PLANT GENETIC DIVERSITY 

" The earth was not given to us by our parents, it was loaned to us by our children." -- Kenyan proverb

What is plant genetic diversity?

As the world's population continues to grow, the corresponding increase in food need will depend more and more on the conservation and use of the world's remaining plant genetic resources.  Conservation and use of genetic resources might have originated at about the same time as agriculture itself.  Through the millennia, farmers have practiced the act of conserving seeds of desirable plants for future sowing, in essence, domesticating wild plants to suit their specific needs.  Historically, humans have used about 5000 plant species for food.  However, only about 150 species have been cultivated commercially around the world today.  Of the 150 species grown commercially today, only three species, rice, wheat and maize, comprised nearly 60 percent of the world's calories and protein supply.  Most of the loss in the number of cultivars being grown happened in the last few decades. 

In the past, the loss in genetic diversity of plants can be attributed to natural causes. Activities such as land clearing and burning, overgrazing, overuse of chemicals and war have destroyed the diversity of crop plant species relatives present in the wild.  However, the main cause of genetic erosion in recent years is due to human action. The large scale introduction of high-yielding plant varieties during the Green Revolution of the 1950s and 1960s, led to the abandonment of old, traditional varieties that had evolved through the years in farmers fields.  These new varieties often require irrigation and large inputs of chemicals which the old but lower-yielding traditional varieties that did not.  The switch to the new varieties also meant a dependence on fewer varieties being grown.  Thus, many of the world's most important food crops may now be vulnerable to changes in the climate or susceptible to new diseases and pests.  Read the website on # Genetic Diversity and food security.

The value of plant genetic diversity

The increasing dependence on the few plant species as food makes the state of the of the world's food supply even more vulnerable to sudden changes in climate or attacks from pests and diseases.  This was evident in occurrence of the Southern Leaf Blight disease that nearly destroyed the corn crop of the entire USA in 1970.  The uniformity of the corn crop allowed the blight to destroy about US$1,000 million of the crop and reduce yield by almost 50 percent.  Fortunately, a source of resistance to the blight was discovered in an African variety of corn called Mayorbella (National Research Council 1972).  This incident also highlighted the potential treasure troves of useful genes available in traditional varieties.  Tragically, these traditional varieties are often lost as development destroys habitats or when farmers abandoned traditional varieties in favor of modern ones.  This loss in genetic resources, if allowed to continue, will ultimately jeopardize our future food security. Read this USDA article on Crop Genetic Resources:  An Economic Appraisal # (required) .  Read Bioversity International Website on Agricultural Ecosystems # (required).

After completing Unit IV Section A, please click on Section B. 

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# - Represents a required reading

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