Black piedra is caused by -

Ans. is 'a' i.e., Piedraia hortae o Piedra is an asymptomatic superficial fungal infection of the hair shaft also known as trichomycosis nodu- laris. Black piedra is caused by Piedraia hortae, whereas white piedra is caused by pathogenic species of the Trichosporon genus, namely Trichosporon asahii, Trichosporon ovoides, Trichosporon inkin, Trichosporon mucoides, Trichosporon asteroides, and Trichosporon cutaneum.