A simple method to differentiate Diplodia macrospora from D. maydis in corn seeds is described in this paper. The white rots these fungi cause on corn (Zea mays) ear and grains have identical symptoms. However, D. macrospora and D. maydis give rise to colonies of different colours when infected seeds are incubated on filter paper. Corn seeds are disinfested with sodium hypochloride, placed in gerboxes containing two layers of wet filter paper, and then incubated at 25 ± 2 ºC. After 15 days, colonies of D. macrospora remain white to beige while those of D. maydis, originally white, turn dark and form picnidia. Because current seeds pathology tests do not differentiate these fungus species, we believe that D. macrospora may have been mistakenly diagnosed as D. maydis.
