Mobilizing seed bank diversity for wheat improvement

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During centrifugation, the emulsion for DNA extraction separates into two distinct phases. Chloroform:octanol is more dense than water solutions, so it forms the lower (green) layer. It is also more chemically attractive to molecules such as proteins and polysaccharides. These are thus separated out from the DNA, which is contained in the upper aqueous phase. This clear solution is carefully transferred to fresh centrifuge tubes using a pipette. Photo credit: CIMMYT. See the "DNA extraction" set that this photo is part of for more information and images.A recent study by a global team of researchers from CIMMYT, ICARDA, and the Global Crop Diversity Trust has uncovered a treasure trove of wheat genetic diversity to address drought and rising temperatures—constraints that cut harvests for millions of farmers worldwide and which are growing more severe with each passing year.

The team studied the molecular diversity of 1,423 spring bread wheat accessions that represent major global production environments, using high quality genotyping-by-sequencing (GBS) loci and gene-based markers for various adaptive and quality traits.

They discovered thousands of new DNA marker variations in landraces known to be adapted to drought (1,273 novel GBS SNPs) and heat (4,473 novel GBS SNPs), opening the potential to enrich elite breeding lines with novel alleles for drought and heat tolerance. New allelic variation for vernalization and glutenin genes was also identified in 47 landraces from Afghanistan, India, Iran, Iraq, Pakistan, Turkmenistan, and Uzbekistan.

Mean diversity index (DI) estimates revealed that synthetic hexaploids—created by crossing wheat’s wild grass ancestor Aegilops tauschii with durum wheat—are genetically more diverse than elite lines (DI = 0.267) or landraces (DI = 0.245). Lines derived from such crosses are already playing an increasingly important role in global and national breeding programs.

Identifying and mobilizing useful genetic variation from germplasm banks to breeding programs is key to sustaining crop genetic improvement.  The results have already been used to select 200 diverse germplasm bank accessions for pre-breeding and allele mining of candidate genes associated with drought and heat stress tolerance, thus channeling novel variation into breeding pipelines.

Published in the paper Exploring and Mobilizing the Gene Bank Biodiversity for Wheat Improvement, the research is part of CIMMYT’s ongoing Seeds of Discovery project visioning towards the development of high yielding wheat varieties that address future challenges from climate change.

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