Crop diversity

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Crop diversity or crop biodiversity is the variety and variability of crops, plants used in agriculture, including their genetic and phenotypic characteristics. It is a subset of and a specific element of agricultural biodiversity. Over the past 50 years, there has been a major decline in two components of crop diversity; genetic diversity within each crop and the number of species commonly grown.

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Crop diversity loss threatens global food security, as the world's human population depends on a diminishing number of varieties of a diminishing number of crop species. Crops are increasingly grown in monoculture, meaning that if, as in the historic Great Famine of Ireland, a single disease overcomes a variety's resistance, it may destroy an entire harvest, or as in the case of the 'Gros Michel' banana, may cause the commercial extinction of an entire variety. With the help of seed banks, international organizations are working to preserve crop diversity.

Biodiversity loss

Geographic hotspots of distributions of crop wild relatives not represented in genebanks Geographic hotspots of distributions of crop wild relatives not represented in genebanks.tif
Geographic hotspots of distributions of crop wild relatives not represented in genebanks

The loss of biodiversity is considered one of today’s most serious environmental concerns by the Food and Agriculture Organization. [1] [2] If current trends persist, as many as half of all plant species could face extinction. [3] Some 6% of wild relatives of cereal crops such as wheat, maize, rice, and sorghum are under threat, as are 18% of legumes (Fabaceae), the wild relatives of beans, peas and lentils, and 13% of species within the botanical family (Solanaceae) that includes potato, tomato, eggplant (aubergine), and peppers (Capsicum). [4]

Within-crop diversity

Within-crop diversity, a specific crop can result from various growing conditions, for example a crop growing in nutrient-poor soil is likely to have stunted growth than a crop growing in more fertile soil. The availability of water, soil pH level, and temperature similarly influence crop growth. [5]

Within-crop diversity: maize cobs of differing colours Corncobs edit1.jpg
Within-crop diversity: maize cobs of differing colours

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. [5] Such traits collectively determine a crop's overall characteristics and their future potential. 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.

Traditional mixed crop (polyculture) cultivation of cacao and banana, Trinidad, 1903 Fotg cocoa d066 trinidadian mixed crop cultivation of cacao.png
Traditional mixed crop (polyculture) cultivation of cacao and banana, Trinidad, 1903

Modern plant breeders develop new crop varieties to meet specific conditions. A new variety might, for example, be higher yielding, more disease resistant or have a longer shelf life than the varieties from which it was bred. The practical use of crop diversity goes back to early agricultural methods of crop rotation and fallow fields, where planting and harvesting one type of crop on a plot of land one year, and planting a different crop on that same plot the next year. This takes advantage of differences in a plant's nutrient needs, but more importantly reduces the buildup of pathogens. [6]

Both farmers and scientists must continually draw on the irreplaceable resource of genetic diversity to ensure productive harvests. 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. [7] The breeding of high performing crops steadily reduces genetic diversity as desirable traits are selected, and undesirable traits are removed. Farmers can increase within-crop diversity to some extent by planting mixtures of crop varieties. [8]

Ecological effects

Biodiverse agroecosystem: traditional potato harvesting high in the Andes, Manco Kapac Province, Bolivia, 2012 Ch'uqi palliwi.JPG
Biodiverse agroecosystem: traditional potato harvesting high in the Andes, Manco Kapac Province, Bolivia, 2012

Agricultural ecosystems function effectively as self-regulating systems provided they have sufficient biodiversity of plants and animals. Apart from producing food, fuel, and fibre, agroecosystem functions include recycling nutrients, maintaining soil fertility, regulating microclimate, regulating water flow, controlling pests, and detoxification of waste products. [5]

However, modern agriculture seriously reduces biodiversity. Traditional systems maintain diversity within a crop species, such as in the Andes mountains where up to 50 varieties of potato are grown. [5] Strategies to raise genetic diversity can involve planting mixtures of crop varieties. [5]

Genetic diversity of crops can be used to help protect the environment. Crop varieties that are resistant to pests and diseases can reduce the need for application of harmful pesticides. [7]

Economic impact

Agriculture is the economic foundation of most countries, and for developing countries a likely source of economic growth. Growth in agriculture can benefit the rural poor, though it does not always do so. Profits from crops can increase from higher value crops, better marketing, value-adding activities such as processing, or expanded access for the public to markets. [9]  Profits can also decrease through reduced demand or increased production. Crop diversity can protect against  crop failure, and can also offer higher returns. [10] [11]

Despite efforts to quantify them, the financial values of crop diversity sources remain entirely uncertain. [12]

Disease threats

Loss of low-diversity crop to a single disease: the Great Famine, caused by the oomycete Phytophthora infestans. Starvation followed, as illustrated by James Mahony, 1847 Skibbereen by James Mahony, 1847.JPG
Loss of low-diversity crop to a single disease: the Great Famine, caused by the oomycete Phytophthora infestans . Starvation followed, as illustrated by James Mahony, 1847
Wheat stem rust is evolving new, virulent strains, threatening many low-diversity cultivars. Stem rust close up.jpg
Wheat stem rust is evolving new, virulent strains, threatening many low-diversity cultivars.

