Genetic Diversity of Crops
Jan 20, 2025
Last week I discussed the importance of collecting genetic material for crop advancement and managing gene banks. This week I would like to continue with the discussion of plant genetics with a focus on genetic diversity. Genetic diversity refers to the range of different inherited traits within a species. In a species with high genetic diversity, there would be many individuals with a wide variety of different traits. Genetic diversity is crucial for a population to adapt to changing environments such as disease, insects, weather patterns, soil conditions, etc. Genetic diversity is akin to your retirement plan. A diversified retirement portfolio can minimize risk and typically provides the most reliable returns. When you invest in a mutual fund, you are investing in many different corporations in various aspects of the economy. By investing in a mutual fund instead of just one corporation, you are not putting all your “eggs in one basket.” If one corporation or sector fails in a mutual fund, it will not hurt too badly if the other sectors are doing well. However, if you invest solely in one corporation and it fails, you could lose everything. Genetic diversity provides the buffer for a species in a world that sometimes can be downright hostile.
Genetic diversity is very important in crops grown for food across the globe. According to the United Nations Food and Agriculture Organization (FAO), there are about 300,000 plant species that exist in the world today. 7000 plant species have been cultivated or collected for food at some point in the last couple of millennia. Today fewer than 150 plants are commercially grown for food production. 30 species provide 95% of human energy needs. As a matter of fact, the big four- rice, wheat, maize (corn), and potatoes account for more than 70% of human energy needs. There is so much pressure on a handful of crops to feed the world. Not only is the limited number of crop plants to feed the world a concern, but also the reduced genetic diversity that is found in these crops has been declining since 1900. FAO estimates place that 75% of the genetic diversity of our agricultural crops have been lost since 1900. Traditional crop varieties are being replaced with high yielding crops in the developing world where our major crops originated. The centers of crop origin were centers of great genetic diversity of our crops. As farmers abandon native low yielding crops for high yielding crops, the valuable genetic information stored in those native crops are often lost forever. These native plants may be low yielding with undesirable traits for quality and yield, but they were rich in valuable genes that could provide resistance to drought, disease, insects, etc. If we lose these valuable genes, we may lose the ability to grow our important crops in a world of constant change. It is a constant battle to stay one step ahead of pests and the changing environment.
Loss of genetic diversity for genetic uniformity is a recipe for disaster. There are a couple of examples in history where disaster occurred because of genetic uniformity or lack of genetic diversity. Examples of the importance of genetic diversity can be found in the Irish Potato Famine of the 1840’s and the Southern Corn Leaf Blight outbreak in the US in 1970.
The Spanish conquistadors brought the potato from its center of origin in present day Peru and Bolivia to Spain in 1565. In 1589, English explorer Sir Walter Raleigh, two years after his exploration of the US east coast from the Carolinas to Florida and one year after his help in defeating the “Invincible Spanish Armada” along the English coast in one of history’s great turning points, brought the potato to Ireland. In time, the Irish people relied heavily upon the potato for human and livestock food and feed. During the 1800’s, the Irish people relied heavily upon one variety of potato called the “Lumper.” All these potatoes that were planted at the time were clones of each other. A virulent race of the fungal pathogen Phytophthora Infestans, which causes late blight, started in Mexico in 1842 and reached the US east coast in 1843 and 1844 wiping out the American potato crop. The pathogen is believed to have hitched a ride on a ship that had late blight infected potatoes that were used to feed the passengers bound for Ireland in late 1844 to 1845. Once introduced to Ireland, the pathogen spread like wildfire across much of northern and central Europe. Since all the potatoes were identical with no resistance to this race of late blight, it spread at an alarming rate. Ireland bore the brunt of this disease as potato was the main source of food of the Irish people and cattle. From 1845-1849, over 1 million people died from starvation and disease and 1.5-2 million people left Ireland for North America and Australia. In just a few years, the island nation’s population dropped from 9 million down to 4 million people. This disaster not only changed the cultural and social structure of Europe, but it also forever changed society in the United States, Canada, and Australia.
The dangers of genetic uniformity and disease did not escape American agriculture in 1970. In 1970, almost 85% of US corn acres were planted to one type of corn called Texas cytoplasmic male sterile corn. This type of corn was highly susceptible to a new race of fungal pathogen that causes southern corn leaf blight. The combination of wet weather and a very susceptible host led to the rapid spread of this devastating pathogen. Yield losses were as high as 50-100% is some areas. Food energy losses were believed to be much greater than the losses incurred during the Irish Potato Famine and created more than $7 billion worth of damage (in 2020 dollars). Thankfully, the US had other sources of food and feed to bridge the gap unlike the Irish 120 years earlier. Resistance to this virulent fungus was found in an African maize variety called Mayorbella. A major catastrophe was averted by incorporating this resistance into the commercial corn varieties.
