Sorghum height research offers insight for wider crop improvement

A team of researchers from several US institutions explored the genetic interaction behind sorghum height to answer questions about both how heterosis works and to ultimately improve the process of plant breeding, said lead researcher Jianming Yu, associate professor of agronomy and Pioneer Distinguished Chair in Maize Breeding at Iowa State University.

“Heterosis, the better performance of a hybrid than either of its parents, can be traced back to Charles Darwin, and has been of great interest to biologists,” ​said researchers. “Hybrids derived from diverse inbred lines generally show higher growth rate and yield and better resistance to biotic and abiotic stresses.”​

Ultimately, the research may be able to provide new tools to plant breeders, they said.

“Besides identifying a specific genetic example of heterosis, our research indicated that integrated molecular dissection of complex traits in different population types can enable plant breeders to fine tune the breeding process for crop production,”​ they said.  

Understanding heterosis can be compared with driving a car, Yu told us. You don’t have to understand how the car engine works to drive a car – or cross breed plants – but if you want to design a better, more efficient car – or plant – it is essential to know how the engine works.

“Heterosis has been used for different plants, but we don’t understand fully what is going on,” ​said Yu. “We need to dig into the mechanism and that will benefit future research.”​

Height and heterosis link​

The work started with an earlier experience with sorghum, said Yu. That project raised questions about the height differences found in hybrid offspring sorghum plants. Although the parent plants were close in height, the resulting offspring could be several feet taller or shorter than the original plants.

“Sorghum is also showing heterosis,” ​he said. “Plant height is the number one trait, and it is a trait that has a lot of importance.” ​

It also can be simpler to track the genetics involved in height differences than those for grain yield, he said.

In the study, researchers said they examined repulsion linkage of height traits in hybrid sorghum plants.

Repulsion linkage is sometimes called ‘linkage drag,’ and relates to the crossing of two parent plants that have both dominant and recessive alleles in similar areas of their genetic structure, said Yu.

In the parent or non-hybrid plants, the two traits would have canceled each other and each parent plant, in this case, would have moderate height, he said.

But, in cross breeding the parent plants, depending on the location of the dominant and recessive traits, the resulting hybrid offspring may benefit and only display the taller or dominate genes, he said. The taller offspring plant would be an example of heterosis.

In its work, the group identified the genetic location of one height gene and then tracked its interaction with computer modeling and a specific breeding program where offspring plant traits were monitored, said researchers. They used that data to demonstrate why heterosis was taking place.

One of the crossed hybrid plants was 44cm taller than the taller parent plant and offered a “35% high-parent heterosis,”​ they said. In a second cross, the resulting hybrid was 30cm taller or having a “19% high-parent heterosis.”​

Additionally, understanding the linkage puts an emphasis on what is happening with the plant’s genetics, said Yu. “It’s better to quantify the genetic material of individuals, and not be confused by the appearance of the trait,”​ he added.

Wider applications​

An additional goal of the research was to encourage other scientists to track and document instances of heterosis, said Yu. “There’s still limited examples of heterosis,”​ he added.

Tracking other traits that show it can be used to better build and design breeding programs for feed crop development, he said.

His ongoing work seeks to apply some of the lessons learned about heterosis in sorghum to corn with the eventual goal of improving grain yield, he said.

“We’re continuing to study grain yield in maize and to see if you can find more on repulsion linkage and heterosis – we want to see how prevalent it is,”​ he said. “We sought out genetic mechanisms, but not the biological mechanism. We know we have genes, the next steps will be the genes and the biological pathway, and how those two are impacting, and looking to figure out heterosis in corn.” ​

Source: Proceedings of the National Academy of Sciences​

Title: Dissecting repulsion linkage in the dwarfing gene Dw3 region for sorghum plant height provides insights into heterosis​

DOI: doi/10.1073/pnas.1509229112​

Authors: Xin Li, Xianran Li, Eyal Fridman, Tesfaye T. Tesso, and Jianming Yu,