Along with insect pests, disease is a major cause of crop loss. [13] Wild species have a range of genetic variability that allows some individuals to survive should a disturbance occur. In agriculture, resistance through variability is compromised, since genetically uniform seeds are planted under uniform conditions. Monocultural agriculture thus causes low crop diversity, especially when the seeds are mass-produced or when plants (such as grafted fruit trees and banana plants) are cloned. A single pest or disease could threaten a whole crop due to this uniformity ("genetic erosion"). [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. Another example is when a disease caused by a fungus affected the monocultured 1970 US corn crop, causing a loss of over one billion dollars in production. [15]

A danger to agriculture is wheat rust, a pathogenic fungus causing reddish patches, coloured by its spores. A virulent form of the wheat disease, stem rust, strain Ug99, spread from Africa across to the Arabian Peninsula by 2007. [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. The Nobel laureate Norman Borlaug argued for action to ensure global food security. [17]

Low-diversity crop variety destroyed: the 'Gros Michel' banana was commercially destroyed by Panama disease, caused by the fungus Fusarium oxysporum (illustrated). K7725-1-sm.jpg
Low-diversity crop variety destroyed: the 'Gros Michel' banana was commercially destroyed by Panama disease, caused by the fungus Fusarium oxysporum (illustrated).

Reports from Burundi and Angola warn of a threat to food security caused by the African Cassava Mosaic Virus (ACMD). [18] ACMD is responsible for the loss of a million tons of cassava each year. [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. [21]

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 cultivar, growers and farmers began to use the Gros Michel banana almost exclusively. Genetically, these bananas are clones, and because of this lack of genetic diversity, are all susceptible to a single fungus, Fusarium oxysporum (Panama disease); large areas of the crop were destroyed by the fungus in the 1950s. [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'. [23]

Such threats can be countered by strategies such as planting multi-line cultivars and cultivar mixes, in the hope that some of the cultivars will be resistant to any individual outbreak of disease. [24]

Organizations and technologies

The implications of crop diversity are at both local and world levels. Global organizations that aim to support diversity include Bioversity International (formerly known as International Plant Genetic Resources Institute), the International Institute of Tropical Agriculture, the Borlaug Global Rust Initiative, and the International Network for Improvement of Banana and Plantain. 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. [1] One such step taken in the action against the loss of biodiversity among crops is gene banking. 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.

Six bean varieties at a gene bank Six bean varieties at a gene bank.jpg
Six bean varieties at a gene bank

The Global Crop Diversity Trust is an independent international organisation which exists to ensure the conservation and availability of crop diversity for food security worldwide. It was established through a partnership between the United Nations Food and Agriculture Organization (FAO) and CGIAR acting through Bioversity International. [25] The CGIAR is a consortium of international agriculture research centers (IARC) and others that each conduct research on and preserve germplasm from a particular crop or animal species. The genebanks of CGIAR centers hold some of the world's largest off site collections of plant genetic resources in trust for the world community. Collectively, the CGIAR genebanks contain more than 778,000 accessions of more than 3,000 crop, forage, and agroforestry species. [26] The collection includes farmers' varieties and improved varieties and, in substantial measure, the wild species from which those varieties were created. [3] National germplasm storage centers include the U.S. Department of Agriculture's National Center for Genetic Resources Preservation, India's National Bureau of Animal Genetic Resources, the Taiwan Livestock Research Institute, and the proposed Australian Network of Plant Genetic Resource Centers. [27] [28] [29] [30]

Plants in the International Center for Tropical Agriculture's gene bank, Colombia Genebank4 (4331057760).jpg
Plants in the International Center for Tropical Agriculture's gene bank, Colombia

The World Resources Institute (WRI) and the World Conservation Union (IUCN) are non-profit organizations that provide funding and other support to off site and on site conservation efforts. The wise use of crop genetic diversity in plant breeding and genetic modification can also contribute significantly to protecting the biodiversity in crops. Crop varieties can be genetically modified to resist specific pests and diseases. For example, a gene from the soil bacterium Bacillus thuringiensis (Bt) produces a natural insecticide toxin. 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. [31]

