Rust and Smut are caused by:

Rust and smut are caused by Puccinia and Ustilago respectively. Puccinia is an obligate parasite which causes rust diseases in many cereals, millets. Ustilago causes smut disease by the formation of black coloured spores called smut spores. The black coloured spores are exposed as soon as they are formed in loose smut but in covered smut the smut spores are not immediately exposed.