Today, with all the science and technology at our fingertips, we still are facing a barrage of challenges in keeping our crops healthy and productive for a hungry world. Tar spot in corn, Ug99 version of black stem rust in wheat, citrus greening in oranges, tropical race 4 or Panama disease in Cavendish bananas, and new races of Phytophthora Infestans in potatoes all threaten to reduce or wipe out these important crops worldwide. It is going to take a team of plant breeders, geneticists, agronomists, horticulturists, biologists, plant pathologists, etc. to keep ahead of this constant warfare. Facilities such as the US Potato Gene Bank in Sturgeon Bay will continue to play an important role in keeping our crops healthy for years to come.
Written By: Kevin Mueller, Senior Agronomist, WI CCA of the Year
Genetic diversity is very important in crops grown for food across the globe. According to the United Nations Food and Agriculture Organization (FAO), there are about 300,000 plant species that exist in the world today. 7000 plant species have been cultivated or collected for food at some point in the last couple of millennia. Today fewer than 150 plants are commercially grown for food production. 30 species provide 95% of human energy needs. As a matter of fact, the big four- rice, wheat, maize (corn), and potatoes account for more than 70% of human energy needs. There is so much pressure on a handful of crops to feed the world. Not only is the limited number of crop plants to feed the world a concern, but also the reduced genetic diversity that is found in these crops has been declining since 1900. FAO estimates place that 75% of the genetic diversity of our agricultural crops have been lost since 1900. Traditional crop varieties are being replaced with high yielding crops in the developing world where our major crops originated. The centers of crop origin were centers of great genetic diversity of our crops. As farmers abandon native low yielding crops for high yielding crops, the valuable genetic information stored in those native crops are often lost forever. These native plants may be low yielding with undesirable traits for quality and yield, but they were rich in valuable genes that could provide resistance to drought, disease, insects, etc. If we lose these valuable genes, we may lose the ability to grow our important crops in a world of constant change. It is a constant battle to stay one step ahead of pests and the changing environment.
Loss of genetic diversity for genetic uniformity is a recipe for disaster. There are a couple of examples in history where disaster occurred because of genetic uniformity or lack of genetic diversity. Examples of the importance of genetic diversity can be found in the Irish Potato Famine of the 1840’s and the Southern Corn Leaf Blight outbreak in the US in 1970.
The Spanish conquistadors brought the potato from its center of origin in present day Peru and Bolivia to Spain in 1565. In 1589, English explorer Sir Walter Raleigh, two years after his exploration of the US east coast from the Carolinas to Florida and one year after his help in defeating the “Invincible Spanish Armada” along the English coast in one of history’s great turning points, brought the potato to Ireland. In time, the Irish people relied heavily upon the potato for human and livestock food and feed. During the 1800’s, the Irish people relied heavily upon one variety of potato called the “Lumper.” All these potatoes that were planted at the time were clones of each other. A virulent race of the fungal pathogen Phytophthora Infestans, which causes late blight, started in Mexico in 1842 and reached the US east coast in 1843 and 1844 wiping out the American potato crop. The pathogen is believed to have hitched a ride on a ship that had late blight infected potatoes that were used to feed the passengers bound for Ireland in late 1844 to 1845. Once introduced to Ireland, the pathogen spread like wildfire across much of northern and central Europe. Since all the potatoes were identical with no resistance to this race of late blight, it spread at an alarming rate. Ireland bore the brunt of this disease as potato was the main source of food of the Irish people and cattle. From 1845-1849, over 1 million people died from starvation and disease and 1.5-2 million people left Ireland for North America and Australia. In just a few years, the island nation’s population dropped from 9 million down to 4 million people. This disaster not only changed the cultural and social structure of Europe, but it also forever changed society in the United States, Canada, and Australia.
The dangers of genetic uniformity and disease did not escape American agriculture in 1970. In 1970, almost 85% of US corn acres were planted to one type of corn called Texas cytoplasmic male sterile corn. This type of corn was highly susceptible to a new race of fungal pathogen that causes southern corn leaf blight. The combination of wet weather and a very susceptible host led to the rapid spread of this devastating pathogen. Yield losses were as high as 50-100% is some areas. Food energy losses were believed to be much greater than the losses incurred during the Irish Potato Famine and created more than $7 billion worth of damage (in 2020 dollars). Thankfully, the US had other sources of food and feed to bridge the gap unlike the Irish 120 years earlier. Resistance to this virulent fungus was found in an African maize variety called Mayorbella. A major catastrophe was averted by incorporating this resistance into the commercial corn varieties.
Today, with all the science and technology at our fingertips, we still are facing a barrage of challenges in keeping our crops healthy and productive for a hungry world. Tar spot in corn, Ug99 version of black stem rust in wheat, citrus greening in oranges, tropical race 4 or Panama disease in Cavendish bananas, and new races of Phytophthora Infestans in potatoes all threaten to reduce or wipe out these important crops worldwide. It is going to take a team of plant breeders, geneticists, agronomists, horticulturists, biologists, plant pathologists, etc. to keep ahead of this constant warfare. Facilities such as the US Potato Gene Bank in Sturgeon Bay will continue to play an important role in keeping our crops healthy for years to come.
Written By: Kevin Mueller, Senior Agronomist, WI CCA of the Year