Agriculture Reference
In-Depth Information
as a food source. The phenomenon is of particular pertinence to biofumigation because
of the known susceptibility of the synthetic compound methyl ITC (Matthiessen
et al
.,
2004) and the recent demonstration of cross-degradation - the ability of the same organ-
isms to rapidly degrade a range of other ITCs from plant sources (Warton
et al
., 2003).
Matthiessen & Kirkegaard (2006) discuss the implications of this in detail and raise
several pertinent points. Firstly, as methyl bromide is not susceptible to this phenomenon,
any replacement strategy involving either synthetic or plant-based ITC will be susceptible
and this should be managed. Secondly, biofumigation may be ineffective as an alternative
disease control strategy on soils which have already developed enhanced biodegradation
to synthetic methyl ITC due to cross-degradation. Thirdly, and without specifi c data, they
speculate that the likelihood of developing enhanced biodegradation using biofumigation
would be signifi cantly less than using high doses of pure compounds due to the array of
other compounds.
9.8
Field implementation
Disease suppression using ITC-based biofumigation can be maximized using implemen-
tation strategies based on the fundamental aspects of ITC formation, release and activity
in soils and the attributes of the target organism outlined in the previous sections. The
extent to which the variability in suppression levels previously reported can be ascribed
to the failure to adopt such approaches cannot be known, but the obvious involvement
of mechanisms other than ITC-related biofumigation emphasize the need to consider
biofumigation in an IPM context, as part of an overall disease control strategy. Strategies
for success, opportunities for integrated approaches and some specifi c case studies are
used to exemplify this in the following sections.
9.8.1
Strategies to maximize ITC-related biofumigation
Several general guidelines to improve the effi cacy of ITC-based disease control can be
proposed based on the principles outlined in previous sections as well as the review of the
results from published fi eld experiments (Matthiessen & Kirkegaard, 2006).
(a) Establish a correlation between GSLs, ITCs and pest suppression
Pursuing ITC-related biofumigation as a component of disease control may be pointless if
there is no clear link between GSL content of the tissue, the ITC released from the tissue
and the level of pest suppression. Such relationships have often been investigated
in vitro
using pure compounds, rehydrated or macerated tissue. The numerous impacts of soil on
ITC activity suggest some indication of this link in a soil-based assay would be valuable
prior to expensive fi eld studies. Experience also suggests some pathogens (e.g.
Pythium
)
are less sensitive to ITCs and can proliferate on incorporated organic material and are
therefore unlikely targets for success with biofumigation.
(b) Select an appropriate biofumigant for the farming system
Select a biofumigant that produces large quantities of GSLs known to release ITCs most
toxic to the target organism (preferably demonstrated in soil) in the time available for its
growth.
Brassica
species high in short-chained aliphatic ITCs such as 2-propenyl ITC
