Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2003
Publication Date: 11/1/2003
Citation: Morris, C.F., Massa, A. 2003. Puroindoline genotype of the u.s. national institute of standards & technology reference material 8441, wheat hardness. Cereal Chemistry. 80:674-678.
Interpretive Summary: Wheat end-use quality is frequently a reflection of its intrinsic endosperm texture, or hardness. Hardness affects tempering and milling properties, and the uses to which flour can be put in bakeries. Hardness is a subjective measurement. Hence, samples of defined, well-known and agreed-upon hardness values are used to calibrate various instruments that measure hardness. These samples are available from the National Institute of Standards and Technology (SRM8441, "Wheat Hardness") and represent five hard wheats and five soft wheats. Since these samples became available, the underlaying molecular-genetic basis for hardness was discovered. This research defines the molecular genetic basis for variation in endosperm texture in this standard set of samples. Particle Size Index (PSI, Method 55-30) and Quadrumat flour milling, NIR, SKCS and Quadrumat break flour yield grouped the hard and soft varieties into discrete texture classes; PSI did not separate completely the two classes. The four methods for measuring hardness are highly intercorrelated, but each was variably influenced by minor, secondary factor(s). Two of the five hard wheats lack the protein "puroindoline a" and are harder than the hard winter varieties which have both "puroindoline a" and "puroindoline b", but with a mutation in the puroindoline b protein. Among soft wheats, all had normal compliments of puroindoline and b and variation in softness was due to other, undefined causes. Overall, eastern U.S. and Western U.S. cultivars were different.
Technical Abstract: Grain hardness (kernel texture) is of central importance in the quality and utilization of wheat (Triticum aestivum L.) grain. Two major classes, soft and hard, are delineated in commerce and in the Official U.S. Standards for Grain. However, measures of grain hardness are empirical and require reference materials for instrument standardization. For AACC approved methods employing near-infrared reflectance (NIR) and the Single Kernel Characterization System (39-70A and 55-31, respectively), such reference materials were prepared by the U.S. Dept. of Agriculture Federal Grain Inspection Service. The material was comprised of genetically-pure commercial grain lots of five soft and five hard wheat varieties, and was made available through the National Institute of Standards and Technology (SRM 8441, 'Wheat Hardness'). However, since their establishment, the molecular-genetic basis of wheat grain hardness has been shown to result from puroindoline a and b. Consequently, we sought to define the puroindoline genotype of these 10 wheat varieties, and more fully characterize their kernel texture via Particle Size Index (PSI, Method 55-30) and Quadrumat flour milling. NIR, SKCS and Quadrumat break flour yield grouped the hard and soft varieties into discrete texture classes; PSI did not separate completely the two classes. Although all four of these methods of texture measurement were highly inter-correlated, each was variably influenced by some minor, secondary factor(s). Among the hard wheats, the two hard red spring wheat varieties which possess the Pina-D1b ('a-null') hardness allele were harder than the hard red winter wheat varieties which possess the Pinb-D1b allele based on NIR, PSI and break flour yield. Among the soft wheat samples, SKCS grouped the eastern soft red winter varieties separate from the western soft white. A more complete understanding of texture-related properties of these and future wheat samples is vital to the use and calibration of kernel texture-measuring instruments.