Initiation, Development and Structure of the Primary Haustorim in Striga gesnerioides (Scrophulariaceae)

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Abstract
A light-microscopic study is reported on the initiation, establishment and structure of the primary haustorium of Striga gesnerioides on the host, cowpea (Vigna unguiculata). The radicular apex of the germinated parasite seed dissolves its way through the host root cortex to the stele. Thus, it is converted into a primary haustorium. Some of the haustorial front-line cells in contact with the host endodermis penetrate into the stele and make contact with the xylem vessels. Differentiation of these haustorial cells into xylem vessels occurs and extends backwards through the median axial region of the haustorial tract in the host cortex to connect with the conductive xylem of the radicle outside the host root. Subsequently the parasite's plumule develops into a leafy shoot. On penetrating the stele of the host, the haustorium stimulates cell division in the host pericycle whose triggered proliferation together with expansion of the parasite haustorial tissues result in the formation of a large, tuberous primary haustorium. At various points of the host-parasite interface, differentiation of xylem elements occurs, presumably maximizing nutrient transfer from host to parasite. In spite of this, many proliferated host cells at the interface remain apparently meristematic showing densely-stained cytoplasm and prominent nuclei.

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