DEVELOPMENT AND STRUCTURE OF THE HAUSTORIUM OF THE PARASITE RHAMPHICARPA-FISTULOSA (SCROPHULARIACEAE)

Rhamphicarpa fistulosa (Hochst.) Benth. (Scrophulariaceae), a parasite of African cereals, develops secondary haustoria which penetrate the roots of the host plant. Light and electron microscopy have been used to study the structure and development of haustoria in this species, w hich, until now, have not been well characterized. Haustoria are initi ated in the hypodermis of the parasite roots. A meristematic strand is developed between the parasite root stele and the host-parasite inter face. From this strand, cells differentiate into xylem elements after penetration of the host root. Xylem differentiation follows an acropet al pattern. Mature haustoria are characterized by a continuous xylem b ridge between water conducting elements of parasite and host. A detail ed study of the host-parasite interface revealed the presence of colla psed and compressed host cells at the lateral interface (between paras ite cells and host cortex), whereas the central interface between para site cells and the host stele is almost devoid of host cell remnants. Implications of these observations for the penetration mechanisms are discussed.