Usefulness of and Threats to Plant Genetic Resources

2.1 Biodiversity and Plant Genetic Resources

For millennia, living species have been evolving, dispersing, and scattering beyond their native areas. Confronted with various habitats, they gradually adapted to their new environment and climate under constraints, natural and manmade, that created very broad genetic diversity within each species. This forms what we call today PGR. The PGRs of particular importance to humans are those that comprise food and agriculture, including the diversity of genetic material contained in traditional seed varieties and modern cultivars, as well as wild plant species that can be used as food, feed for animals, fiber, shelter, energy, etc. Until now, this broad diversity was considered a free and available commodity available for common use.

In 1995 it was estimated that among the 250,000 species of higher plants identified, about 30,000 are edible and about 7,000 plant species have been used as food in agriculture. Thus, several thousand species with extensive diversity are considered to contribute to food (Wilson 1992). Cultivated PGRs are classified into three broad categories, namely “modern varieties,” “farmers' varieties,” and “landraces and wild relatives' species.”¹

• Modern Varieties (sometimes called high-yielding varieties) are the products of plant breeding in the formal system. They typically have a high degree of genetic uniformity.
• Farmers' varieties, otherwise known as traditional varieties, are the product of breeding or selection carried out by farmers, either deliberately or not, continuously over many generations. Farmers' varieties tend not to be genetically uniform² and contain high levels of genetic diversity (Tomooka 1991; Ceccarelli et al. 1992; Alika, Aken'Ova, and Fatoukan 1993).
• Landraces and wild relatives, however, can be recognized morphologically. Farmers have names for them and different landraces differ in adaptation to soil type, time of seeding, date of maturity, height, nutritive value, use as well as in hue, taste, nutrition, preservability, medicinal quality, pest, drought and flood resistance (Harlan 1975).

2.2 The Value of Genetic Resources and Genetic Diversity to Smallholder Farmers

Farmers in fertile and/or irrigated areas who can afford to invest in appropriate improved crop varieties and external inputs are usually rewarded with increased yield and income. The majority of farmers in developing countries however, particularly poor farmers in rain-fed ecosystems, cannot afford expensive external inputs such as fertilizers, pesticides or seeds adapted and improved for profitability. So it is thanks to the genetic diversity of traditional plants—both at intra and interspecific levels—that are well adapted to locally poor conditions that such farmers continue to survive.

The majority of poor farmers live in arid zones with low soil fertility and unpredictable conditions, such as poor or erratic rainfall, very long or short growing seasons, and lack of external inputs. In such environments, it is the local varieties and landraces which provide smallholder farmers with a more reliable crop yield.

2.3 Contribution of Plant Genetic Resource Diversity to Modern Varieties

PGR diversity represents a vast genetic "library" from which we can obtain many useful genes. Each variety of plants possesses value to humankind that remains undiscovered, so PGR diversity represents a true “resource” which humankind can continue to turn to for agriculture, food, medicine, industry and other future uses.

Specific genes or gene combinations provide valuable benefits including agronomic qualities such as resistance to pests, diseases, and drought; adaptations to abiotic stresses such as salinity tolerance, plant stature, and other factors affecting productivity; quality factors such as higher oil or protein content; as well as culinary and other factors of cultural importance. These traits are both important to farmers and of major global significance as they are introduced into many modern varieties.

For example, wild relatives together with weedy species which have evolved over a long period of time and have coevolved with pests and diseases contributed greatly to plant improvement (Harlan 1981). Plant breeders commonly use wild species as gene donors to improve pest and disease resistance among cultivated species.

2.4 Rapid Decline of Plant Genetic Resource Diversity

The loss of genetic diversity (also called “genetic erosion”) includes the loss of individual genes and the loss of particular combinations of genes. This causes reduced biological fitness and increased chances of extinction.

The 2008 International Union for Conservation of Nature (IUCN) Red List states that of 12,055 species of plants assessed, 8,457 (or 70%) are currently threatened with extinction (IUCN 2009).

Since the 1960s, a significant decline of varieties and plant species cultivated in agriculture has led to the rapid loss of PGR that hold lesser economic interest or solely local interest. The ongoing erosion of PGR has decreased the intra-specific genetic diversity of many crops. According to recent Food and Agriculture Organization (FAO) (1997) estimates, 8.75% of the genetic diversity of crop plants was lost in the last century. A survey by the ETC group (Erosion Technology and Conservation group) found that approximately 97% of PGR have been lost in the last 80 years.

2.5 Causes of Plant Genetic Resource Decline

According to the FAO, the causes of genetic erosion in crops are tabulated by country.
Table 1 [ PDF 10.5KB | 1 page ]

Concerning food crops, genetic vulnerability and genetic erosion are mainly caused by: (i) excessive genetic uniformity of a few high yielding modern varieties, (ii) collateral damages caused by conventional agriculture, (iii) contamination by genetically engineered (GE) crops, and (iv) global climate change.

(i) Genetic erosion resulting from excessive genetic uniformity in crops

Perhaps the most important factor affecting PGR decline is the displacement of local cultivars by improved varieties, and the displacement of local crops altogether by crops that do better on the market. Other factors include habitat destruction affecting the wild gene pool, changing cropping patterns, and the effects of long periods of droughts. As old varieties in farmers' fields are replaced by newer ones, genetic erosion frequently occurs because the genes and particular combinations of genes (e.g., of gene complexes) found in the diverse farmers' varieties are not contained in the modern high-yielding varieties.

