Crop Diversity - Disease Threats To Crops With Low Genetic Diversity

Disease Threats To Crops With Low Genetic Diversity

One particular threat to mass-producing plants for harvest is their susceptibility to diseases. Generally speaking, a species has a range of genetic variability that allows for individuals and/or populations within that species to survive should a stressor or disturbance occur. In the case of agriculture, this is a tricky business to ensure, as seeds are planted under uniform conditions. For example, monocultural agriculture potentially elicits low crop diversity (especially if the seeds were mass-produced or cloned). It is possible that a single pest or disease could wipe out entire areas of a crop due to this uniformity. One of the more historically known examples of harvests that suffered from low crop diversity was the Irish Potato Famine of 1845-1847.

One growing danger to present day agriculture is something called wheat rust: the name given from the reddish spores, it is a fungus that attaches to plants and breaks them down for food. A new form of the wheat disease - stem rust, strain Ug99 - has spread from Africa across to the Arabian Peninsula. This development was summarized on the January 16th 2007 by the international research centers Borlaug Global Rust Initiative and the Agricultural Research Service of the United States Department of Agriculture over 2 years of observation after its initial outbreak. The Ug99 stem rust has recently proven to be even more virulent than other forms. Observations from field trials in Kenya showed that more than 85% of wheat samples, including cultivars from the major wheat producing regions in the world, have succumbed to the pest. This is a serious pest alert for one of the major food crops of the world. The key to overcome the threat is genetic resistance found in certain wheat varieties. As Nobel laureate Norman Borlaug puts it: “We know what to do and how to do it. All we need are the financial resources, scientific cooperation and political will to contain this threat to world food security.”

Reports from Burundi and Angola warn of another looming food crisis partly caused by outbreaks of the African Cassava Mosaic Virus (ACMD). Creating a “mosaic” of decay on the plants leaves, ACMD is responsible for the loss of a million tons of food each year. The Famine Early Warning Network of USAID reports from Angola that pockets of food insecurity exist in a number of districts partly due to the impacts of mosaic virus on the cassava crop. Likewise FAO (Food and Agriculture Organization of the United Nations) has warned about food insecurity in north and east central Burundi and one of the factors causing the precarious situation is declining yam harvests and the losses of cassava crops to the mosaic virus. CMD also affects people already exposed to malnutrition and with limited coping mechanisms. CMD continues to be prevalent in all the main cassava-growing areas in the Great Lakes region of east Africa, causing between 20 and 90 percent crop losses in the Congo. Breeders and relief agencies work together to fight the disease, and the FAO emergency relief and rehabilitation program is engaged in a project to assist vulnerable returnee populations in the African Great Lakes Region through mass propagation and distribution of CMD resistant or highly tolerant cassava planting materials.

A well known occurrence of disease susceptibility in crops lacking diversity concerns the Gros Michel, a seedless banana that saw world marketing in the 1940s. As the market demand became high for this particular species, growers and farmers of the Gros Michel banana began to use this species almost exclusively. Genetically, these bananas are duplicates of every other in their species due to its self-pollinating reproductive style, and because of this lack of genetic diversity, are now virtually extinct due to a single fungus; Panama Disease. This fungus (also known as Fusarium wilt), which infected Gros Michel banana crops in the 1950s, completely wiped out the Gros Michel as the predecessor to the current, and most popular, banana on the market: the Cavendish.