Sources of Color Variation in Certification-Candidate Wheat Seed.

Kernel color is an important factor in determining grade and class of wheat (Triticum aestivum L.), and is dependent on the number of red R-1 homoeoalleles.  In certified seed programs, candidate seed samples are inspected during the certification process for presence and number of seeds exhibiting off-type coloring. Exceeding limits for color variation results in loss of certification. To determine if admixtures of genetically distinct varieties were the primary cause for color variation in the Washington certified seed program, normal and suspected off-type seeds were digitally photographed, grown, and genotyped at the R-1 homoeoloci. Additional genetic marker analysis was completed to determine variety purity.  Results were variety specific and implied three primary sources for seeds of off-type color. The first and major source found was admixtures of genetically different varieties. The second source was true-to-type varieties that were heterogeneous and heterozygous at one or more R-1 homoeolocus, indicating active color segregation. The last source of variation identified, was due to unknown environmental interactions in genetically pure samples. These findings highlight the precaution and care needed at every step of the breeding and seed production processes to limit contamination, and also suggest that current certification tests and procedures are not completely accurate in determining variety purity.