Damping-off
Damping-off, a disease of seeds, seedlings, and cuttings that can occur when the soil is overwatered or when the seeds are planted too close together. In pre-emergence damping-off, the germinating seed rots before sprouting through the soil. In postemergence damping-off, the seedlings or cuttings topple over and die because of rot, which appears as a dark area at the base of the stems.
Some kinds of damping-off are caused by fungi, such as those of the genera Fusarium and Rhizoctonia, of the phylum Deuteromycota; other kinds are caused by protists, such as those of the genera Phytophthera and Pythium, of the phylum Oomycota.