Cercospora leaf spot of soybean

Frogeye leaf spot, caused by Cercospora sojina, manifests on leaves as gray spots 3–6 mm in diameter with a dark border, on stems as sunken reddish-brown lesions, and on seeds as gray spots with a brown border. Purple seed stain, caused by the pathogen Cercospora kikuchii, is characterized by purple discoloration of the seed coat, seed cracking, as well as the appearance of purple spots on leaves and pods, and shriveling of the cotyledons.

Cercospora sojina is characterized by a system of differentiation into races and pathogenic groups (PG1–PG5), which determine the aggressiveness of isolates. In breeding for resistance, the Rcs3 gene plays a key role, providing effective protection against a wide range of pathogen races. Cultivar resistance is also controlled by loci linked to molecular SSR markers, such as Satt244 and Satt565.