Number Crunching Through Maize


Number Crunching Through Maize

Geneticist uses statistics to breed more nutritious strains of corn

Jing Jin

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As an undergraduate student at the University of Virginia, Prof. Edward Buckler, plant breeding and genetics, studied archaeology and biology. Later as a graduate student at the University of Missouri-Columbia, he was especially compelled by the genetic variation of the natural world.

“Most life forms don’t vary in concrete ways. It isn’t like there’s one tall form of a tree and one short form. There’s gradations everywhere in between […] There is no single gene that’s going to determine everything, and that is where statistics comes in,” Buckler said.

At age eight, Buckler was already programming and using computers to analyze data, but it wasn’t until his archaeology training that he was struck by the usefulness of statistics for summarizing the distribution of archaeological sites.

For simplicity’s sake, geneticists of the 20th century focused on traits that were controlled by one or two genes, such as human eye color or maize — more commonly known as corn — kernel color. Most traits, however, are polygenic and controlled by more than one gene.

Buckler now focuses on corn genetics. Corn has 30,000 genes and tremendous diversity as a species.

“Any two corn plants are more divergent than you and I are from chimpanzees,” Buckler said.

The diversity of plant species comes from the sheer population numbers that have evolved over millions of years, during which they have built up genetic variation while adapting to more environments. Humans, on the other hand, only date back to 200,000 years.

Buckler has helped to develop an association mapping technique to identify the genetic origins of complex traits, providing insight into how organisms control their natural variation.

“We find useful genetic variation; [in one or two years] we can create markers or models to select for that genetic variation and start to put it into breeding programs,” Buckler said.

Buckler is currently collaborating with the breeders Kevin Pixley of the International Maize and Wheat Improvement Center and Tobert Rocheford of Purdue University to fortify corn varieties with higher levels of provitamin A.

Corn contains carotenoids, including beta-carotene, which can be converted to vitamin A. The varying level of carotenoids is reflected in the kernel color; white kernels have almost no carotenoids, while orange kernels have almost as much carotenoids as carrots.

Corn is the dominant subsistence crop in Sub-Saharan Africa, and variants deficient in vitamin A can lead to health disorders for millions of children. Some varieties have as little as 0.1 micrograms of beta-carotene per gram of corn, while the target is 15 micrograms.

Using association mapping to screen corn for levels of beta-carotene, Buckler discovered two different genes and two variants of those genes that can increase provitamin A 16-fold.

HarvestPlus, which partners with Buckler’s group, is conducting trials in Zambia in anticipation of a 2014 deployment of a corn variety that “pretty much looks like a carrot [and] that probably will make a very important nutritional contribution,” Buckler said.

Since the method requires no genetic engineering and simply makes use of natural variation, “the route to acceptance is much quicker,” Buckler said. Cultural obstacles do, however, exist.

“HarvestPlus has done a lot of research using market surveys. A lot of it is just education. They’re finding out that people like white or they like orange. They don’t like pale yellow,” Buckler said.

Buckler’s most recent work is on corn’s flowering time, which affects the plant’s adaptation to different environments across the globe, and leaf angle, which affects the plant’s sunlight capture and growth.

Buckler’s overarching goals are to “understand how you go from 2.3 billion letters to a trait,” to continue making agriculture more sustainable, and to create “something really novel.” Perennial maize, for example, uses less nitrogen and is more drought-tolerant. 

“We’re all essentially trying to make food in a more efficient, more sustainable way. If we can solve the problem with genetics that can be replicated around the world, that’s a lot better solution,” Buckler said.