See also

Notes

    Related Research Articles

    <span class="mw-page-title-main">Monoculture</span> Farms producing only one crop at a time

    In agriculture, monoculture is the practice of growing one crop species in a field at a time. Monoculture is widely used in intensive farming and in organic farming: both a 1,000-hectare cornfield and a 10-ha field of organic kale are monocultures. Monoculture of crops has allowed farmers to increase efficiency in planting, managing, and harvesting, mainly by facilitating the use of machinery in these operations, but monocultures can also increase the risk of diseases or pest outbreaks. This practice is particularly common in industrialized nations worldwide. Diversity can be added both in time, as with a crop rotation or sequence, or in space, with a polyculture or intercropping.

    <span class="mw-page-title-main">Seed bank</span> Backup seed storage

    A seed bank stores seeds to preserve genetic diversity; hence it is a type of gene bank. There are many reasons to store seeds. One is to preserve the genes that plant breeders need to increase yield, disease resistance, drought tolerance, nutritional quality, taste, etc. of crops. Another is to forestall loss of genetic diversity in rare or imperiled plant species in an effort to conserve biodiversity ex situ. Many plants that were used centuries ago by humans are used less frequently now; seed banks offer a way to preserve that historical and cultural value. Collections of seeds stored at constant low temperature and low moisture are guarded against loss of genetic resources that are otherwise maintained in situ or in field collections. These alternative "living" collections can be damaged by natural disasters, outbreaks of disease, or war. Seed banks are considered seed libraries, containing valuable information about evolved strategies to combat plant stress, and can be used to create genetically modified versions of existing seeds. The work of seed banks often span decades and even centuries. Most seed banks are publicly funded and seeds are usually available for research that benefits the public.

    The International Treaty on Plant Genetic Resources for Food and Agriculture, is a comprehensive international agreement in harmony with the Convention on Biological Diversity, which aims at guaranteeing food security through the conservation, exchange and sustainable use of the world's plant genetic resources for food and agriculture (PGRFA), the fair and equitable benefit sharing arising from its use, as well as the recognition of farmers' rights. It was signed in 2001 in Madrid, and entered into force on 29 June 2004.

    <span class="mw-page-title-main">CGIAR</span> Food security research organisation

    CGIAR is a global partnership that unites international organizations engaged in research about food security. CGIAR research aims to reduce rural poverty, increase food security, improve human health and nutrition, and sustainable management of natural resources.

    <span class="mw-page-title-main">Agricultural biodiversity</span> Agricultural concept

    Agricultural biodiversity or agrobiodiversity is a subset of general biodiversity pertaining to agriculture. It can be defined as "the variety and variability of animals, plants and micro-organisms at the genetic, species and ecosystem levels that sustain the ecosystem structures, functions and processes in and around production systems, and that provide food and non-food agricultural products.” It is managed by farmers, pastoralists, fishers and forest dwellers, agrobiodiversity provides stability, adaptability and resilience and constitutes a key element of the livelihood strategies of rural communities throughout the world. Agrobiodiversity is central to sustainable food systems and sustainable diets. The use of agricultural biodiversity can contribute to food security, nutrition security, and livelihood security, and it is critical for climate adaptation and climate mitigation.

    <span class="mw-page-title-main">Seed saving</span> Practice of saving plant reproductive material

    In agriculture and gardening, seed saving is the practice of saving seeds or other reproductive material from vegetables, grain, herbs, and flowers for use from year to year for annuals and nuts, tree fruits, and berries for perennials and trees. This is the traditional way farms and gardens were maintained for the last 12,000 years.

    <span class="mw-page-title-main">Germplasm</span>

    Germplasm are genetic resources such as seeds, tissues, and DNA sequences that are maintained for the purpose of animal and plant breeding, conservation efforts, agriculture, and other research uses. These resources may take the form of seed collections stored in seed banks, trees growing in nurseries, animal breeding lines maintained in animal breeding programs or gene banks. Germplasm collections can range from collections of wild species to elite, domesticated breeding lines that have undergone extensive human selection. Germplasm collection is important for the maintenance of biological diversity, food security, and conservation efforts.

    <span class="mw-page-title-main">Heirloom plant</span> Historic food crop cultivar

    An heirloom plant, heirloom variety, heritage fruit, or heirloom vegetable is an old cultivar of a plant used for food that is grown and maintained by gardeners and farmers, particularly in isolated communities of the Western world. These were commonly grown during earlier periods in human history, but are not used in modern large-scale agriculture.

