ANY delay in harvesting wheat is always frustrating for growers, but prolonged periods of wetness can cause pre-harvest sprouting within the grain head, thus lowering the quality, yield and test weight of the wheat and triggering substantial economic loss.
When the wheat seed prematurely germinates in the field, the starch and protein are degraded, making the damaged seed unacceptable for human food products. Furthermore, pre-harvest sprout damage can also continue during shipping and storing. Harvested wheat containing 4% or more damaged kernels is ineligible for food quality designation, which reduces the grower's selling price by 20-50%.
Bikram Gill, Kansas State University (KSU) professor of plant pathology and director of the Wheat Genetics Resource Center, said white wheat production suffers a direct loss of $1 billion annually due to pre-harvest sprouting.
Gill said consumers prefer white wheat over the predominant red wheat because white wheat lacks the more bitter flavor associated with red wheat. Millers also prefer white wheat to red because it produces more flour when ground. The problem is that white wheat is very susceptible to pre-harvest sprouting.
According to the U.S. Department of Agriculture, approximately 82% of the world's wheat is used for food or seed, while the remaining 18% is used for animal feed or residual use. Historically, in major wheat-producing regions, pre-harvest sprouting occurs in three to four years out of 10.
Since ill-timed rain is impossible for growers to control, the occurrence and severity of pre-harvest sprouting remains unpredictable. For example, this year's winter wheat is being reported in good condition for parts of North Dakota and Montana, while samples from Michigan have indicated poor quality due to pre-harvest sprout damage.
Varieties of wheat naturally do contain some degree of pre-harvest sprout tolerance, but not at equal levels. This is why a new study conducted by scientists at KSU and USDA's Agricultural Research Service (ARS) is focused on the common problem of pre-harvest sprouting in wheat.
The research team, led by Gill, found and cloned a gene in wheat named "PHS" that prevents the plant from sprouting pre-harvest.
"This is great news because pre-harvest sprouting is a very difficult trait for wheat breeders to handle through breeding alone," Gill said. "With this study, they will have a gene marker to expedite the breeding of wheat that will not have this problem."
Gill conducted the study with Guihau Bai, a researcher with the ARS Hard Winter Wheat Genetics Research Unit, adjunct professor of agronomy at KSU and the study's lead author. Also involved were plant pathology professor Harold Trick, agronomy research associate Shubing Liu, senior plant pathology scientist Sunish Sehgal, research assistant professor Jiarui Li and doctoral agronomy student Meng Lin — all from KSU — plus Jianming Yu at Iowa State University.
"There has been demand for white wheat in Kansas for more than 30 years," Gill said. "The very first year white wheat was grown in the state, though, there was rain in June, and then there was pre-harvest sprouting and a significant loss. The white wheat industry has not recovered since and has been hesitant to try again. I think that this gene is a big step toward establishing a white wheat industry in Kansas."
Gill said identifying the PHS gene creates greater assurance before planting a crop that it will be resistant to pre-harvest sprouting once it grows a year later. Wheat breeders can now bring a small tissue sample of a wheat plant into a lab and test whether it has the pre-harvest sprouting resistance gene rather than finding out after the crop grows.
Much of the work to isolate the PHS gene came from Gill and his colleagues' efforts to fully sequence the genome of common wheat. Wheat is the only major food plant whose genome has not been sequenced.
Researchers were able to study sequenced segments of the common wheat genome and look for a naturally occurring resistance gene. Gill said without the sequenced segments, finding the PHS gene would have been impossible
Their study, "Cloning & Characterization of a Critical Regulator for Pre-Harvest Sprouting in Wheat," appeared in a recent issue of the scientific journal Genetics. n