This poor 'Ice Punch' poinsettia cutting had several pathogens isolated including Phytophthora sp., Pythium sp., and Thielaviopsis.
OSU Plant Clinic image, 2013.
See:
Rhododendron - Cutting Rots
Poinsettia (Euphorbia pulcherrima) - Bacterial Stem Rot
Poinsettia (Euphorbia pulcherrima) - Pythium Root Rot
Poinsettia (Euphorbia pulcherrima) - Root and Stem Rot