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Microbial ecology of phytophthora cinnamomi suppressive soils : a study of biological suppression of P. cinnamomi in sub-tropical avocado orchards on the east coast of Australia.
Author/Creator:
Keen, Bradley Paul,
University of Western Sydney,
College of Health and Science,
School of Natural Sciences
Date: 2006
Subject:
Phytophthora cinnamomi control,
suppressive soils,
avocado orchard soils,
Australia
Record contributed by: Australasian Digital Theses Program, University of Western Sydney
Full Record and related resources:
http://handle.uws.edu.au:8081/1959.7/16038
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http://handle.uws.edu.au:8081/1959.7/16038
Description
This study focuses on the soil- and water-borne plant pathogen Phytophthora cinnamomi Rands and the phenomenon of P. cinnamomi suppressive soil. In particular, this thesis reports on the outcome of field surveys and glasshouse assays undertaken to locate P. cinnamomi suppressive soils and to confirm the involvement of biological processes in suppression. The potential role of cellulase and laminarinase in suppression was investigated and a molecular technique known as length heterogeneity PCR (LH-PCR) was used to analyse the structure and diversity of bacterial and fungal communities in avocado orchard soils that were suppressive and conducive to P. cinnamomi. Four avocado orchards with P. cinnamomi suppressive soils were identified and soils were ã-irradiated to destroy their suppressive capacity, thus confirming biological suppression. Suppression was also partially transferred to ã-irradiated and conducive soils by mixing with 10% suppressive avocado soils. Cellulase and laminarinase activities measured in avocado orchard soils inoculated with P. cinnamomi were not associated with disease severity in lupin seedlings during glasshouse assays involving the same soil samples. Minor shifts in bacterial and fungal community structure were observed in response to mixing conducive and irradiated soils with suppressive soils. This was associated with decreased disease severity in avocado seedlings in these treatments. The shift in bacterial community structure was partially determined by the appearance and increased abundance of several bacterial 16S rDNA sequences, which were unique to the suppressive soils, in the mixed soil treatments. It is suggested that the bacteria and fungi from which these sequences originated may be involved in suppression and further work should be undertaken to determine their identity and confirm their potential role in the development and maintenance of P. cinnamomi suppressive soils.
Doctor of Philosophy (PhD)
Language: eng
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This study focuses on the soil- and water-borne plant pathogen Phytophthora cinnamomi Rands and the phenomenon of P. cinnamomi suppressive soil. In particular, this thesis reports on the outcome of field surveys and glasshouse assays undertaken to locate P. ...
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Seasonal effects of foliar application of phosphonate on phosphonate translocation, in vitro pollen viability and pollen germination in `Hass' avocado (Persea americana Mill.)
Author/Creator:
Nartvaranant, P.,
Hamill, S.,
Leonard, J.,
Whiley, A.W.
Resource type: journal article
Date: 2004
Subject:
History
Record contributed by: Queensland Department of Employment, Economic Development and Innovation eResearch Archive
Full Record and related resources:
http://era.deedi.qld.gov.au/699/
http://era.deedi.qld.gov.au/699/
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http://era.deedi.qld.gov.au/699/
http://era.deedi.qld.gov.au/699/
Description
Phosphonate fungicides are used widely in the control of diseases caused by Phytophthora cinnamomi Rands. For the most part phosphonate is seen as a safe to use on crops with phytotoxicity rare. However, recent research has shown that phosphonate has detrimental effects on the floral biology of some indigenous Australian plants. Since phosphonate fungicides are regularly used for the control of Phytophthora root rot in avocados, research was carried out to study the translocation of phosphonate fungicide in `Hass' trees and any effects on their floral biology. Field- grown trees were sprayed with 0, 0.06 or 0.12 M mono-dipotassium phosphonate (pH 7.2) at summer flush maturity, floral bud break or anthesis. Following treatment, phosphonic acid concentrations were determined in leaves, roots, inflorescence rachi and flowers and in vitro pollen germination and pollen tube growth studied. Phosphonic acid concentration in the roots and floral parts was related to their sink strength at the respective times of application with concentration in roots highest (36.9.mg g±1) after treatment at summer flush maturity and in flowers (234.7 mg g±1) after treatment during early anthesis. Phosphonate at >0.03 M was found to be significantly phytotoxic to in vitro pollen germination and pollen tube growth. However, this rate gave a concentration far in excess of that measured in plant tissues following standard commercial applications of mono-dipotassium phosphonate fungicide. There was a small effect on pollen germination and pollen tube growth when 0.06 and 0.12 M mono-dipotassium phosphonate was applied during early anthesis. However, under favourable pollination and fruit set conditions it is not expected to have commercial impact on tree yield. However, there may be detrimental commercial implications from phosphonate sprays at early anthesis if unfavourable climatic conditions for pollination and fruit set subsequently occur. A commercial implication from this study is that phosphonic acid root concentrations can be elevated and maintained with strategic foliar applications of phosphonate fungicide timed to coincide with peaks in root sink strength. These occur at the end of the spring and summer flushes when shoot growth is relatively quiescent. Additional foliar applications may be advantageous in under high disease-pressure situations but where possible should be timed to minimize overlap with other signifcant growth events in the tree such as rapid inflorescence, and fruit development and major vegetative flushing.
