New insights concerning the ecology and the biology of Rhamphicarpa fistulosa (Scrophulariaceae)

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.