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Mechanisms of resistance to Phytophthora cinnamomi in clonal, micropropagated Eucalyptus marginata (1993)

CAHILL, D. M. ; BENNETT, I. J. ; McCOMB, J. A.

Oxford, UK : Blackwell Publishing Ltd

Plant pathology 42 (1993), S. 0

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ISSN: 1365-3059

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Plants of the eucalypt. Eucalyptus marginata. selected through a glasshouse screening procedure for resistance or susceptibility to Phytophthora cinnamomi, were established in tissue culture and micropropagated. After inoculation with P. cinnamomi, root lesions in clonal lines selected as resistant (RR) to P. cinnamomi were restricted and became contained within four days after inoculation while lesions in roots of those lines susceptible (SS) to P. cinnamomi continued to extend rapidly. Activity of phenylalanine ammonialyase (PAL) was increased above controls in root segments of the RR lines 48 h after inoculation with P. cinnamomi while activity in unselected seedlings and the SS lines was reduced or unchanged. After inoculation, lignin concentration was increased and reached high levels compared with uninoculated control levels in roots of the two RR lines tested. Constitutive levels of phenolics in roots of the RR lines were up to 94% higher than in seedling roots and levels were further increased after inoculation. Levels of phenolics in the other lines and seedlings were unaltered by inoculation. A line derived from resistant seedlings from a susceptible family (RS) had the highest constitutive levels of lignin, which were further increased after inoculation. Resistance to P. cinnamomi in clonally propagated E. marginata seedlings is based on similar mechanisms to those of field resistant species.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-3059.1993.tb02672.x

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Cell surface antigens ofPhytophthora spores: biological and taxonomic characterization (1994)

Hardham, A. R. ; Cahill, D. M. ; Cope, M. ; [et al.]

Springer

Protoplasma 181 (1994), S. 213-232

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ISSN: 1615-6102

Keywords: Oomycetes ; Pythium ; Phytophthora ; Monoclonal antibodies ; Surface antigens ; Immunocytochemistry

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary The oomycetes are a class of protists that produce biflagellate asexual zoospores. Members of the oomycetes have close phylogenetic affinities with the chromophyte algae and are widely divergent from the higher fungi. This review focuses on two genera,Phytophthora andPythium, which belong to the family Pythiaceae, and the order Peronosporales. These two genera contain many species that cause serious diseases in plants. Molecules on the surface of zoospores and cysts of these organisms are likely to play crucial roles in the infection of host plants. Knowledge of the properties of the surface of these cells should thus help increase our understanding of the infection process. Recent studies ofPhytophthora cinnamomi andPythium aphanidermatum have used lectins to analyse surface carbohydrates and have generated monoclonal antibodies (MAbs) directed towards a variety of zoospore and cysts surface components. Labelling studies with these probes have detected molecular differences between the surface of the cell body and of the flagella of the zoospores. They have been used to follow changes in surface components during encystment, including the secretion of an adhesive that bonds the spores to the host surface. Binding of lectin and antibody probes to the surface of living zoospores can induce encystment, giving evidence of cell receptors involved in this process. Freeze-substitution and immunolabelling studies have greatly augmented our understanding of the synthesis and assembly of the zoospore surface during zoosporogenesis. Synthesis of a variety of zoospore components begins when sporulation is induced. Cleavage of the multinucleate sporangium is achieved through the progressive extension of partitioning membranes, and a number of surface antigens are assembled onto the zoospore surface during cleavage. Comparisons of antibody binding to many isolates and species ofPhytophthora andPythium have revealed that surface components on zoospores and cysts exhibit a range of taxonomic specificities. Surface antigens or epitopes may occur on only a few isolates of a species; they may be species-specific, genus-specific or occur on the spores of both genera. Spore surface antigens thus promise to be of significant value for studies of the taxonomy and phylogeny of these protists, as well as for disease diagnosis.