Genetic bridges to the future

As severe weather and evolving crop diseases threaten farmers’ livelihoods and global food security, scientists are using novel DNA tools and informatics to unearth high-value traits from vast maize and wheat seed collections, for use in breeding climate-resilient varieties to feed the future.

genetic diversity graphic

Thousands of years ago, the domestication of maize and wheat from wild grasses sustained the rise of great civilizations. Migration, trade and conquest eventually spread those grains to every corner of the world. Some varieties became tolerant to dry conditions, others to heat, frost, local diseases, and long or short growing seasons, over centuries of selection and breeding by farmers.

Realizing that modern varieties would supplant these locally-adapted “landraces,” breeders and other specialists began to gather and conserve them in organized, cataloged collections in refrigerated genebanks.

“The genetic variation stored in the CIMMYT genebank, comprising 150,000 wheat collections and 28,000 maize collections, is crucial to developing the stress resistant maize and wheat varieties of the future,” says Kevin Pixley, Director of CIMMYT’s Genetic Resources Program and the Seeds of Discovery (SeeD) initiative, “but plant breeders are often reluctant to use that diversity.”

The reason, explains Pixley, is that the unique and valuable traits from landraces come with many genes for less desirable, wild characteristics, which have to be removed through repeated crosses and selection. This multiplies the time and cost of creating elite varieties.

“It’s like extracting and purifying gold from deep mines, so engineers and artisans can craft it into specialized products for industrial or personal use,” Pixley explains, adding that DNA markers and other advanced technologies are now bringing the “gold” of seed collections within reach of crop breeders.

Maize collections held at the CIMMYT genebank in Mexico.

Maize collections held at the CIMMYT genebank in Mexico.

“To help breeders, CIMMYT is crossing landraces with elite varieties to develop ‘bridging germplasm’ halfway in performance between unimproved and elite lines, but with increased stress adaptation or quality traits from the landraces.”

More than 5,000 maize landraces from the genebank have been evaluated using DNA markers for one or more high-value breeding traits, and 350 of these are being used to develop bridging germplasm with enhanced drought tolerance, improved nutritional and end-use quality, and resistance to devastating diseases such as Maize Lethal Necrosis or the tar spot complex.

“The tar spot complex-resistant bridging germplasm will become available to breeders in 2017, and bridging germplasm for other traits will follow,” Pixley says.

In the case of wheat, CIMMYT and partners have screened over 100,000 genebank seed collections for samples that carry drought or heat tolerance and disease resistance. More than 1,000 are being used to develop bridging germplasm, according to Pixley: “Breeders in China, India, Iran, Kenya, Mexico, Pakistan, and the USA are already testing the selected collections and bridging germplasm for use in their programs.”

Examples of the wheat genetic diversity stored in the CIMMYT genebank.

Examples of the wheat genetic diversity
stored in the CIMMYT genebank.

This research is facilitated by the support of key donors such as: Mexico’s Secretaría de Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación (SAGARPA); the CGIAR Research Programs on Maize (MAIZE), Wheat (WHEAT) and Genebanks; the United Kingdom’s Biotechnology and Biological Sciences Research Council (BBSRC); the Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH and the Ministry of Foreign Affairs of Japan (MOFA).

This article originally appeared here in the CIMMYT 2015 Annual Report.

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