Haustorial ultrastructure and morphology of Melampsorella and Thekopsora areolata

The morphology and ultrastructure of dikaryotic haustoria (D-haustoria) of Melampsorella caryophyllacearum and Melampsorella symphyti (Uredinales, Pucciniastraceae) were found to be different. The haustorium of M. caryophyllacearum was branched apically and the haustorial neck was sheathed by a fold of the extrahaustorial membrane. A system of filamentous structures was present in the matrix fold around the neck. In M. symphyti, no such matrix fold was present and the haustorial body was unbranched. D-haustoria of Thekopsora areolata were bulbous and unbranched. They differed from D-haustoria of other Thekopsora species by the presence of a matrix fold at the haustorial neck. Melampsorella, Thekopsora and Pucciniastrum are the only pucciniastraceous genera, so far that revealed different haustorial types. The systematic implications are discussed.