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Evaluation of systemic plant protection mechanism induced by hypovirulent Rhizoctonia spp
Year:
2010
Source of publication :
Tel Aviv University
Authors :
Sharon, Michal
;
.
Volume :
Co-Authors:
Facilitators :
Freeman, Stanley
;
.
Katzir, Nurit
;
.
From page:
0
To page:
0
(
Total pages:
1
)
Abstract:

supervision by: prof. Sneh Baruch, Dr. Freeman Stanley, Dr.Katzir Nurit

It has been established thus far that protective Rhizoctonia isolates trigger defense-related responses in the plants they protect. To our knowledge, by now, no study has examined thoroughly which plant resistance pathways are induced in plants colonized by hypovirulent Rhizoctonia spp. isolates. The SAR (Systemic acquired resistance) pathway is effective mostly against biotrophic pathogens and involves PR (pathogenesis related) protein induction. It is usually induced in plants by biotrophic pathogens, SA (Salicylic acid – which is a key element in this pathway) and some chemical, such as BTH and Bion®. The ISR (Induced systemic resistance) is mostly effective against necrotrophic pathogens. It is usually induced in plants by rhizobacteria, necrotrophic pathogens, insects, and meJA (methyl jasmonate), – which is a key element of this pathway, along with ethylene. Phytoalexins production is sometimes associated with the ISR pathway, although phytoalexins can be induced in a separate pathway from ISR, and thus protect the plants in an independent way. The objective of the present work was to evaluate which of the induced systemic resistance pathways are involved in the protection of plants by hypovirulent Rhizoctonia spp. isolates against pathogenic Rhizoctonia. To establish this, it was first validated that the virulence levels of the isolates used in this study were very low on various plant species. Protection levels which the hypovirulent isolates induced on cucumber plants were evaluated when the pathogen was introduced at the same site as the hypovirulent isolate on the plant, or at a distance away, and it was revealed that although the protective hypovirulent isolates induced systemic resistance in the plants they colonize, it is most likely not the only method of protection involved. Local protections, which were not examined in this study, are probably an important part in the defense of plants by the hypovirulent Rhizoctonia spp. isolates. Extracts of radish plants colonized by one of the hypovirulent Rhizoctonia isolates inhibited growth of pathogenic Rhizoctonia and indicated the involvement of phytoalexins in the resistance induced by the hypovirulent isolates. Comparing changes in protection levels of Arabidopsis thaliana mutants defected in defense-related genes to the protection of wt plants by the same isolates revealed that A. thaliana mutants defected in prime genes involved in both SAR and ISR were protected to a lower extent than the wt plants. On the other hand, the protection rates of the wt plants were similar to the protection of a mutant whose SAR deficiency was compensated by ISR expression as a result of removing the inhibition on ISR (SALK-025198c mutant), and the protection of mutants constantly expressing SAR (snc1, CS6571) was decreased compared to wt. These results indicate that the systemic induced resistance is a substantial part of the protection mechanism of plants by colonization of hypovirulent isolates against pathogenic Rhizoctonia, and that the ISR pathway has a major role in this protection. Monitoring prime genes in the SAR, ISR, and phytoalexin production pathways, in plants inoculated with hypovirulent Rhizoctonia spp., showed elevated levels of Pr5 (SAR), Pdf1.2, Lox2, Lox1,Cori3 (ISR), and Pad3 (phytoalexin production) gene expression which indicated that all of those pathways are induced in hypovirulent-inoculated plants. When SAR or ISR were induced separately in plants through application of chemical inducers (Bion and meJA, respectively), only ISR protected the plants against pathogenic Rhizoctonia isolate, and this protection, though significant, was not high. Concluding this study: hypovirulent Rhizoctonia spp. Isolates induce SAR, ISR and phytoalexin production in plants they colonize. Even though the SAR pathway may protect plant against other pathogens, it is probably not a significant part in the defense of inoculated plants against pathogenic Rhizoctonia. Apart from inducing SAR, ISR and phytoalexin production it is likely that the protective hypovirulent isolates also defend the plants they colonize locally, and although local protection was not investigated in this work, it should be examined in future research. The high protection levels of plants by hypovirulent Rhizoctonia spp. isolates is probably due to the combination of various protection modes, local and systemic, physical and induced in the plant. Therefore, the comprehensive reaction of protection which is achieved by the hypovirulent isolates could not be reconstructed by application of chemical substances in conventional pest control.

