Answer: oidium

AnswerCrossword Clue
oidiumone of the conidia that are borne in chains by certain fungi
oidium(in certain fungi) a thin-walled spore derived from the fragmentation of a hypha into its component cells
oidiumpowdery mildew especially of grapes caused by an oidium
oidiuma type of fungus (any of the major group of lower plants)