Did you know that hybrid vegetables can be toxic? If you are a strong proponent of heirlooms you are probably jumping up and down with joy and if you grow a lot of hybrids you are probably wondering if I have lost my marbles! Let me be clear, most hybrids are perfectly safe to eat, but there are a few special cases where they are not safe.
Understanding these cases of toxic hybrid vegetables provides insights into the risk of saving seeds and using natural means to develop new cultivars.
What is a Hybrid?
The term “hybrid” is used two different ways. Some consider a hybrid as being the result of crossing two specific cultivars to produce special seed. For example, my favorite tomato is the Sweet 100, which is a hybrid seed produced by hand crossing two specific cultivars.
There is also a more general use of the term where a hybrid is the product of crossing any two individual plants. This could be man-made or the result of an open-pollinated cross. Any gardener who is crossing two plants is producing a hybrid and most naturally produced vegetable seed in a garden is also a hybrid.
The alternative is the heirloom. It is a plant that has been line bred for some 50 years resulting in a stable cultivar. Crossing two individuals of the same cultivar is not considered to be a hybrid, although technically such a cross does produce a hybrid because two individual heirloom plants are not 100% identical from a genetic perspective.
This blog uses the more general use of the term hybrid.
All Vegetables Are Toxic
That heading might surprise you, but the only way a plant can fend off pests is to produce natural pesticides and plants make thousands of different ones. Many of them are not only toxic to pests but also to us. 99.9% of the pesticides we eat are these natural pesticides.
Why don’t these pesticides harm us? There are two important points to understand. First, the level of these pesticides is quite low and so they do not harm us, at least they don’t harm us enough to cause a concern. The second point is that we have evolved eating fruits and vegetables for a very long time and our bodies have developed great mechanisms to overcome these toxic substances.
When Breeding Hybrids Goes Wrong
Almost none of the vegetables we eat today resemble wild versions of the food. Humans have been breeding and improving them for hundreds, if not thousands of years. This is usually done in one of two ways. We play god and move pollen from one plant to another to see what happens. We then select the best offspring and repeat the process, over and over again.
The second option is to let nature do her thing. We just harvest seed and keep an eye out for the best plant. Then we collect seeds from it, and do it all over again the following year.
Both methods produce food with desirable features, such as large size, good taste, easy to grow and pest free. Why would the new, better hybrids be pest free? In many cases it’s because the selected hybrid produces more natural pesticides. If the amount of pesticide is just a bit higher we end up with a plant that is pest free but still good to eat. If things go wrong, the hybrid has such high levels of natural pesticide that it becomes toxic to us. Let’s have a look at some of these cases.
The Toxic Lenape Potato
Potatoes are part of the night shade family and they all produce toxic alkaloids (glycoalkaloids). The amount found in commercial potatoes is normally low enough that we can handle them. If you allow potatoes to sit in the sun, the skin gets green while at the same time building up the level of an alkaloid called solanine. At some point the amount is high enough that it is toxic to us and it should not be eaten.
In an effort to produce a great potato for making chips, breeders used conventional breeding methods to develop a variety called Lenape. After a successful commercial launch, it was found to have a dangerously high level of solanine and was removed from the market. It did make great chips though! The average Russet potato contains about 8 mg/100 g of solanine while the Lenape has 30 mg/100 g. The Lenape potato is still used for breeding because of it’s pest resistance, but offspring are tested for alkaloid content, as are most new varieties of potatoes.
A similar high-solanine potato was removed from the market in Sweden in 1995. In this case the cultivar was a heirloom variety developed in the UK in the nineteenth century, called Magnum Bonum.
A hybrid potato produced from two species, S. tuberosum and S. brevidens, produces the normal alkaloids but also a new toxin called demissidine, which was not present in either parent. Traditional breeding methods were used to create this hybrid, illustrating the danger of mixing thousands of genes together without controls. This is something the anti-GMO crowd needs to understand.
Celery naturally produces toxic chemicals called psoralens, which helps it fend off insects and some diseases. These are natural products that are also found in limes, lemons, bergamot, parsley, figs, and cloves. Celery plants that contain higher levels of psoralens are not chewed up by pests and are therefore more appealing to consumers, so breeders inadvertently select for high levels. If celery suffers disease or has been bruised it can produce up to 100 times the normal level of psoralens. Unfortunately, such celery produces photodermatitis in workers handling the product, both in the field and in grocery stores.
Psoralens are also responsible for the allergic blistering caused by giant hogweed.
Kiwi fruit, sometimes call Chinese gooseberry, is one of the newest types of fruit on the market. The original plant was edible but unpalatable until breeders in New Zealand turned it into the fruit we know today. There is no evidence that it has ever undergone any kind of premarket safety analysis. Recently, an allergenic protein (actinidin) was isolated and characterized (1998).
When someone has a kiwi allergy, their immune system reacts negatively to substances in the fruit and they often experience allergic reactions to other foods, which is known as a cross-sensitivity. They can even become allergic to latex gloves. This allergy can be severe and can cause anaphylactic shock.
Toxic Squash Syndrome
Cucurbits like cucumber and zucchini produce a bitter tasting compound called cucurbitacins. These fruits are normally grown so that they contain low levels of cucurbitacins since people don’t like the taste. When curcurbits cross pollinate with each other the seeds can produce hybrid plants that have unusually high levels of cucurbitacins. When eaten, they cause a form of food poisoning called toxic squash syndrome, which can cause nausea, vomiting, diarrhea and even hair loss.
The fruit produced by such pollination is safe to eat. However, the seeds from such fruit may produce a plant that has toxic fruit. If the fruit tastes bitter, it should be discarded.
Toxic squash syndrome seed can also be found in commercial sources. Mr Fothergill’s, a seed company, had to recalled a batch of Courgette Zucchini that could contain seeds which produce bitter tasting fruits.
Hybrids vs GMO
There is a strong belief in some circles that GMO caries a much higher risk compared to traditional breeding or “natural” pollination done by bees. Once you understand that conventional breeding is much less targeted and has much less testing and oversight, you begin to understand why so many scientists agree that GMO is a safer alternative.
Are Hybrids Safe?
Are you now scared to use hybrids? Don’t be. The point of this post is not to scare you, but to make you aware that natural breeding can produce toxic food.
What about heirlooms? If the gardener controls the cross breeding, and insects don’t get in the way and do things wrong, heirlooms might be slightly safer, but I assure you most gardeners do not take the precautions needed to guarantee that no unscheduled cross pollination takes place. In practice, saving heirloom seeds from most crops is not any safer than using hybrids.