Structure of the Host-Parasite Interface of Boschniakia Hookeri Walpers (Orobanchaceae)

Abstract

The host-parasite interface of Boschniakia hookeriWalpers (Orobanchaceae) parasitic on Gaultheria shallon Pursh is radially grooved, and shows several significant contrasts to that known for Orobanche. Unlike the latter, Boschniakia has a large, perennial interface, and the host surface is made up almost entirely of differentiated xylem. The xylem-xylem contact involves both fiber-tracheids and vessel elements on the host side, and vessel elements on that of the parasite; open xylem connections across the interface are relatively common. The phloic continuity and transfer-like cells known from Orobanche have no counterpart in Boschniakia. No meristematic zone is present along the interface, the initiation of the latter being brought about by an early inversion of the host cambium. The term "tuber", even though not completely appropriate, is used for the swollen Boschniakia organ directly above the interface, and the term "soma" rejected.

Roots in Corynaea (Balanophoraceae)

“…It is illuminating to refer to the epicortical roots which develop in many species of another group of parasites, i.e., certain mistletoes in the tropics and subtropics (Kuijt 1969(Kuijt , 1982. While these organs continue to be somewhat controversial, they are endogenous in origin and their apices are covered by a thin but distinctive root cap (Heil 1926;unpubl.…”

“…inf.). They are not articulate, and lateral roots are produced endogenously (Kuijt 1965). A11 evidence thus points to a root-like nature.…”

“…We would also draw attention to a striking parallel in another group of holoparasites, Orobanchaceae. In Epijugus Nutall (Cooke & Schively 1904) and in some species of Orobunche L. (Kuijt 1969), the haustorial tuber produces large numbers of short, exogenous, ageotropic root-like organs which lack root hairs and which, in contrast to other Orobanche species, d o not produce haustorial contacts. Their function remains unknown but, since they represent a transitional situation in a morphological series that finds its extreme expression in the totally rootless tuber of Boschniukiu C .…”

“…The family of holoparasites, Balanophoraceae, consists of about twenty genera, most of which are very small or even monotypic. All are terrestrial root parasites of extremely reduced morphology (Kuijt 1969), both in flowers and, except for haustorial attachments, in vegetative structures. Leaves are reduced to fleshy scales or, in a few genera, are quite absent.…”

Gross xylem structure of the interface of Psittacanthus ramiflorus (Loranthaceae) with its hosts and with a hyperparasite

“…The major interfacial contact in the haustoria of parasitic angiosperms always seems to be parenchymatous in nature, even though xylem–xylem continuity has also been documented in numerous cases (Calvin, 1967; Kuijt & Toth, 1976; Pate, Kuo & Davidson, 1990). However, it is conceivable that the cambial zones of the two partners show a degree of continuity, as is the case in Boschniakia (Orobanchaceae), where a similar but much smaller woodrose is produced on the host (Kuijt & Toth, 1985). Clearly, our observations need to be followed up with more detailed observations if a full understanding of the interface of Psittacanthus is to be gained.…”