Scientists report ‘huge’ loss of diversity


Scientists have been warning about declining crop diversity for over 100 years. A recent WWF report found that 75% of the food humans consume comes from just 12 plant sources and five animal sources, with three crops accounting for 60% of the plant-based calories in the total human diet.

Since 1900, FAO figures indicate that 75% of the genetic diversity of plants in agriculture has been lost. In Thailand, for example, the 16,000 varieties of rice formerly cultivated have fallen to only 37.

Crop diversity is a resource of critical importance for agriculture and human nutrition. This diversity keeps crops productive in the face of pests and disease, provides resilience during extreme weather and other shocks, and offers the potential to adapt to climate change and respond to new market demands.

Repeated harvesting of the same crop on the same land depletes nutrients in the soil, which usually requires more use of fertilizers and pesticides, which damage the environment.

But questions remain about the extent, causes and significance of this genetic loss.

A team of 15 scientists from various international research centers and universities set out 18 months ago to find answers to some of these lingering questions. Together, they carried out the “biggest ever review” of the evidence for changes in the diversity of cultures over time around the world.

The team examined hundreds of primary documentary sources published over the past 80 years to assess the loss of crop diversity, or “genetic erosion.” The global collaboration found that 95% of all studies reported a change in diversity, with almost 80% bearing evidence of loss of diversity.

Why are we witnessing genetic erosion in agriculture?

The review, published in the journal New phytologist, Economic, technological, climatic and political changes over the past 100 years have combined to lead to the loss of genetic diversity that researchers say is important to agriculture. This decline can be observed both in cultivated fields and in wild habitats, he noted.

Significantly, the research pointed out, the global diversity of the remaining crops continues to be threatened with erosion or extinction, with the genetic diversity of crops becoming “more homogeneous” in local landscapes internationally.

“The overall picture that emerges from our review is that of a huge loss over a relatively short period of time of traditional agricultural diversity, which has been nurtured by many crops across the world over the past 10,000 years. . “said lead author Colin Khoury, senior director for science and conservation at the San Diego Botanical Garden and a researcher at the Alliance of Bioversity International and the International Center for Tropical Agriculture (CIAT). “However, the image is also hopeful, because a considerable diversity of cultures persists and because it shows that agriculture can be re-diversified.”

The opportunity to “re-diversify”

Khoury has collaborated with scientists from international and national agricultural research centers in the United States, Colombia, Germany, Italy, Mexico and Peru, as well as with universities such as El Colegio de la Frontera Sur (Chiapas , Mexico), Ohio State University, Saint Louis University, University of Arizona, University of California Davis, University of Cambridge and University of Illinois to complete the study, ‘Genetic erosion of crops: understanding and responding to the loss of crop diversity‘.

“The extent of the loss of cultural diversity that we have observed in certain regions of the world underlines the importance of conserving this diversity outside these ecosystems as well as within them”said Luigi Guarino, scientific director of the Crop Trust and one of the study’s authors.

“Crop diversity collections such as those in agricultural genebanks and botanical gardens can mitigate local and regional losses, enable future restoration of diversity on farms, and preserve the availability of crops for future use by all. We need to strengthen these repositories and duplicate unique collections in other locations to insure against the risk of loss ”,he said.

There are approximately 1,750 genebanks worldwide, now over 7 million samples of plant diversity, with botanic gardens, universities, nonprofits, community seed banks and local conservation networks. contributing more to ex situconservation.

However, according to the researchers, more work is needed to conserve all of the diversity at risk of disappearing from farmers’ fields and, in the case of wild relatives of crops, the progenitors and wild cousins ​​of crops. grasslands, forests and other natural habitats.

Diversity remains high where varieties are valued

The study analyzed the evolution of the diversity of traditional plant varieties grown on farms, modern plant varieties in agriculture, wild relatives of plants grown in their natural habitats and plant genetic resources held in ex situconservation deposits. The magnitude of change over time in these environments, while considerable, varied by culture, location, and analytical approach. And the researchers noted that some contexts were more favorable to genetic variety.

“The good news is that while we have found evidence of a huge loss of diversity over the past decades in each of the environments we have studied, we have also seen significant maintenance of this diversity in some contexts, and even marked increases in specific cases’said Stephen Brush, second author of the study and professor emeritus of human ecology and former senior adviser for international agricultural development at UC Davis.

The diversity of traditional crops remains high on farms and in gardens where they are valued for their “unique agricultural and societal uses”. One-third of 139 studies of changes in traditional crop varieties reported maintenance of diversity over time, and almost a quarter found evidence of new diversity emerging.

In addition, crop breeders have made “significant strides” towards cultivar diversification of modern crops in recent decades, the review noted.

“For crop diversity to continue to evolve alongside pests and diseases, in response to climate change, and to meet the demands for improved crops that provide both economic products and ecological services, we need to step up support for conservation efforts in situ, or on the ground, as well as ex situ ”,Co-author suggested Allison Miller, Fellow and Principal Investigator at the Danforth Plant Science Center and Professor of Biology at the University of Saint Louis.

“Looking at the global evolution of crop diversity that underpins people’s food security and nutrition, it is evident that there has been a significant loss, but also that the tools, methods and knowledge exist. to stop its new erosion ”,concludes Khoury. “It’s a question of priorities and resources. Going further and starting to reverse the trend towards diversity, however, is a much bigger task. It requires nothing less than reframe our food systems, and even the societies they nurture, as processes that support diversity. “


Genetic erosion of crops: understanding and responding to the loss of crop diversity

New plant scientist

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