Waxy Spring Wheats Developed

Germplasm can be used to develop commercially-adapted varieties for specialized and improved uses

Nineteen germplasm lines of waxy spring wheat jointly developed by USDA Agricultural Research Service and university scientists are now available for breeding commercial cultivars with traits for high-amylopectin (HA) starch.

Starch rich in this glucose polymer has excellent water retention, digestibility, gelatinization and stickiness, features that make it useful as a sauce thickener, emulsifier and shelf-life extender.

Most HA starch now comes from waxy corn and rice varieties. But waxy wheat starch also shows promise, especially as a flour blending ingredient. Ongoing research suggests it helps bread stay fresh, and imparts desirable softness to certain Asian wet noodles, like Udon noodles. It may also produce better flour tortillas and other grain-based foods.

The problem is that there are no existing commercial waxy spring wheats, only experimental ones, and these are poorly adapted to U.S. growing regions, according to plant geneticist Robert Graybosch, with ARS’ Wheat, Sorghum and Forage Research Unit in Lincoln, Neb.

Graybosch worked with ARS and state agricultural experiment station collaborators in Nebraska, Idaho, and North Dakota (including Bill Berzonsky, hard white spring and specialty wheat breeder at North Dakota State University) to overcome the problem by crossbreeding Asian waxy wheat mutants with American spring wheats.

Wheat starch is normally 75% amylopectin and 25% amylose, which are types of glucose polymer. The 19 resulting waxy lines inhibit an enzyme that produces amylose. Thus, the starch is virtually 100% amylopectin.

Sixteen of the new lines are classified as hard wheats and three as soft, based on kernel evaluation scores. Fifteen have red-colored grains, while the remaining four have either red or white grains.

In field tests, including plot trials near Fargo, the wheat lines’ average grain yields ranged from a high of about 54 bushels per acre to a low of 39 bu/ac. “These materials are developed for wheat breeders to take to the next level; it’s germplasm for breeders to use as parents to make crosses and breed cultivars adapted to different growing regions,” says Graybosch. The regionally-adapted commercial varieties could then be grown, possibly as “identity-preserved,” for specialized applications.

There is no “wax” in the waxy wheats; waxy just refers to the missing gene responsible for amylose starch.  The waxy term is actually a carryover term from similar work in corn, when kernels without the amylose gene in the starch had a “waxy” appearance.

Berzonsky has one waxy line under development that includes the white wheat Argent in its background.  There are also some existing varieties that have partial waxy properties.  A partial waxy wheat may have more end-use functionality than a complete waxy variety; further research will help sort that out. Still, it is possible that this research will in time result in starch performance become another basis for wheat variety analysis and comparison, just like protein is now. 

USDA-ARS and NDSU crop scientists have also been involved in developing waxy durum, which holds promise as a replacement to vegetable shortening in making bread, without losing the desired properties the shortening confers to bread. Read more details on waxy durum online at www.smallgrains.org .  Click on the “Prairie Grains” link, then “2002” under the archives, then “April, 2002” for the article “USDA-ARS, NDSU Researchers Develop New Waxy Durum.”

This image shows the difference between waxy and normal wheats.  Kernels are sliced open to expose the starchy endosperm, which is the part that will become flour after milling. A drop of iodine solution is applied to each kernel. In the normal wheat, the starch is composed of two types of glucose polymers, amylose and amylopectin. The amylose will trap the iodine and turn a dark blue/black color, as evident by the kernels in the bottom of the photo. In the waxy kernels on top, there is no amylose. The starch is composed only of amylopectin, and it will trap far less iodine, turning a reddish-brown color instead. “These staining differences are quite distinct and are used in our breeding program to isolate waxy lines,” says USDA-ARS plant geneticist Robert Graybosch, Lincoln, Neb. These differences in starch properties in turn convey differences in cooking properties of the starch.