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crop diversity
Crop diversity is the variance in genetic and phenotypic characteristics of plants used in agriculture. Crops may vary in seed size, branching pattern, in height, flower color, fruiting time, or flavor. They may also vary in less obvious characteristics such as their response to heat, cold or drought, or their ability to resist specific diseases and pests. It is possible to discover variation in almost every conceivable trait, including nutritional qualities, preparation and cooking techniques, and of course how a crop tastes. And if a trait cannot be found in the crop itself, it can often be found in a wild relative of the crop; a plant that has similar species that have not been farmed or used in agriculture, but exist in the wild.〔Crop Wild Relatives “Global Portal.” Bioversity International, Dec 5 2008〕
Diversity in a crop can also result from different growing conditions: a crop growing in nutrient poor soil is likely to be shorter than a crop growing in more fertile soil. In addition, and perhaps most importantly, diversity of a harvested plant can be the result of genetic differences: a crop may have genes conferring early maturity or disease resistance.〔Imbruce, Valerie. “Bringing Southeast Asia to the Southeast United States: New forms of alternative agriculture in Homestead, Florida.” Agriculture and Human Values Vol. 24, no. 1, pp. 41–59. Mar 2007〕 It is these heritable traits that are of special interest as they are passed on from generation to generation and collectively determine a crop’s overall characteristics and future potential. Through combining genes for different traits in desired combinations, plant breeders are able to develop new crop varieties to meet specific conditions. A new variety might, for example, be higher yielding, more disease resistant and 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, planting and harvesting one type of crop on a plot of land one year, and using a different crop the next based on differences in a plant's nutrient needs. Both farmers and scientists must continually draw on the irreplaceable resource of genetic diversity to ensure productive harvests, as genetic variability provides farmers resilience to pests and diseases and allows scientists access to a more diverse genetic bank. Diversification of harvests and maintaining wild biodiversity in crop relatives influence many aspects of human and global interaction, being important for environmental and species sustainability.〔Jarvis, Devra I. and Camplain, Dindo M. “Crop genetic diversity to reduce pests and diseases on-farm: Participatory diagnosis guidelines Version I.” BioversityTechnical Bulletin No. 12, Bioversity International. October 2004〕
== Benefits to the environment ==
The loss of biodiversity is considered one of today’s most serious environmental concerns by the Food and Agriculture Organization of the United Nations.〔United Nations. World Summit on Sustainable Development. August 29, 2002〕 According to some estimates, if current trends persist, as many as half of all plant species could face extinction.〔Associated Press. “Threat seen to half of Earth's plant species.” The Milwaukee Journal Sentinel (Milwaukee, WI). November 1, 2002〕 Among the many threatened species are wild relatives of our crops – species that could contribute invaluable traits to future crop varieties. It has been estimated that 6% of wild relatives of cereal crops (wheat, maize, rice, sorghum etc.) are under threat as are 18% of legume species (the wild relatives of beans, peas and lentils) and 13% of species within the botanical family that includes potato, tomato, eggplant, and pepper.〔Crop Wild Relatives “Global Portal.” Bioversity International, Dec 5 200〕 Some recent research, however, questions the crop diversity erosion thesis with data drawn from commercially available vegetable and apple varieties.
The wise use of crop genetic diversity in plant breeding can contribute significantly to protecting the environment. Crop varieties that are resistant to pests and diseases can reduce the need for application of harmful pesticides more vigorous varieties can better compete with weeds;〔Kropff, M.J. “Project: Enhanced biodiversity and weed suppression in agro-ecosystems.” Crop and Weed Ecology Group (WUR), METIS Wageningen University (2001-2005)〕 reducing the need for applying herbicides as in the case study at Aarhus University in Denmark using more robust maize;〔Melander, Bo. “Maize cropping with less herbicide.” Integrated Weed Management, Case study 1. ENDURE, September 2008〕 drought resistant plants can help save water through reducing the need for irrigation;〔Nautiyal, S; Kaechele, H. “Conservation of crop diversity for sustainable landscape development.” Management of Environmental Quality. Vol. 18, no. 5, pp. 514–530. 2007〕 deeper rooting varieties can help stabilize soils; and varieties that are more efficient in their use of nutrients require less fertilizer.〔Smith, Linda. “GMOs – A Crop Technology Whose Time Has Come.” Fleishman and Hillard. June 11, 2008〕 Most importantly, perhaps, productive agricultural systems reduce or eliminate the need to cut down forest or clear fragile lands to create more farmland for food production.
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