    <span class="mw-page-title-main">Svalbard Global Seed Vault</span> Globally accessible seed bank on Spitsbergen, Svalbard, Norway

    The Svalbard Global Seed Vault is a secure backup facility for the world's crop diversity on the Norwegian island of Spitsbergen in the remote Arctic Svalbard archipelago. The Seed Vault provides long-term storage of duplicates of seeds conserved in genebanks around the world. This provides security of the world's food supply against the loss of seeds in genebanks due to mismanagement, accident, equipment failures, funding cuts, war, sabotage, disease and natural disasters. The Seed Vault is managed under terms spelled out in a tripartite agreement among the Norwegian government, the Crop Trust, and the Nordic Genetic Resource Center (NordGen).

    <span class="mw-page-title-main">Gene bank</span> Facility that preserves genetic material

    Gene banks are a type of biorepository that preserves genetic material. For plants, this is done by in vitro storage, freezing cuttings from the plant, or stocking the seeds. For animals, this is done by the freezing of sperm and eggs in zoological freezers until further need. With corals, fragments are taken and stored in water tanks under controlled conditions. Genetic material in a 'gene bank' is preserved in a variety of ways, such as freezing at -196 °C in liquid nitrogen, being placed in artificial ecosystems, or put in controlled nutrient media.

    Food biodiversity is defined as "the diversity of plants, animals and other organisms used for food, covering the genetic resources within species, between species and provided by ecosystems."

    <span class="mw-page-title-main">Crop Trust</span>

    The Crop Trust, officially known as the Global Crop Diversity Trust, is an international nonprofit organization with a secretariat in Bonn, Germany. Its mission is to conserve and make available the world's crop diversity for food security.

    <span class="mw-page-title-main">Bioversity International</span>

    Bioversity International is a global research-for-development organization that delivers scientific evidence, management practices and policy options to use and safeguard agricultural biodiversity to attain global food- and nutrition security, working with partners in low-income countries in different regions where agricultural biodiversity can contribute to improved nutrition, resilience, productivity and climate change adaptation.

    <span class="mw-page-title-main">Crop wild relative</span> Wild plant closely related to a domesticated plant

    A crop wild relative (CWR) is a wild plant closely related to a domesticated plant. It may be a wild ancestor of the domesticated (cultivated) plant or another closely related taxon.

    Forest genetic resources or foresttree genetic resources are genetic resources of forest shrub and tree species. Forest genetic resources are essential for forest-depending communities who rely for a substantial part of their livelihoods on timber and non-timber forest products for food security, domestic use and income generation. These resources are also the basis for large-scale wood production in planted forests to satisfy the worldwide need for timber and paper. Genetic resources of several important timber, fruit and other non-timber tree species are conserved ex situ in genebanks or maintained in field collections. Nevertheless, in situ conservation in forests and on farms is in the case of most tree species the most important measure to protect their genetic resources.

    The World Vegetable Center (WorldVeg), previously known as the Asian Vegetable Research and Development Center (AVRDC), is an international, nonprofit institute for vegetable research and development. It was founded in 1971 in Shanhua, southern Taiwan, by the Asian Development Bank, Taiwan, South Korea, Japan, the Philippines, Thailand, the United States and South Vietnam.

    Genesys is an online, global portal about plant genetic resources for food and agriculture. It is a gateway from which germplasm accessions from gene banks around the world can be easily found and ordered.

    The Seed Savers' Network (SSN) is an Australian not-for-profit organisation, based in Byron Bay, New South Wales. Since 1986, SSN has organised gardeners and farmers to collect, multiply and redistribute garden seeds in Australia and also within peasant organisations worldwide.

    The National Centre for Plant Genetic Resources: Polish Genebank (NCPGR) is a research unit in the Plant Breeding and Acclimatization Institute – National Research Institute. NCPGR is the coordinator and implementer of the National Crop Plant Genetic Resources Protection Programme. The Programme aims to protect the biodiversity of crop plants endangered by genetic erosion in Poland, and is funded by the Ministry of Agriculture. The main tasks include collection of crop and wild plant populations and varieties threatened by genetic erosion, description and evaluation of collected materials, and preservation of their viability and genetic purity. The Programme is an implementation of provisions laid down in international treaties ratified by Poland:

    <span class="mw-page-title-main">Plant genetic resources</span>

    Plant genetic resources describe the variability within plants that comes from human and natural selection over millennia. Their intrinsic value mainly concerns agricultural crops.

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    Further reading