- Connections among gene and physical differences established.
- Role of growing environment considered.
- Further step will use genomic selection.
A NEW study of sorghum, led by Stephen Kresovich and Geoff Morris of the University of South Carolina, aspires to make this crop an invaluable asset in the climate change challenge.
Just published in the Proceedings of the National Academy of Sciences (PNAS), the paper puts genetic tools into the hands of scientists and plant breeders to help accelerate their ability to adapt sorghum to new conditions.
A hardy cereal crop that was first domesticated in the Horn of Africa some 10,000 years ago, sorghum is now cultivated worldwide. Sorghum is a particularly drought-tolerant grain and an essential part of the diet for 500 million people, chiefly in sub-Saharan Africa and India. In the U.S., where it is primarily grown for livestock feed, sorghum's climate resilience was highlighted during the 2012 summer drought, the announcement said.
A large international effort to decode the genome of the species cultivated for food, Sorghum bicolor, was published in the journal Nature in 2009. That genome represents the genetic accounting of a single individual of sorghum.
However, the focus of the current effort was to establish the connections among gene differences and physical differences; a detailed understanding of those connections will constitute a tremendous tool for plant breeders, the announcement said.
The team behind the paper published in PNAS -- which also included researchers at Cornell University, the International Crops Research Institute for the Semi-Arid Tropics in India and Niger, the University of Illinois and the U.S. Department of Agriculture -- used genotyping-by-sequencing to determine the individual genetic makeup of 971 sorghum varieties taken from worldwide seed collections.
The researchers identified more than a quarter-million single-nucleotide polymorphisms where individual variants of sorghum can differ, according to the University of South Carolina.
The results were possible thanks to a tremendous genetic resource that was built over many years. For almost a century, sorghum seeds from a variety of international locations have been stored in seed banks, with dates and geographic origins often noted with each sample.
"We're taking advantage of the incredible diversity found in the gene bank," said Morris, a research assistant professor at the University of South Carolina and lead author on the paper.
One subject of particular scrutiny in the paper was the genetic control of the panicle, the structure on the top of the plant that holds the grains, the announcement said. This structure is important for successful breeding, particularly when climate is a consideration.
Closely packed grains, for example, are preferred for maximum crop yield in dry areas, but in places with abundant rainfall, more spacing is desirable to allow grains to dry out more readily and to reduce crop losses from moisture-caused disease.
The researchers identified genes that likely contribute to this physical feature, and they also mapped them geographically according to the source of the original seed. The result was insight into how different variants of the genes spread according to regional climates, which varied widely in the study from the edge of the Sahara Desert to the rainy highlands of east Africa.
The results will "provide resources for everyone around the world who breeds sorghum," Morris said. "The goal is to do it faster than the way it's been done traditionally, which takes years of growing and crossing and testing."
A further step will involve genomic selection, another collaborative effort planned for the coming year that will again involve Kresovich, who is the SmartState endowed chair of genomics at the University of South Carolina and senior author on the PNAS paper.
Using genomic selection, in which computers are used to select the most promising candidates to test in the field, "you might be able to take years off the breeding cycle," Morris said. "Instead of having to grow thousands of varieties, you test thousands of varieties 'in silico' and pick a few hundred of the best for growing the next generation."