Seeds from plants infected by Anthracnose may or may not show discoloration. This summer, Anthracnose was more frequently observed in no-till fields compared with the past few years. Both pathogens also survive in crop residues and the use of tillage to bury the residues can reduce disease pressure. Purple seed stain is caused by Cercospora kikuchii . This fungus causes Cercospora leaf blight during a growing season.
Infected seeds have a pink to purple discoloration on their seed coats.
Seeds with 50 percent discoloration are considered to be poor quality. The pathogen also survives in crop residues. Finally, keep in mind that although the discoloration of seeds is used to identify possible diseases, it may not be reliable because other nonpathogenic factors also can cause discoloration. I have observed discolored seeds from pods having insect wounds. For a reliable identification, seed testing is needed.