current trend in hot peppers has brought many "wilder" types into use, and these tend to be more OB than IB. These therefore need more isolation, but a insect-tight bag over a flower should do.

OB species need isolation. You can do this by only growing one variety of each species (remembering that there are lots of Brassica species, and that they will cross freely). You can hand-pollinate if the species is amenable (like squash or melons). How much isolation? Commercially, the recommendation is on the order of 1000 to 1500 ft minimum. In field produced flowers, isolation plots in California use canyons.

These vegetable species require little if any isolation for seed saving: dry beans, snap beans, lima beans, soybeans, eggplant, lettuce, peas, peppers (bell), and  tomatoes.

These vegetable species require isolation (controlled pollination, or single variety) for good seed saving:  basil, beets, broccoli(1), brussel sprouts(1), cabbage(1), cantaloupe (2), carrots(3), cauliflower(1), chinese cabbage (4), chives (5), cucumber (6), dill, endive, favas(?), fennel, garlic chives(5), gourds (7), kale (1), maize(8), muskmelon (2), onion, parsnips, pumpkins (7), rutabagas (1, 4 check species), spinach (??), summer squash (7), winter squash (9), and watermelons (10).

Note 1:  Broccoli, brussels sprouts, cabbage, cauliflower, and kale will cross freely. Only let one of these flower if you are trying to save seed.

Note 2: Cantaloupe and muskmelons will cross freely.

Note 3: Carrots and the weed queen anne's lace will cross.

Note 4: Chinese cabbages of all kinds may cross, but should not cross with the brassicas listed in Note 1.

Note 5: Chives and garlic chives will not cross, nor will they cross with onions.

Note 6: Cucumbers will cross freely between picklers and slicers. They will not cross with any of the melons.

Note 7: Small gourds, pumpkins and summer squash will all cross freely. Large (birdhouse) gourds are a different species and will cross with nothing else in the garden.

Note 8: Sweet corn will cross freely with field corn, popcorn, or any of the ornamental corns.

Note 9: Hubbard type winter squash will not cross with butternut types, and neither will cross out to the types listed in Note 7, nor will any other squash cross out to a true cushaw squash.

Note 10: Watermelons will not cross with cantaloupe, muskmelons, cucumbers, or any of the squashes, gourds, or pumpkins.

How many seeds saved from an F1 are likely to produce something like the F1, something like the parents, or something like trash?

There is no easy answer. It depends on the species, and it depends on how many you are growing out. The more you grow, the more likely you are to see variation.

It is a population genetics game. See Mendel Lives! for some background. The real issue is how many genes you are trying to follow, and whether or not those genes have dominant alleles. If all you want to recover is a red-fruited tomato, then almost all of the seeds you save will give you what you want. But if you want a red-fruited, globe-shaped, determinate, early-fruiting, disease-resistant, etc. etc. and the original parents differed in those characters, then you might not be able to find many plants that appeared to match the F1. Some would be close; yes, but identical?; probably none, unless you grew out a huge population, and then how could you identify that one that was identical to the F1?

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