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Onion rhizobacteria as potential plant health promotants


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Blackburn, Hannah Isobel 2001 , 'Onion rhizobacteria as potential plant health promotants', Research Master thesis, University of Tasmania.

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Sclerotium cepivorum Berk. (Berkeley, 1841), the causal agent of Allium White
Root Rot (AWRR) disease poses a major threat to the sustainability of the
Tasmanian onion industry, an export commodity which is worth $A40 million to
the state's economy. Tasmanian research into alternatives to fungicides for the
management of this disease has been primarily focussed on use of Trichoderma
spp. as fungal antagonists and novel bioactive substances such as diallyl
disulphides. In this study, antifungal bacteria from the onion rhizosphere were
examined for their potential as plant growth promotion agents with the view to
provide an additional component in the present integrated control strategy.
Bacteria isolated from root samples of healthy onions growing in an AVVRR
pathogen infested paddock were found to possess antifungal properties when
co-cultured in vitro with the pathogen at 10°C (typical of cropping soil
temperatures for onions in Tasmania). The five bacterial strains most active in S.
cepivorum inhibition were identified as members of the Enterobacteriaceae.
Molecular taxonomy studies indicated these were putatively novel species.
These isolates were screened in glasshouse trials with one isolate, M1RB2,
inducing production of significantly greater onion shoot biomass in dry warm
All bacteria trialled were suitable for formulation as a broadcast powder, and
exhibited high tolerance to Benlate, Thiram and Folicur, the three fungicides
most commonly used on Tasmanian onion crops. Studies on the impact of these
fungicides on native microbial populations showed that bacterial numbers may
be elevated by the application of a benlate-thiram seed dressing. These two
traits are of particular significance if a commercial product was to be developed.
ELISA surveys of the rhizosphere showed an increase in the proportion of
M6SA1-like bacteria in pots to which the bacteria had been introduced but no
significant change in total bacterial numbers.

Item Type: Thesis - Research Master
Authors/Creators:Blackburn, Hannah Isobel
Keywords: Onion industry, Sclerotium cepivorum, Onions
Copyright Holders: The Author
Copyright Information:

Copyright 2001 the Author. The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Agr.Sc.)--University of Tasmania, 2001. Includes bibliographical references

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