Crop diversity

[5] In addition, diversity of a harvested plant can be the result of genetic differences: a crop may have genes conferring early maturity or disease resistance.

Diversity within a crop includes genetically-influenced attributes such as seed size, branching pattern, height, flower color, fruiting time, and flavor.

Crops can also vary in less obvious characteristics such as their response to heat, cold, a drought, or their ability to resist specific diseases and pests.

While genetic variability provides farmers with plants that have a higher resilience to pests and diseases and allows scientists access to a more diverse genome than can be found in highly selected crops.

[14] A well-known historic case was the Great Famine of Ireland of 1845-1847, where a vital crop with low diversity was destroyed by a single fungus.

[16] In field trials in Kenya, more than 85% of wheat samples, including major cultivars, were susceptible,[16] implying that higher crop diversity was required.

[17] Reports from Burundi and Angola warn of a threat to food security caused by the African Cassava Mosaic Virus (ACMD).

[19] CMD is 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.

[20] The FAO emergency relief and rehabilitation program is assisting vulnerable returnee populations in the African Great Lakes Region through mass propagation and distribution of CMD resistant or highly tolerant cassava.

[22] 'Gros Michel' has been replaced by the current main banana on the market, the 'Cavendish', which in turn is (2015) at risk of total loss to a strain of the same fungus, 'Tropical Race 4'.

Members of the United Nations, at the World Summit on Sustainable Development 2002 at Johannesburg, said that crop diversity is in danger of being lost if measures are not taken.

There are a number of organizations that enlist teams of local farmers to grow native varieties, particularly those that are threatened by extinction due to lack of modern-day use.

There are also local, national and international efforts to preserve agricultural genetic resources through off-site methods such as seed and banks for further research and crop breeding.

Genes from Bt can be inserted into crop plants to make them capable of producing an insecticidal toxin and therefore a resistance to certain pests.

Bt corn (maize) can however adversely affect non-target insects closely related to the target pest, as with the monarch butterfly.