mardi 1 septembre 2015

52- The spirit of plants -2- Self defense


A couple of scientists at the University of Missouri, Jack Schultz and his wife Heide Appel, studied for over thirty years something that every grassed garden owner knows well, the smell of fresh-cut grass.
A crazy idea, you think? Not so sure, because all plants produce an odor when cut, pruned or aggressed. It was finally quite logical that someone try to understand why. The discoveries that these scientists have done are quite surprising. See the article published by Cody Newill in (in English)

"The smell of fresh-cut grass is the grass crying for help." Indeed, Jack Schultz explains that "one of the kinds of chemicals that plants produce when they are bieng attacked by insects are called volatiles or odors that travel through the air."

This is a signal whose purpose is primarily to attract predators such as birds or other predatory insects, telling them "come here to eat, there are caterpillars for you here."
At the same time, the assaulted plant synthesizes toxins and repellents (nicotine, caffeine and mustard oil) to reduce the intensity of attacks.
The plant does not know how to determine who or what is the aggressor. In principle, such an attack will be due to caterpillars or other insects. It therefore calls for help when you cross the lawn mower, thinking that you are a kind of big (and noisy) caterpillar.
Jack Schultz's team also tried to subject the plant to vibrations, similar to those produced by the caterpillars in the process of feeding (at the beginning of the article, you can listen the sound of the caterpillar eating). The plant then produces up to 35 times more toxic molecules. In other words, forewarned is forearmed.
I don't know if the plant makes the difference between the vibration of a caterpillar eating it, and the vibration of a cow grazing it. I suppose that the plant will not react the same way facing a ruminant. If I find studies on the subject, I'll let you know.
But it goes further because this signal is also used to warn its congeners of the imminent danger, so they set off their self-defense systems. A kind of vanguard who sacrifices itself for the good of the entire population. A beautiful example of vegetal solidarity (or of instinct of survival of the species).

In another article, also in English, written by Jessie Rack and published on,  we learn that what makes the flavor of wasabi or mustard comes from a progressive evolution of plants in their ongoing struggle against their aggressors. The work of Chris Pires and his team, again at the University of Missouri, on the "evolutionary arms race", shows that the plant has developed defense systems that insects have learned to circumvent. The plant, in response, has strengthened its defenses, and so on, until today, when varietal selection made for nutritional and agricultural needs, has sorted in the range of present characters present, to choose those of interest for humans . But the natural chemical compounds that are of particular flavors in some cases (mustard), irritants (pepper, chili) or toxic (hemlock, datura) are primarily defense substances against the aggressors.

A wasabi field in Japan

Finally, to close this exciting and gigantic chapter, another article, also in English, written by Nathanael Johnson and published on August 25 on -Technique-in-town-and-its-cleaning-up / , is speaking about an interesting consequence of previous researches.
22 years ago, an entomologist, Zeyaur Khan, in Kenya, invented a method of cultivation, he called push-pull, intended to enable local farmers to produce corn without suffering, one hand, the disastrous consequences of the attacks of borer caterpillars, and competition from invasive local grass, Striga, or witchweed, on the other hand. Local farmers, uneducated and poor, could not have recourse to pesticides. The technique, developed after many observations of flora and fauna, combine corn as main crop, with elephant grass (Pennisetum purpureum) and desmodium. Elephant grass has the particularity of being much more attractive to corn borer while being able to kill the caterpillar. Desmodium has the particularity of being an insect repellent and is toxic to the seeds of certain herbs, including striga.
The technique, the effects of which are controversial because its efficacy is not constant and difficult to translate to other crops and other regions had the merit of considerably improving the income of these farmers. It is also a line of work and reflection for possible changes in farming methods in the future.
 A field of corn, devasted by striga (foto FAO)

There are many studies worldwide that show that, ultimately, we don't know much about plants.
Gradually we discover an impressive world of plants, which surprises with its organization and untill now its unsuspected capacities. A likely route of future will learn how to boost the plant so that its self-defense capabilities are better expressed, and enable the farmer some interaction with its cultures.
Maybe we could get to reduce the need for pesticides and fertilizer giving greater protagonism to plants. In a way, the plant would produce and the farmer would become a plant shepherd.
But beware, this perspective is very beautiful, and probably unrealistic, as there is much to learn.

A small news item, published on August 24 in the web page,   tells us (in Spanish) the following sad story (literal translation):
"A German of 79 years died after consuming a zucchini of home production that has probably developed itself a toxic substance. It does not usually occur with zucchini, but in some rare cases, it can happen. The man and his wife were very ill for two weeks after they consumed zucchini, and eventually were transported to the hospital. The woman could be saved but the man's condition continued its deterioration, and finally he died.
The culprit of the poisoning is a substance called cucurbitacin that was naturally present in zucchini and cucumbers to avoid that animals eat them. Over the centuries, producers have managed to eliminate the substance through breeding programs, but if one grows his own vegetables, the substance may reappear. It is therefore recommended to test a piece of raw zucchini if it comes from home production. If it tastes bitter louder than usual, this may indicate the presence of cucurbitacin. The same is applicable to pumpkins."

What should we learn from this story?
What connection is there between the beginning of the article and this sad final anecdote?
Simply that if the plant has to defend itself, it produces, in unusual amounts, very natural toxins, designed to remove or kill the attackers. These toxins are present in the plant for some time, and in a unknown quantity.
Assuming that in the future, we will be able to interact with the crop and ask him to defend itself to avoid pesticide needs, it will be essential to be also able to know all the toxins emitted, and  to measure the quantity of each one before consumption of the food.
And we go back through these byways, to a point which I have already mentioned and which continues to concern me greatly:

Organic farming in all its variants refuses the use of synthetic pesticides. But it uses, except biodynamics, a large battery of biological pesticides, which are natural toxins dangerous to health. It also uses several self-defense stimulators, which are precisely what I'm talking about today. But now, the legislation does not oblige to declare all the components of biological pesticides, or to know the toxins that develop when plants begin in self-defense, let alone to control their residues on foods released for consumption. In other words, organic products, that consumers buy peacefully and with the support of authorities, are potentially more hazardous than conventional products, though often accused of poison carriers.
Another point worth raising: the famous self-produced seeds by the farmer or gardener, or purchased from the seed grower. This is an important element of the current debate. This anecdote gives a very interesting argument in favor of certified seed. Because even if the case is fortunately exceptional, we are in the situation of self-selected seeds, which escalated over time, turning "in the wild" by producing in large quantities, self-defense toxins. This phenomenon would not have occurred with a certified seed. We are in the presence of the very good example of what can make a controlled seed in food safety terms.

It is an excellent illustration of the saying "all that glitters is not gold," which may be translated in this case as "the most dangerous products are not necessarily those one believes".
To conclude, I would say the same thing for an animal you want to adopt. Take care, these plants in your garden or your vegetable garden are domesticated wild plants. At any time, its wild instincts may surface. In particular, never let your garden being invaded by insects or diseases. It seems unimportant to you because you are ready to eat ugly fruits and vegetables, since it comes from your own garden? Yes, but plants will look to defend themselves because it is in their wild nature. It is possible that they begin to produce toxins that you don't even suspect the existence, and that the food you are going to pick with confidence and pride, are in fact dangerous.
You want to make your garden? No problem, but be careful, take good care of it, so is your health.

I urge you to listen, at the beginning of the first article mentioned, the radio interview of Heide Appel and Jack Schultz. It's very clear and informative.

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