In this article we will discuss about:- 1. Meaning of Genetic Erosion 2. Causes of Genetic Erosion 3. Prevention.
Meaning of Genetic Erosion:
Genetic erosion refers to the gradual reduction in genetic variability, in the population of a species, due to elimination of various genotypes. In other words, the loss of genetic diversity caused by either natural or man-made processes is referred to as genetic erosion. Thus, genetic erosion is more in endangered species.
Genetic erosion in crop biodiversity is the loss of genetic diversity, including the loss of individual genes, and the loss of particular combination of genes (or gene complexes) such as those manifested in locally adapted landraces of domesticated plants adapted to the natural environment in which they originated.
The term genetic erosion is sometimes used in a narrow sense, such as for the loss of alleles or genes, as well as more broadly, referring to the loss of varieties or even species. The major driving forces behind genetic erosion in crops are: variety replacement, land cleaning, over exploitation of species, population pressure, environmental degradation, overgrazing, policy and changing agricultural systems.
Causes of Genetic Erosion:
Genetic erosion occurs because each individual genotype has many unique genes which get lost when it dies without reproduction. Low genetic diversity in wild species of plants leads to a further reduction in the gene pool. Inbreeding and a weakening of immune system lead to eventual extinction of a species.
There are five main reasons of genetic erosion, viz.:
(i) Replacement of land races by modern cultivars,
(ii) Industrial agriculture,
(iii) Farming into wild habitat,
(iv) Clean cultivation, and
(v) Developmental activities.
These are briefly discussed below:
(i) Replacement of Land Races by Modern Cultivars:
The main factor for genetic erosion is the replacement of local varieties of domestic plants by high yielding or exotic varieties or species. A large number of varieties can also often be dramatically reduced when commercial varieties (including GMOs) are introduced into traditional farming systems. Many researchers believe that the main problem related to agro-ecosystem management is the general tendency towards genetic and ecological uniformity imposed by the development of modern agriculture.
Land races are primitive cultivars which are being grown by farmer’s generation after generation. Land race have genetic diversity, wider adaptability, broad genetic base and high degree of resistance to biotic and abiotic stresses. On the other hand, modern cultivars are high yielding but have narrow genetic base as they do not have genetic variability and are highly uniform.
According to the Food and Agriculture Organization of the United Nations, 75 per cent of crop diversity was lost during the twentieth century. Modern varieties have supplanted traditional varieties for 70 per cent of the word’s corn, 75 per cent of Asian rice, and half of the wheat in Africa, Latin America, and Asia. In 1950, India had 30,000 wild varieties of rice, but by 2015 only 50 are expected to remain. New, uniform plant varieties are replacing farmer’s traditional varieties and the traditional ones are becoming extinct.
(ii) Industrial Agriculture:
It requires genetic uniformity. Vast areas are typically planted to a single, high-yielding variety or a handful of genetically similar cultivars using capital intensive inputs like irrigation, fertilizer and pesticides to maximize production. A uniform crop is a breeding ground for disaster because it is more vulnerable to epidemics of pests and diseases.
Mechanization requires farms to have uniform crop types, structures, and management practices (for example, planting and harvesting dates). As a result, crop diversity has declined on most farms over the last century. For example, traditional farms, especially in the tropics, may include grains, root crops, vegetables, spices, medicinal plants; and trees for timber, fruit, and firewood.
In contrast, most modem farms have monocultures — that is, they have only one crop species planted over a large area. Farms with low crop diversity have poor “associated diversity” of species that were not assembled directly, such as insects, birds, and soil organisms.
(iii) Farming into Wild Habitat:
The maximum genetic diversity of all agricultural crops lies within the centres of genetic diversity where crops were first domesticated. In these regions wild relatives of crop species grow amongst farmer’s fields and in the margins of fields and there is a constant recycling of genes. These regions are under threat from the introduction of modern agricultural practices and population pressure in many countries.
(iv) Clean Cultivation:
The modernization of agriculture and clean cultivation, have resulted in elimination of wild and weedy forms of many crops leading to reduction in genetic diversity. The exchange of, genes between cultivated and wild species enhance the genetic variability in a population.
(v) Developmental Activities:
Various developmental activities such as development of national highways, towns, cities, airports, seaports have resulted in the elimination of many valuable wild and weedy forms of cultivated species.
Prevention of Genetic Erosion:
The entire world’s endangered plant species are plagued by varying degrees of genetic erosion and most of them need a human intervention to keep their population viable and to save them from extinction.
Genetic erosion gets compounded and accelerated by habitat fragmentation. Today most endangered species live in smaller and smaller chunks of fragmented habitat interspersed with human settlements and farmland making it impossible for them to naturally meet and breed with others of their kind, many die off without getting a fair chance to breed and pass on their genes in the living population.
The loss of biodiversity poses a serious threat to agriculture and the livelihoods of millions of people. Conserving biodiversity and using it wisely is a global necessity. Biodiversity provides the foundation for our agricultural systems. It provides the sources of traits to improve yield, quality, resistance to pests and diseases and adaptation to changing environmental conditions, such as global warming.
The protection of plant diversity is essential for food security and ecological well-being. Biodiversity is also a direct source of food for many people and is an essential part of our life support system. Without biodiversity, our ecosystems and the planet’s entire biosphere cannot function.
Conservation refers to protection of genetic diversity of crop plants from genetic erosion.
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