It is known that many of today's widely planted modern varieties of food crops are impressively uniform genetically and are therefore vulnerable. The extent of uniformity is not always apparent because pedigrees are not always available, even for the most popular cultivars. In addition, data on areas sown with different cultivars of the same crop are not usually available. Uniformity per se is not dangerous, for some crop cultivars are remarkably stable.³ However, the dangers of planting large areas with a genetically uniform crop variety must be recognized, as these varieties could suddenly become uniformly susceptible to new pathogen races and be wiped out. The most famous example of this is the potato famine of 1845–1848, when a pandemic of late blight (Phytophthera infestans) wiped out the potato crop in Europe and North America.

(ii) Collateral damages caused by conventional agriculture

The absence of genetic variation in hybrid varieties of modern agriculture has led to the spread at an alarming rate of plant pests and diseases. This has caused the gradual and widespread extinction of traditional varieties and landraces grown nearby and those not receiving pesticides, like hybrids.

The excitement surrounding high-yielding hybrid varieties so captivated scientists and farmers that few foresaw the resulting displacement of indigenous genetic resources or their eventual extinction. The role of farmer as protector of crucial gene species such as sorghum, millet, buckwheat and beans was forgotten. Every effort was made to replace local varieties with high yielding ones, viewing the former as primitive.

(iii) Genetic vulnerability caused by the cross-contamination by GE crops

A new phenomenon may threaten the genetic diversity of the seed supply: the contamination of landraces and traditional seeds by DNA sequences derived from GE crop varieties.

In the US and other Western countries, there are a handful of examples of genes from genetically modified (GM) varieties found at low levels in non-GM varieties of some major crops grown nearby, raising the possibility of widespread contamination of food crops. Among the potential contaminants are genes from crops engineered to produce drugs, plastics, and vaccines.

In fact, contamination events are inevitable. Gene flow is a regular and natural occurrence among plants in any ecosystem; if a gene is released, it will escape to other varieties of the same crop or to its wild relatives. It is clear that zero contamination is impossible at present and that there is no way to ensure that food crops are not contaminated, for example by errant pollen that possibly contains new drug genes or herbicide-resistant genes. According to the degree of gene flow, the serious possibility of healthy gene pool erosion exists if genes from pharmaceutical and industrial crops contaminate the seeds of food crops at a significant level.

There are broad implications to the recognition that plant genetic diversity is shrinking rapidly and that the seed supply is open to contamination by low levels of a wide variety of GE sequences.

First, seeds reproduce and carry genes into future generations. Every season of seed production offers new opportunities for the crossing and exchange of genes or the introduction of new genes. In the case of GE, transgenic sequences that enter the seed supply of traditional crop varieties will be perpetuated and will accumulate over time in plants where they are not expected and could be difficult to control.

Second, seeds are the wellspring of our food system, the base upon which we improve crops and the source to which we return when crops fail. Non-contaminated seeds will be our only recourse if prevailing beliefs about the safety of GE seeds proves wrong.

Unless some part of our seed supply is preserved with a broad genetic base and free of GE sequences, our ability to change course if GE goes awry will be severely hampered. Prompt action is needed to protect traditional and landraces seed production from such sources of contamination.

(iv) The threat of global climate change

Climate change is already forcing plant species to adapt either by shifting habitats, changing life cycles or developing new physical traits. The species that are unable to adapt are facing extinction. Climate change threatens food crops as well as the few remaining landraces and wild relatives of key crops, a valuable source of genetic diversity. As a result, human dependence on wild relatives will intensify as the climate becomes harsher.

Farmers—especially smallholder farmers—are among the first to suffer from climate change. Changing weather patterns increase the frequency of droughts, floods and storms, which destroys farmlands, stock and rural dwellings. Plant species are disappearing at an unprecedented pace already. Farmers have to adjust to these changes by adapting their seeds and usual production systems to an unpredictable situation. Moreover, droughts and floods are leading to harvest failures, increasing the number of people that go hungry in developing countries.

According to the FAO, global warming is likely to lead to a serious decline in agriculture production in tropical areas (up to 30% to 50% in Senegal and in India) and to the acceleration of farmland desertification. On the other hand, huge areas in Russia and Canada will turn into arable land for the first time in human history, yet it is still unknown how these regions will be able to grow crops (FAO 1997).

Given the importance of the climate-biodiversity link, conservation through sustainable use of the traditional and landraces varieties that are especially resilient to climate change can strengthen and improve the ability of ecosystems to deal with increasing climatic pressures. At the same time, the increased flood and drought under climate change is contributing to higher level of species loss and therefore conservation efforts are ever more important.

2.6 Consequences of Gene Pool Erosion

The erosion of PGR diversity poses a severe threat to the world's food security in the long term as the loss of landraces and traditional varieties will affect negatively the ability of agriculture to adjust itself to climate change and its effects.

The extinction of plants in a species could potentially mean an undiscovered cure for cancer, an overlooked new antibiotic drug (like the antibiotic discovered in the soils of the threatened New Jersey Pine Barrens Natural Area) or a forgotten disease-resistant plant species (like the perennial disease-resistant corn found in Mexico) and therefore is a serious problem.

If lost, the particular combination of genes in a well-adapted landrace may be difficult or impossible to rebuild.

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