Abstract
Forms of resistance and pathogenic specialization in interactions between wheat and its stem and leaf rust Fungi have been selected for analysis with two hypotheses in mind. One is that phytoalexin formation is a universal defence mechanism in plants; the other is that resistance is elicited specifically by products of avirulent strains of pathogens. A search for phytoalexins in wheat, using a range of extraction and separation procedures and a number of forms of expression of resistance, has indicated the presence of several inhibitors of fungal development but has yielded very little evidence for post-infectional increases in the amounts of these inhibitors. No evidence for the formation of phytoalexins in wheat has been obtained. Hypersensitivity has been confirmed as being closely associated with the expression of most forms of resistance studied. Recent work with some very rapidly expressed forms of resistance to rust fungi has implicated lignification as a component of active defence in wheat, a finding in agreement with those of other workers. The expression of resistance conferred by the Lr20 gene towards avirulent strains of the leaf rust fungus was the principal subject of explorations for elicitors. Histological observations of the sequence of events in fungal and wheat cells suggested the action of rust strain and Lr20-specific elicitors in bringing about hypersensitivity. Experimental manipulations involving heat treatments or use of epidermis-free segments of leaves incubated on infected mesophylls gave results consistent with this interpretation. Attempts to extract specific elicitors from infected leaves failed but yielded non-specific elicitors. Non-specific elicitors have been obtained in intercellular washing fluids of leaves infected with strains of both the leaf and stem rust fungi. They have also been obtained from extracts of germ tubes of both species of fungus. Although not specific for any known resistance gene, the elicitors are selective for a character determined by a factor on chromosome 5 A in some wheat cultivars. A role for the non-specific elicitors as incompatibility factors between rust fungi and wheat is suggested. A revised hypothesis is presented in order to explain the evolution of pathogenesis in rust fungi towards wheat and it is discussed in relation to concepts of basic compatibility between pathogens and their hosts, as proposed also by others. CONTENTS Summary 233 I. Introduction 234 II. Working Ideas and Hypotheses 234 III. The Search for Phytoalexins 235 IV. Elicitation of Resistance 237 V. Revised Hypothesis 240 Acknowledgements 242 References 242.
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Claims 13
Claim · model-written summary
Searches found several inhibitors of fungal development in wheat.
- Taxon
- wheat
Triticum aestivume1 - Interactor
- fungale0pathogen
- Outcome
- presence of several inhibitors of fungal developmente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“has indicated the presence of several inhibitors of fungal development”
e1“A search for phytoalexins in wheat”
Claim · model-written summary
Searches found little evidence of postinfection increases in these inhibitors.
- Taxon
- wheatTriticum aestivume1
- Outcome
- post-infectional increases in the amounts of these inhibitorse0
- Qualifier
- very little evidencee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“has yielded very little evidence for post-infectional increases in the amounts of these inhibitors”
e1“A search for phytoalexins in wheat”
Claim · model-written summary
No evidence was obtained for phytoalexin formation in wheat.
- Taxon
- wheatTriticum aestivume0
- Outcome
- formation of phytoalexinse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“No evidence for the formation of phytoalexins in wheat has been obtained.”
Claim · model-written summary
Hypersensitivity was closely associated with most studied forms of wheat resistance.
- Taxon
- wheatTriticum aestivume1
- Interactor
- stem and leaf rust Fungie1pathogen
- Outcome
- expression of most forms of resistance studiede0
- Qualifier
- Hypersensitivitye0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Hypersensitivity has been confirmed as being closely associated with the expression of most forms of resistance studied.”
e1“interactions between wheat and its stem and leaf rust Fungi”
Claim · model-written summary
Lignification was implicated as part of active wheat defence against rust fungi.
- Taxon
- wheatTriticum aestivume0
- Interactor
- rust fungie1pathogen
- Outcome
- active defencee0
- Qualifier
- lignificatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“has implicated lignification as a component of active defence in wheat”
e1“forms of resistance to rust fungi”
Claim · model-written summary
Histology suggested rust-strain and Lr20-specific elicitors cause hypersensitivity.
- Taxon
- wheatTriticum aestivume0
- Interactor
- rust straine0pathogen
- Gene
- Lr20e0
- Outcome
- hypersensitivitye0
- Qualifier
- rust strain and Lr20-specific elicitorse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Histological observations of the sequence of events in fungal and wheat cells suggested the action of rust strain and Lr20-specific elicitors in bringing about hypersensitivity.”
Claim · model-written summary
Heat and epidermis-free leaf experiments were consistent with the specific-elicitor interpretation.
- Taxon
- wheatTriticum aestivume1
- Treatment
- heat treatments or use of epidermis-free segments of leaves incubated on infected mesophyllse0
- Outcome
- results consistent with this interpretatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Experimental manipulations involving heat treatments or use of epidermis-free segments of leaves incubated on infected mesophylls gave results consistent with this interpretation.”
e1“fungal and wheat cells suggested the action of rust strain and Lr20-specific elicitors”
Claim · model-written summary
Attempts to extract specific elicitors from infected wheat leaves failed.
- Taxon
- wheatTriticum aestivume1
- Outcome
- extract specific elicitors from infected leaves failede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Attempts to extract specific elicitors from infected leaves failed”
e1“fungal and wheat cells”
Claim · model-written summary
Extracts of infected leaves yielded nonspecific elicitors.
- Taxon
- wheatTriticum aestivume1
- Outcome
- yielded non-specific elicitorse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Attempts to extract specific elicitors from infected leaves failed but yielded non-specific elicitors.”
e1“fungal and wheat cells”
Claim · model-written summary
Nonspecific elicitors were obtained from washing fluids of leaves infected by leaf and stem rust.
- Taxon
- wheatTriticum aestivume1
- Organ / stage
- leavese0
- Interactor
- leaf and stem rust fungie0pathogen
- Outcome
- Non-specific elicitorse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Non-specific elicitors have been obtained in intercellular washing fluids of leaves infected with strains of both the leaf and stem rust fungi.”
e1“interactions between wheat and its stem and leaf rust Fungi”
Claim · model-written summary
Nonspecific elicitors were also obtained from germ tubes of both rust species.
- Taxon
- wheatTriticum aestivume2
- Interactor
- leaf and stem rust fungie1pathogen
- Outcome
- obtained from extracts of germ tubes of both species of funguse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“They have also been obtained from extracts of germ tubes of both species of fungus.”
e1“Non-specific elicitors have been obtained in intercellular washing fluids of leaves infected with strains of both the leaf and stem rust fungi.”
e2“interactions between wheat and its stem and leaf rust Fungi”
Claim · model-written summary
Nonspecific elicitors selected for a chromosome 5 A determined character in some wheat cultivars.
- Taxon
- wheatTriticum aestivume0
- Gene
- factor on chromosome 5 Ae0
- Outcome
- selective for a charactere0
- Qualifier
- some wheat cultivarse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the elicitors are selective for a character determined by a factor on chromosome 5 A in some wheat cultivars.”
Claim · model-written summary
The authors suggest nonspecific elicitors act as incompatibility factors between rust fungi and wheat.
- Taxon
- wheatTriticum aestivume0
- Interactor
- rust fungie0pathogen
- Outcome
- incompatibility factorse0
- Qualifier
- non-specific elicitorse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“A role for the non-specific elicitors as incompatibility factors between rust fungi and wheat is suggested.”