Cytoplasmic male sterility (CMS) is widely used in both conventional and organic agriculture as a simple inexpensive method of creating hybrids and protecting seed company's trade secrets. Sterile plants are problematic for landrace gardeners and seed savers because they interfere with normal plant biology and seed saving practices.
Male sterility can be achieved by unusual natural means or by genetic engineering. Last week's blog defined cell fusion CMS and touched on the politics of using genetically engineered varieties in USDA organic seeds and food. This week's blog takes a pragmatic hands on approach to sterile plants and treats all male sterile plants the same whether they originated by natural means or in a genetic engineering laboratory. On my farm I have banned male sterility of both types in annual and biennial crops because I think that it is wrong to propagate defective plants.
Approximately 85% of the USA carrot crop are F1 hybrids that are male sterile. They do not produce pollen. What this means from a practical standpoint is that if a home gardener plants one of these carrot varieties and tries to save seed from it that their attempt will be unsuccessful. Either no seed will be produced, or some wild pollen from Queen Anne's Lace will pollinate the crop and the offspring end up reverting to wild forms, or the plant will be pollinated by other nearby carrot varieties.
When I started my carrot landrace I used a mix of hybrids and open pollinated carrots. After I became aware of cytoplasmic male sterility I screened my carrot crop and found that 70% of my plants were male sterile. I was crushed, and incredibly disillusioned with myself, with the seed industry, and with my trading partners that unknowingly provided the seed.
This week I reviewed the seed offerings of 6 seed companies that were suggested to me as having low rates of cell fusion CMS. Half of the companies offered inventories that seem like they have a lot of male sterility. One of them claimed to be 100% organic and a signer of the safe seed pledge. It seems to me that about half of it's inventory on some species was made by cell fusion genetic engineering! One company didn't disclose whether or not the seed they are selling is hybrid but they are offering varieties with the same names that the other companies are calling F1 hybrids so they are likely the same varieties and made with cell fusion CMS.
Half of the companies I reviewed offered only open pollinated seeds. They are doing seed right for home gardeners. If I still bought seeds I would only buy from those companies.
The take away message for me is that I can't trust the seed industry and my swap partners to tell me whether or not the seed they are offering is male sterile. I figure that they either don't know what they are trading or they know and don't want to tell me. Fortunately I don't have to rely on other people to do the screening for me. If a plant fails to produce pollen it is often obvious by looking at the flowers with a magnifying glass or even with just my eyes.
Male sterility takes many different visible forms depending on the species, but one thing that is fairly common among them is that the anthers are missing from the flower. This week's images show what that looks like in the cabbage family and in the carrot family.
Nowadays I routinely screen for male sterility and chop out every sterile plant that I find.
Male sterility is common among commercial hybrids in the carrot, beet, onion, sunflower, and cabbage families. I don't knowingly add hybrids from those families to my landraces. I think that last growing season I finally eliminated male sterility from my carrot patch. Healthy carrot flowers look fuzzy even from a distance because of many anthers poking up. Sterile carrot flowers look smooth because the anthers are missing. I have included photos in this blog of what that looks like.
Commercial hybrids of cabbage family plants are often made by cell fusion CMS. They are crops like broccoli, kale, turnips, radishes, bok choi, rutabaga, mustard, cabbage, Brussels sprouts, cauliflower, canola, and kohl rabi. A normal cabbage family flower has styles with anthers attached growing from the center of the flower. A common manifestation of male sterility is that the anthers and styles are missing. Look at the drawing of a broccoli flower to see what that looks like.
In onions, male sterility is often indicated by bulbils forming in the flower head. The flowers might produce anthers, but they don't release pollen. If I rub my fingers across a normal onion flower it will come away with pollen on it. Sterile plants don't produce pollen. Seed set is often low in male sterile onion flowers.
In potatoes with male sterility the pollen is often sticky. It is like a jelly instead of a fine dust. I can observe dusty pollen by flicking a flower with my finger on a sunny day. Pollen pours out of healthy flowers.
I don't know what male sterility looks like in beets or chard. I suppose that male sterile plants wouldn't release a cloud of pollen when shaken.
Another way that I commonly identify male sterile flowers is to pay attention to the pollinators. Flowers that are not producing pollen are less attractive to bees, flies, wasps, and other pollinators. What self respecting sweat bee is going to visit a pollen-less sunflower? Additionally male sterility often interferes with the nectaries of flowers causing them to produce little or no nectar. Another turn-off to pollinators.
Seed set is often much lower in male sterile plants than in plants with healthy flowers. In the case of a single variety being planted with no related healthy plants within pollination distance the variety might self-eliminate by failing to produce any seed at all.
In spite of contamination of the conventional and organic seed markets by genetically engineered cell fusion CMS, it is simple to participate in survival-of-the-fittest and farmer-directed selection in order to create healthy locally-adapted populations of food crops that are free of male sterility. This is part of the reason why I believe that landrace gardening is a path towards food security through common sense and traditional methods.
Joseph Lofthouse grows vegetables in a cold mountain valley where he practices the art of landrace gardening in order to feed his community more effectively.