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pathogenesis related protein, plant
Plant protections
Rhizoctonia spp.
Systemic acquired resistance
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Article number:
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Database:
Publication Type:
Dissertation
;
.
Language:
English
Editors' remarks:
ID:
43216
Last updated date:
02/03/2022 17:27
Creation date:
19/08/2019 11:37
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Scientific Publication
Evaluation of systemic plant protection mechanism induced by hypovirulent Rhizoctonia spp

supervision by: prof. Sneh Baruch, Dr. Freeman Stanley, Dr.Katzir Nurit

It has been established thus far that protective Rhizoctonia isolates trigger defense-related responses in the plants they protect. To our knowledge, by now, no study has examined thoroughly which plant resistance pathways are induced in plants colonized by hypovirulent Rhizoctonia spp. isolates. The SAR (Systemic acquired resistance) pathway is effective mostly against biotrophic pathogens and involves PR (pathogenesis related) protein induction. It is usually induced in plants by biotrophic pathogens, SA (Salicylic acid – which is a key element in this pathway) and some chemical, such as BTH and Bion®. The ISR (Induced systemic resistance) is mostly effective against necrotrophic pathogens. It is usually induced in plants by rhizobacteria, necrotrophic pathogens, insects, and meJA (methyl jasmonate), – which is a key element of this pathway, along with ethylene. Phytoalexins production is sometimes associated with the ISR pathway, although phytoalexins can be induced in a separate pathway from ISR, and thus protect the plants in an independent way. The objective of the present work was to evaluate which of the induced systemic resistance pathways are involved in the protection of plants by hypovirulent Rhizoctonia spp. isolates against pathogenic Rhizoctonia. To establish this, it was first validated that the virulence levels of the isolates used in this study were very low on various plant species. Protection levels which the hypovirulent isolates induced on cucumber plants were evaluated when the pathogen was introduced at the same site as the hypovirulent isolate on the plant, or at a distance away, and it was revealed that although the protective hypovirulent isolates induced systemic resistance in the plants they colonize, it is most likely not the only method of protection involved. Local protections, which were not examined in this study, are probably an important part in the defense of plants by the hypovirulent Rhizoctonia spp. isolates. Extracts of radish plants colonized by one of the hypovirulent Rhizoctonia isolates inhibited growth of pathogenic Rhizoctonia and indicated the involvement of phytoalexins in the resistance induced by the hypovirulent isolates. Comparing changes in protection levels of Arabidopsis thaliana mutants defected in defense-related genes to the protection of wt plants by the same isolates revealed that A. thaliana mutants defected in prime genes involved in both SAR and ISR were protected to a lower extent than the wt plants. On the other hand, the protection rates of the wt plants were similar to the protection of a mutant whose SAR deficiency was compensated by ISR expression as a result of removing the inhibition on ISR (SALK-025198c mutant), and the protection of mutants constantly expressing SAR (snc1, CS6571) was decreased compared to wt. These results indicate that the systemic induced resistance is a substantial part of the protection mechanism of plants by colonization of hypovirulent isolates against pathogenic Rhizoctonia, and that the ISR pathway has a major role in this protection. Monitoring prime genes in the SAR, ISR, and phytoalexin production pathways, in plants inoculated with hypovirulent Rhizoctonia spp., showed elevated levels of Pr5 (SAR), Pdf1.2, Lox2, Lox1,Cori3 (ISR), and Pad3 (phytoalexin production) gene expression which indicated that all of those pathways are induced in hypovirulent-inoculated plants. When SAR or ISR were induced separately in plants through application of chemical inducers (Bion and meJA, respectively), only ISR protected the plants against pathogenic Rhizoctonia isolate, and this protection, though significant, was not high. Concluding this study: hypovirulent Rhizoctonia spp. Isolates induce SAR, ISR and phytoalexin production in plants they colonize. Even though the SAR pathway may protect plant against other pathogens, it is probably not a significant part in the defense of inoculated plants against pathogenic Rhizoctonia. Apart from inducing SAR, ISR and phytoalexin production it is likely that the protective hypovirulent isolates also defend the plants they colonize locally, and although local protection was not investigated in this work, it should be examined in future research. The high protection levels of plants by hypovirulent Rhizoctonia spp. isolates is probably due to the combination of various protection modes, local and systemic, physical and induced in the plant. Therefore, the comprehensive reaction of protection which is achieved by the hypovirulent isolates could not be reconstructed by application of chemical substances in conventional pest control.

Scientific Publication
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