Publisher: The Journal of Horticultural Science & Biotechnology Trustees
Other identifier: Nartvaranant, P. and Hamill, S. and Leonard, J. and Whiley, A.W. (2004) Seasonal effects of foliar application of phosphonate on phosphonate translocation, in vitro pollen viability and pollen germination in `Hass' avocado (Persea americana Mill.). Journal of Horticultural Science & Biotechnology, 79 (1). pp. 91-96.
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Phosphonate fungicides are used widely in the control of diseases caused by Phytophthora cinnamomi Rands. For the most part phosphonate is seen as a safe to use on crops with phytotoxicity rare. However, recent research has shown that phosphonate has detrimental ...
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Tree vigour influences disease susceptibility of 'Hass' avocado fruits
Author/Creator:
Willingham, S.L.,
Coates, L.M.,
Cooke, A.W.,
Dean, J.R.
Resource type: journal article
Date: 2004
Subject:
Pests and diseases,
Fruit and fruit culture
Record contributed by: Queensland Department of Employment, Economic Development and Innovation eResearch Archive
Full Record and related resources:
http://era.deedi.qld.gov.au/305/
http://era.deedi.qld.gov.au/305/1/Willingham_tree.pdf
http://dx.doi.org/10.1071/AP03079
http://era.deedi.qld.gov.au/305/
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http://era.deedi.qld.gov.au/305/
http://era.deedi.qld.gov.au/305/1/Willingham_tree.pdf
http://dx.doi.org/10.1071/AP03079
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Description
Differences in tree vigour as a result of feeder root destruction by Phytophthora cinnamomi were found to significantly (P < 0.05) influence disease susceptibility, fruit ripening rates and fruit size of 'Hass' avocado. Fruits from root rot-affected, non-vigorous trees had less anthracnose and took longer to ripen. However, they were probably unmarketable due to their small fruit size compared with fruits from healthy vigorous trees. Fruits from non-vigorous trees also had less pepper spot than vigorous trees, but only on the inside of the tree canopy. The increased disease resistance of fruits from non-vigorous trees was related to a 40% increase in the concentration of Ca in the fruit flesh.
Publisher: CSIRO Publishing
Format: application/pdf
Other identifier: Willingham, S.L. and Coates, L.M. and Cooke, A.W. and Dean, J.R. (2004) Tree vigour influences disease susceptibility of 'Hass' avocado fruits. Australasian Plant Pathology, 33 (1). pp. 17-21.
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Differences in tree vigour as a result of feeder root destruction by Phytophthora cinnamomi were found to significantly (P < 0.05) influence disease susceptibility, fruit ripening rates and fruit size of 'Hass' avocado. Fruits from root rot-affected, non-vigorous ...
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Selection for decreased sensitivity to phosphite in Phytophthora cinnamomi with prolonged use of fungicide
Author/Creator:
Dobrowolski, M.P.,
Shearer, B.L.,
Colquhoun, I.J.,
O’Brien, P.A.,
Hardy, G.E.St.J.
Resource type: Journal Article
Date: 2008
Subject: No Subjects
Record contributed by: Murdoch University
Full Record and related resources:
http://researchrepository.murdoch.edu.au/2327/
http://researchrepository.murdoch.edu.au/2327/
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http://researchrepository.murdoch.edu.au/2327/
http://researchrepository.murdoch.edu.au/2327/
Description
To test the hypothesis that resistance in Phytophthora cinnamomi to control by the fungicide phosphite (phosphonate) would arise in sites with prolonged use of phosphite, 30 P. cinnamomi isolates were collected from a range of sites with different phosphite-use histories, including phosphite-treated and untreated avocado orchards, and phosphite-treated and untreated native vegetation sites. The colonizing ability of these isolates was tested by different inoculation methods against a range of host tissues, treated and untreated with phosphite, including mycelial stem inoculation on clonally propagated Leucadendron sp., mycelial root inoculation of lupin seedlings and zoospore inoculation of Eucalyptus sieberi cotyledons. Isolates from avocado orchards with a long history of phosphite use were, on average, more extensive colonizers of the phosphite-treated Leucadendron sp., lupin seedling roots and Eucalyptus sieberi cotyledons. These isolates did not colonize untreated plant tissue (Leucadendron sp.) more extensively than isolates from sites with no history of phosphite use and no isolates were resistant to control by phosphite. Analysis of all isolates with microsatellite markers revealed the majority were from a single clonal lineage. Selection for decreased sensitivity to phosphite in planta has taken place within asexual clonal lineages of P. cinnamomi in sites with prolonged use of phosphite.
Publisher: Wiley-Blackwell
Language: eng
Source: Dobrowolski, M.P. , Shearer, B.L. , Colquhoun, I.J., OâBrien, P.A. and Hardy, G.E.St.J. (2008) Selection for decreased sensitivity to phosphite in Phytophthora cinnamomi with prolonged use of fungicide. Plant Pathology, 57 (5). pp. 928-936.
Rights: © 2008 The Authors.
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To test the hypothesis that resistance in Phytophthora cinnamomi to control by the fungicide phosphite (phosphonate) would arise in sites with prolonged use of phosphite, 30 P. cinnamomi isolates were collected from a range of sites with different phosphite-use ...
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