Sources of Seed Coat Color Variants Found in Certified Wheat Seed.

Kernel color is a key factor in determining grade and class of wheat.  In Washington State, seed samples are inspected as part of the seed certification process, for presence and number of seeds exhibiting off-type coloring. Exceeding specified limits results in a loss of certification, possible reduction in market grade, and a corresponding loss of profit.  The occurrence of off-type seeds is therefore a cause of concern for all parties involved in seed production. Red seed coat color in wheat is controlled by dominant R loci, three homoeologous genes located on the long arms of chromosomes 3A (R-A1), 3B (R-B1) and 3D (R-D1). Color variation has been found to be dependent on the number of R1 homoeoalleles, and also on unknown environmental interactions. Normal and suspected off-type seeds from certified varieties were digitally photographed, grown, and genotyped at the R1 homoeoloci. Additional genetic marker analysis was completed to determine variety purity. Results indicated no discernible pattern of environmental interactions. Red seeds were found to contain red alleles; white seeds contained white alleles. The two groups also were easily separated by differing red, green and blue (rgb) values obtained from color images of each seed.  Results from additional genetic marker tests were variety specific and implied two primary sources, or reasons, for seeds of off-type color. The first source found was simple contamination from genetically different varieties. The second source was true-to-type varieties that are heterogeneous at one or more  R1 homoeolocus,  indicating  heterozygosity at R1 loci was not monitored in the breeding process. These findings highlight the precaution and care needed at every step of the breeding and seed production processes to limit contamination.