Reevaluation of grading standards and discounts for fungus‐damaged soybean seeds

Abstract

AbstractThe proportion of off‐colored seed is a primary quality‐rating factor that influences the market grade of soybean,Glycine max L. Merrill. Off‐colors, attributed to biological agents such as fungi and viruses, are visual characteristics that arbitrarily result in lower grade ratings when soybeans show more than ten percent discoloration. These damaged seeds may be further classified under current United States Department of Agriculture, Federal Grain Inspection Service standards as: moldy, weathered, bicolored, mottled, or other colors. Presently, all types of fungal damage and virus symptoms are evaluated equally in the application of discount schedules at grain‐elevators. However, recent information shows that superficial discoloration caused by some biological agents does not lower grain quality. Indeed, methods are available to distinguish those symptoms that actually reduce seed quality from those that are more cosmetic in nature. This communication provides guidance on fungi that are involved most often in seed damage or discoloration. The following organisms are listed in descending order of importance:Phomopsis longicolla, Alternaria, Nematospora coryli, Fusarium graminearum, Colletotrichum, andCercospora kikuchii. Discoloration caused byPeronospora manchurica (downy mildew) and the soybean mosaic virus have limited effect on seed quality. Discoloration caused by each of these agents may be identified by recognizable characteristics. Therefore, knowledge of the relative impact of these organisms on seed quality should be practiced in the application of soybean grading standards and discount schedules.