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Standardised production of aerobic compost extract for disease management in sustainable viticulture

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Palmer, AK (2009) Standardised production of aerobic compost extract for disease management in sustainable viticulture. PhD thesis, University of Tasmania.

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Abstract

Disease management in conventional viticulture involves regular applications of
synthetic fungicides. There is, however, significant pressure from grape and wine
markets to reduce inputs of synthetic fungicides because of concern about their
safety to humans and the environment, and due to increasing evidence of pathogen
populations developing fungicide resistance. Aerobic compost extract (ACE) is an
oxygenated watery extract of compost that favours the persistence of aerobic
microorganisms extracted from compost. Some horticultural practitioners claim that
ACE is a sustainable alternative to synthetic fungicides when applied to the soil or to
the fruit and foliage for crop protection. Scientific evidence supporting the
effectiveness and safety of ACE is limited. Moreover, wide variation in production
systems for ACE has made comparison of the few refereed reports available difficult.
The primary aim of this research was to standardise production of ACE for safety to
humans, and for consistent and high levels of suppression of two grapevine diseases
caused by fungal pathogens of different biology; namely, powdery mildew, caused
by Erysiphe necator, and botrytis bunch rot, caused by Botrytis cinerea.
Production variables for ACE from three composts with variable raw ingredients
were evaluated systematically by quantifying the growth and reproduction of B.
cinerea on detached bean leaflets treated with different ACEs. Bacterial-dominant
ACEs produced with a compost weight to water volume ratio of 1 :3 to 1: 10, and
from compost sampled in the very early secondary mesophilic stage of composting
inhibited B. cinerea colonisation of bean leaflets to a greater extent than ACEs
produced from compost sampled in the later mesophilic stages. There was evidence
to suggest that the magnitude of pathogen suppression was associated positively to
the number of bacterial and fungal Terminal Restriction Fragments (T-RFs) or microbial taxon diversity in ACE. This association will need to be tested further by
measuring T-RFs in ACEs prepared from a variety of compost windrows. ACE
directly inhibited the germination of B. cinerea conidia in vitro and removal of
microorganisms from ACE by filtration reduced but did not eliminate its capacity to
inhibit conidial germination. Water-soluble antibiotics were not detected in filtered
ACE following an in vitro assay for the inhibition of B. cinerea colony growth.
Under glasshouse conditions, the mean powdery mildew severity on Cabernet
Sauvignon leaves was less than 0.1 % when ACE was applied up to 4 days before or
up to 7 days after inoculation with E. necator conidia; mean severity on non-treated,
inoculated leaves was 22%. This result suggested that ACE had curative as well as
protective properties. ACE or ACE amended with fish hydrolysate and/or_liquid kelp
was prepared using standardised methods and applied nine or 12 times at 10-14 day
intervals to Chardonnay or Riesling vines grown commercially in different growing
seasons in southern Tasmania. Powdery mildew was controlled by ACE or amended
ACE to a commercially acceptable level on Chardonnay leaves and bunches under
conditions of high disease severity. The incidence of latent B. cinerea in Chardonnay
bunches at harvest, after moist incubation, was nearly half that observed in nontreated
bunches. The incidence and severity of sporulation of B. cinerea on Riesling
grape bunches was reduced significantly by ACE or amended ACE relative to a
dechlorinated water control treatment; these control bunches (not leaves) escaped
visible infection by E. necator but powdery mildew was controlled on leaves treated
with ACE or amended ACE. Treatment of Riesling leaves with ACE increased the
number of culturable microorganisms on leaves 100-fold, 1 h after application. By 13
days post-application the number of culturable microorganisms remained higher than
pre-application counts.
The human pathogenic bacteria Escherichia coli, Listeria monocytogenes and
Bacillus cereus were not detected in compost used to prepare standardised ACE.
Production conditions for ACE did not favour re-growth of a non-pathogenic
streptomycin resistant strain of E. coli. However, there was an increase in E. coli
numbers when fish hydrolysate or molasses were introduced to ACE. Further
experimental work is necessary to ensure negligible growth and persistence of human
pathogens in standardised ACE amended with nutrients. In the interim, standardised
ACE should be prepared without the addition of nutrients to prevent danger to human
health.
The effectiveness of standardised ACE can now be evaluated across _a range of
viticultural conditions and for its impact on grape and wine quality. It is envisaged
that ACE will be integrated with other measures to reduce the severity of diseases of
grapevines and other horticultural crops.

Item Type: Thesis (PhD)
Keywords: Viticulture, Grapes, Powdery mildew diseases, Botrytis cinerea
Copyright Holders: The Author
Copyright Information:

Copyright 2009 the author

Additional Information:

Available for use in the Library and copying in accordance with the Copyright Act 1968, as amended. Thesis (PhD)--University of Tasmania, 2009. Includes bibliographical references

Date Deposited: 03 Feb 2015 03:09
Last Modified: 11 Mar 2016 05:53
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