Nitrogen relations of the sorghum‐Striga hermonthica host‐parasite association: germination, attachment and early growth

Abstract

SUMMARYThe probability of the parasitic angiosperm Striga hermonthica achieving a successful union with its sorghum host is in part dependent on the concentration of ammonium nitrate in the growth medium. Germination rates were higher with 1 mM than with 3 mM ammonium nitrate. Ammonium nitrate did not influence either the stability of active components of host root exudate, or their perception by the parasite's seed. High concentrations of ammonium nitrate did not significantly reduce the leakage of potassium ions from sorghum roots (although patterns of exudation may differ between groups of compounds). Thus, it appears that ammonium nitrate reduced either the production of stimulatory compounds, or their specific leakage from host roots. Subsequent attachment of the parasite radicle and early growth of the plant were also lower at higher concentration of ammonium nitrate, and possible reasons for these observations are discussed.

Influence of the host on three sub‐Arctic annual facultative root hemiparasites

“…Stimulation of parasite photosynthesis following attachment seems to be a consequence of a greater availability of reduced nitrogen; those R. minor plants which grow on nitrogen rich hosts (nitrogen fixers) have greater concentrations of leaf nitrogen and chlorophyll, and have greater lightsaturated rates of photosynthesis than those which grow on non-fixing hosts (Seel et al, 1993a). Parasites associated with nitrogen-rich hosts may thus be more autotrophic for carbon than those oti nitrogen-poor hosts (Cechin & Press, 1993), but they are presumahly still largely dependent on the host for mineral solutes.…”

Interactions between the parasitic angiosperm Orobanche aegyptiaca and its tomato host: growth and biomass allocation

“…These studies have shown that Striga can radically reduce host growth, and alter biomass allocation. Grain yield and stem biomass are the most severely reduced, whilst leaf and root biomass are less affected (Graves, Press & Stewart, 1989;Cechin & Press, 1993. In addition, lower rates of photosynthesis have been observed in infected cereals than in uninfected plants, under both laboratory and field conditions (Press, Tuohy & Stewart, 1987 ;Cechin & Press, 1994;Gurney, Press & Ransom, 1995).…”

Do inorganic solutes limit growth of the facultative hemiparasite Rhinanthus minor L in the absence of a host?

“…O/«xMy//a«f/?0, parasites may also be governed by the supply ot prior to the development of functional haustoria solutes. Positive linear correlations between nitrogen (Pate Kuo & Davidson, 1990;Smith, Dudley & supply from the host and light saturated rates of Lynn 1990) Some hemiparasitic genera are truly photosynthesis of root hemiparasites have been facult'ative and can complete tbeir life-cycle in the reported (Cechin & Press, 1993;Press et al, 1993), absence of a bost. Such occurrences are compara-and in the mistletoes there are data to suggest that tively rare in nature, but do exist, as seen in a study water use efficiency (WUE) may be controlled by of the Mediterranean hemiparasitic annual Bartsia host nitrogen supply (Schulze & Ehlennger, 1984)t rixago .…”