MadSci Network: Botany
Query:

Re: Why aren't beneficial plants as hardy as weeds?

Date: Mon Jan 25 13:30:40 1999
Posted By: Hurley Shepherd, Agricultural Research, USDA Southern Regional Center
Area of science: Botany
ID: 916469758.Bt
Message:

It is altogether proper for you to lament the plight of the poor cultivated plants. It is a problem which is not their fault!

Plants are exposed to all kinds of stresses in their daily life: getting enough water, getting too much water (flooded), bacteria, viruses, insects, molds, animals eating them. It is truly amazing that plants can survive at all. Wild plants (weeds) take on the world and usually win-- just look at the green forests and grasslands. They use a variety of defenses to survive.

They are covered with a waxy cuticle to keep them from drying out. This also prevents the entry of bacteria, viruses, and molds, and also slows down eating by some insects. Plants also make a variety of chemicals to stop herbivores from eating them. The tannins in tea and other plant parts which make you pucker also make it unpleasant for the plant to be eaten and thus offer some protection.

There are also very specific defenses in many plants. A relative of potatoes makes an alarm signal (pheromone) of the insect which feeds on them so they just stay away. As the old commercial said, " They don't bite, they don't even light!". Another plant releases a chemical which attracts the killer of caterpillars which are feeding on it!

Why are our cultivated plants so wimpy? Actually, they are not so bad, just not as good as their wild relatives. They can still resist most attacks. The problem is in the cultivation process ("artificial selection") as compared to natural selection. In nature, it's survival of the fittest--if a plant gets eaten or dies of an infection, it leaves no offspring to pass its genes along. Only the best combinations of genes are found in the next generation.

When people began cultivationg plants, they used different criteria than mere survival. We want the biggest, juiciest fruit, prettiest flower, largest leaves, most bulbous roots. These plants do not always have the best survival characteristics for growing in the wild, but it doesn't matter because we will take care of them.

The problem is, as your original question implied, they are getting so far away from their wild relatives that it is getting harder to take care of them. The good news is that the process is going back in the other direction, with plant breeders and other scientists looking at the wild relatives of crop plants to see if some of their survival genes can be incorporated back into crop plants. Watch for stories about this in your local newspaper or in science magazines. This is an ongoing process.

To read about research on the attraction of caterpillar parasites go to The American Society of Plant Physiologists(You can also search for other topics at this same site).

The story on the wild potatoes is in the scientific journal Nature, volume 302, pages 608-609. 1983. This is my favorite plant defense story.

An very interesting article on plant defense mechanisms from Scientific American can be found at http://www.uky.edu/~garose/ link100.htm (including plants which produce cyanide, animal hormones or hormone blockers, digestion inhibitors, or warning signals for nearby plants)


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