Which one of the following is monoecious?

Select the correct combination of the statements (i-iv) regarding the characteristics of certain organisms.
(i)  Methanogens are archaebacteria which produce methane in marshy areas.
(ii)  Nostoc is a filamentous blue-green alga which fixes atmospheric nitrogen.
(iii)  Chemosynthetic autotrophic bacteria synthesize cellulose from glucose.
(iv)  Mycoplasma lack a cell wall and can survive without oxygen.
The correct statements are

Black (stem) rust of wheat is caused by

Which one of the following is most appropriately defined ?