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Root Parasite (root + parasite)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Host,parasite relations of an angiospermous root parasite (Thonningia sanguinea Vahl) in logged and unlogged sites of Budongo forest reserve, western Uganda

AFRICAN JOURNAL OF ECOLOGY, Issue 3 2009
Concy Acen Olanya
Abstract Host,parasite relationships of an angiospermous root parasite (Thonningia sanguinea) were investigated in logged and unlogged sites of Budongo Forest Reserve. Host trees were identified and their diameters measured in 20 × 20 m plots established randomly in sites where the parasites were presumed to occur. The distance of the point of attachment of the parasite from the base of the host stem was determined and overstorey density measured at the centre of each plot. There were more parasites in the logged than in the unlogged sites (878 and 425 individual parasites ha,1 respectively). The parasite was not host specific but Alchornea laxiflora (Benth) Pax and K.Hoffm, Celtis mildbraedii Engl and Lasiodiscus mildbraedii Engl had relatively more parasites than other species. The parasite could be found within a radius of 2 m from the base of the host stem. The diameter of hosts ranged from 1 to 95 cm. There was a positive correlation between overstorey density and occurrence of T. sanguinea. Conservation of T. sanguinea, therefore, requires maintenance of intact forests with closed canopies rather than logged sites with many gaps and hence low overstorey density. Résumé On a étudié les relations hôte-parasite d'un angiosperme parasite des racines (Thonningia sanguinea) sur des sites exploités ou non de la Réserve forestière de Budongo. On a identifié les arbres hôtes et on a mesuré leur diamètre dans des parcelles de 20 × 20 m établies au hasard dans des sites où le parasite était supposé se trouver. La distance entre le point d'ancrage du parasite et la base du tronc de l'hôte fut déterminée, et la densité de la végétation aérienne fut mesurée au centre de chaque parcelle. Il y avait plus de parasites dans les parcelles exploitées que dans les parcelles nonexploitées (878 et 425 parasites par ha, respectivement). Le parasite n'était pas spécifique de l'hôte, mais Alchornea laxiflora (Benth) Pax et K.Hoffm, Celtis mildbraedii Engl et Lasiodiscus mildbraedii Engl avaient relativement plus de parasites que d'autres espèces. Le parasite peut se trouver dans un rayon de deux mètres de la base du tronc de l'hôte. Le diamètre du tronc de l'hôte variait de 1 à 95 cm. Il y avait une corrélation positive entre la densité de la végétation aérienne et l'occurrence de T. sanguinea. Donc, la conservation de T. sanguinea requiert la préservation de forêts intactes avec des canopées fermées plutôt que des sites exploités avec des nombreuses clairières et donc, une faible densité de couverture végétale. [source]

Host-driven divergence in the parasitic plant Orobanche minor Sm. (Orobanchaceae)

MOLECULAR ECOLOGY, Issue 19 2008
C. J. THOROGOOD
Abstract Many parasitic angiosperms have a broad host range and are therefore considered to be host generalists. Orobanche minor is a nonphotosynthetic root parasite that attacks a range of hosts from taxonomically disparate families. In the present study, we show that O. minor sensu lato may comprise distinct, genetically divergent races isolated by the different ecologies of their hosts. Using a three-pronged approach, we tested the hypothesis that intraspecific taxa O. minor var. minor and O. minor ssp. maritima parasitizing either clover (Trifolium pratense) or sea carrot (Daucus carota ssp. gummifer), respectively, are in allopatric isolation. Morphometric analysis revealed evidence of divergence but this was insufficient to define discrete, host-specific taxa. Intersimple sequence repeat (ISSR) marker-based data provided stronger evidence of divergence, suggesting that populations were isolated from gene flow. Phylogenetic analysis, using sequence-characterized amplified region (SCAR) markers derived from ISSR loci, provided strong evidence for divergence by clearly differentiating sea carrot-specific clades and mixed-host clades. Low levels of intrapopulation SCAR marker sequence variation and floral morphology suggest that populations on different hosts are probably selfing and inbreeding. Morphologically cryptic Orobanche taxa may therefore be isolated from gene flow by host ecology. Together, these data suggest that host specificity may be an important driver of allopatric speciation in parasitic plants. [source]

Conditioning period, CO2 and GR24 influence ethylene biosynthesis and germination of Striga hermonthica

PHYSIOLOGIA PLANTARUM, Issue 1 2000
Abdel Gabbar T. Babiker
Germination of witchweed (Striga hermonthica [Del.] Benth), an important root parasite on poaceous crops, requires pretreatment ,conditioning' in a warm moist environment and a subsequent exposure to a stimulant. The roles of conditioning period, CO2 and a strigol analogue (GR24) in ethylene biosynthesis and germination of the parasite were investigated. Conditioning increased the seeds' capacity to oxidize exogenous 1-aminocyclopropane-1-carboxylic acid (ACC). Exogenous CO2 increased the seeds capacity to oxidize ACC by 3- to 9-fold. A combination of GR24 and ACC increased ethylene production by more than 3-fold in comparison with the rates obtained using these compounds separately. Aminoethoxyvinylglycine (AVG) completely inhibited ethylene induction by GR24, but not by ACC. A GR24 treatment, made subsequent to conditioning in GR24, did not induce ethylene. However, seeds conditioned in GR24 and then given 1 mM ACC produced 293 nl l,1 ethylene. ACC oxidase (ACCO) activity in crude extracts was increased by conditioning and CO2. The enzyme displayed an absolute requirement for ascorbate. Absence of exogenous Fe2+ reduced enzyme activity only by 14%. GR24 applied during conditioning reduced germination in response to a subsequent GR24 treatment. ACC was, invariably, less effective in inducing S. hermonthica germination than GR24 even at concentrations which induce more ethylene than concurrent GR24 treatments. The results are consistent with a model in which conditioning removes a restriction on the ethylene biosynthetic pathway in S. hermonthica seeds. GR24 modulates the key enzymes in ethylene biosynthesis. The stimulant suppresses ethylene biosynthesis in unconditioned seeds and promotes it in conditioned ones. Germination of S. hermonthica results from the joint action of GR24 and the ethylene it induces. [source]