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Rhamphicarpa fistulosa (Hochst.) Benth. is a parasitic member of the Scrophulariaceae occurring sporadically on rice and other cereal crops in tropical Africa. Relatively little is known about this parasite, and some aspects concerning its life cycle and its impact on crops are reported in the present paper. The size, the shape and the seedcoat ornamentation of R. fistulosa are described and compared with those of Striga spp. The seeds do not require a host root exudate to stimulate germination but do require light. As in the case of Striga spp., they show a period of dormancy of at least 6 months. When the parasite roots come into close contact with a host root, they swell and develop haustoria, which form a direct xylem connection between host and parasite. In vitro and pot culture experiments establish that R. fistulosa is a facultative parasite, as it is able to complete its life cycle without a host plant. However, plants growing under these conditions are much smaller and produce only a few seeds. Field observations indicate that in some places, R. fistulosa can destroy cereals. The agronomic hazard represented by this member of the Scrophulariaceae is discussed.

Summary.The haustorial structure of three African parasitic members of the family Scrophulariaceae (Buchnera hispida, Rhamphicarpa fistulosa, and Striga hermonthica) has been studied with regard to the interface between haustoria and the invaded host roots. Immunocytochemical observations at the light and electron microscopical level were carried out with monoclonal antibodies against pectin, JIM5, JIM7, and hydroxyproline-rich glycoprotein (HRGP), LM1. Lignins have been visualized by phloroglucinolhydrochloric acid staining. At the margin of the lateral interface (contact area of host root cortex and parasite cells), JIM5-and JIM7-1abelled substances accumulate between parasite papillae and the host root surface indicating that pectins are implicated in sealing the parasite to the attacked host organ. The lateral interface is characterized by the presence of compressed, necrotic host cells, whereas the central interface (contact area between host stele and parasite ceils) is generally devoid of host cell remnants. Phenolic substances and/or lignins can be found at the site of penetration of the haustorium into the host root. These observations and the fact that HRGPs accumulate at the host side of the interface support the view of, at least, a partial defense reaction in the invaded host root tissues. Within haustoria, HRGPs were restricted to differentiating xylem elements, implying a spatio-temporal regulation of HRGPs in developmental processes.