Genetic mapping, new variety, food-related research brighten crop's outlook
Genetic linkage map of proso millet with 18 genes of eight desirable traits (such as lodging, grain shattering, seed size) using 93 progeny lines derived from a hybrid between Huntsman, a popular Nebraska proso millet variety, and Minsum, an old proso millet variety from Minnesota. The names of DNA markers and genes are on right hand side and genetic distances (measured in centi Morgan or cM) between the markers are on left hand side of each chromosome. Locations of the genes between a pair of markers are indicated by arrows.
By David Ostdiek, Communications Associate
Panhandle Research and Extension Center
The nation’s only proso millet breeding program, based at the University of Nebraska Panhandle Research and Extension Center, is making progress toward modern breeding of this low-water-use alternative crop for dryland farmers.
Several recent milestones in research might allow for faster development of new proso millet varieties, while improving prospects for finding new markets in food processing industries, according to Dr. Dipak Santra, alternative crops breeding specialist at the Panhandle Center.
Dipak Santra, alternative crops breeding specialist at the Panhandle Center, makes a hybrid in the greenhouse between a tall variety of proso millet and a short variety to identify genes for plant height.
Proso millet is the most important and common alternative crop where irrigation water use is limited. It uses the least amount of water to produce a bushel of grains among all cereals. It fits into the wheat-based dryland crop rotation of western Nebraska because it is highly adapted to growing conditions here: it has a short growing season, requires less water and can help improve yields in other crops in the rotation, such as wheat, corn and sunflower.
But planted acreage is limited by demand for bird seed (primarily domestic), resulting extreme price volatility.
Nebraska, Colorado, and South Dakota are the major U.S. producers of proso millet. Nebraska typically has one-third to one-fourth of the nation’s acreage, according to the National Agricultural Statistics Service (NASS). The state’s growers usually harvest 100,000 to 150,000 acres annually, producing 1.2 million to almost 4.5 million bushels.
Proso millet contributes about $12 million annually to the Panhandle economy. With acreage and price swings, Nebraska’s production value can range from $4 million to $21 million, according to NASS.
In addition to domestic bird seed companies, a significant amount of the U.S. crop is sold for export to European and southeast Asian countries. The United States exports about $16 million worth of proso millet per year.
Though not widely used in the United States, proso millet is a desirable food ingredient because it is gluten-free, a benefit to people with celiac disease, according to Santra. For diabetics, it has a low glycemic index (it is slower to increase blood glucose levels). He said there are also reports of anti-cholesterol properties due to presence of some specific proteins.
Proso millet also is healthy for the environment too, Santra said. Producing a crop requires lower inputs than other cereals such as corn or wheat. Therefore, it is environmentally sustainable, which is critical considering potential climate change, he said.
A major milestone toward future genetic improvements in proso millet production is completion of the first genetic map for the crop (see photo). Santra and several UNL colleagues worked on the project for several years, identifying DNA markers that signal the locations of genes that control desirable agronomic traits, such as high yield, larger seed size, quicker maturation, and tolerance to lodging, seed shattering and drought.
The results of the genetic mapping project are published in an article in March issue of Molecular Breeding.
Santosh Rajput, who worked in Scottsbluff for several years as a graduate student under Santra’s supervision, worked on the project, spending countless hours in Santra’s laboratory and research plots with numerous varieties of proso millet. He received his doctorate in 2015 and now works as plant breeder for Dryland Genetics, LLC in Ames, Iowa. The third author is James Schnable of the Beadle Center on the UNL campus.
With genetic mapping of proso map completed, Santra said, it will be more efficient to breed new millet varieties with traits desired by producers. These traits are controlled by genes. The quickest way to locate desirable genes on a strand of DNA is to find the (easier to identify) markers that signal the (difficult to identify) genes’ locations.
The genetic map makes it possible to identify and locate genes that control a desirable trait. Santra provided an example: to find a line of proso millet that is less likely to lodge (lay down in the field), a plant breeder might need to screen 10,000 millet lines. Each line would need to be grown in the field and selected by visual inspection – which plants in which plots displayed the desired trait?
But if a plant breeder can locate markers associated with genes that control the trait, the thousands of millet lines can be screened in a greenhouse, and their genetic material screened in the laboratory. In one month, the plant breeder could narrow the choices of breeding lines to, say, 100, compared to four months in the field using traditional methods.
“And you have a 95 percent probability that those plants will have the desired trait, based on marker location,” Santra said. Then the 100 lines that have the desired trait can be tested in the field, under replicated conditions.
In the real world, plant breeders are often selecting for multiple traits. The just-published paper identified which DNA markers are associated with a number of commercially desirable traits.
For example, in selection for three traits – shattering tolerance, high yield, and drought tolerance – using DNA markers that have been identified and mapped might allow a plant breeder to narrow 48 potential lines to only two lines that contain all three markers, before testing in the field, rather than “shooting in the dark” and planting trial plots with all 48 lines.
Genetic mapping has been completed in other animals and plants, including humans and other agricultural crops, as long as 25 years ago. But it had not been accomplished for proso millet until now.
Proso has 18 chromosomes, compared to 10 in corn, 12 in rice, 21 in wheat, 11 in dry beans, and seven in field pea.
Two dryland fields in Cheyenne County during the drought of 2012 illustrate the low water requirement of proso millet (top) compared to corn (bottom), which is high water use and could not survive.
The genetic mapping project comes on the heels of several other research projects that signal progress in improving proso millet and establishing it as a food crop for human consumption.
A new variety of waxy proso millet (amylose-free starch) was registered in late 2014. Plateau is a cross between Huntsman, a popular, high-yielding variety, and a Chinese line that is high in waxy starches but not well adapted to growing conditions in the High Plains.
Waxy millet is desirable in some Asian markets for use in food, such as sponge bread, that has sticky qualities, Santra said.
Plateau was described in an article in the Journal of Plant Registrations. It was developed by Santra and colleagues from the Nebraska Agricultural Experiment Station. Faculty and staff from University of Wyoming, Colorado State University, and USDA-ARS of Lincoln and Akron, Colo., assisted in trials and laboratory evaluations.
“Introduction of a proso millet variety with novel end-use characteristics such as waxy starch will open new opportunities for using proso millet in the food-and-beverage industry,” Santra said. “Plateau displayed grain yields competitive with those of currently grown proso varieties in the region.”
If Plateau and other millet varieties are to gain wider use in the food and beverage industry, food manufacturers will need to know how they react to processing. That is the goal of another research project, which measured how millet reacted to extrusion.
According to Santra, extrusion is necessary in order to make instant breakfast cereals. So, the idea was to find out whether proso millet can be used for instant breakfast cereals, similar to oat, barley and other grains.
Research conducted by the UNL Food Processing Center and Food Science and Technology Department was described in a 2015 article in the International Journal of Food Science and Technology.
The research measured effects of feed moisture and extruder screw speed and temperature on physical characteristics and antioxidant activity of extruded proso millet flour.
Santra collaborated in the project conducted by Devin Rose (lead scientist), Associate Professor in the UNL Food Science and Technology, Paridhi Gulati, the graduate student of Rose and Steven A. Weier of the Food Processing Center, as well as several others.
Various types of millets are consumed as porridges, soups, flat breads and in Asian and African countries. Potential food uses in the United States include weaning mixes, pasta, and breads and cookies in combination with wheat flower.
Extrusion is a versatile, cost-effective process that can be used to create cereals and snacks from grains. The only current reported work on proso millet extrusion is to evaluate the effect of extrusion on proso lipids.
“Due to a similar proximate composition with other commonly extruded grains (rice, corn, wheat), extrusion of proso millet may be a viable way of increasing proso millet utilization in human foods.”