Agriculture Reference
In-Depth Information
proliferation when low-GSL rapeseed meal was applied could be accomplished using a
soil drench of mefenoxam, and the combination of the rapeseed meal and the chemical
drench could reduce disease symptoms to the same extent as fumigation (Mazzola &
Mullinix, 2005). Another approach under investigation involves utilization of mixes com-
prising mustard (
Brassica juncea
) and rapeseed meal as the principal ITC released from
mustard (2-propenyl ITC) has been shown to have greater activity against
Pythium
spp.
(Cohen & Mazzola, 2006). This series of studies exemplify the complexity of mechanisms
which can be involved in disease control using Brassicaceous amendments. However, it
also serves to highlight how careful experimentation with appropriate controls to sepa-
rate the GSL and non-GSL related mechanisms of disease control operating in disease
suppression can lead to integrated approaches which may combine Brassicaceous
amendments with other strategies to provide commercially viable control.
9.9
Further development of biofumigation as a disease management tool will require research
within a systematic framework taking account of many factors from the fundamental soil
and plant processes, to the practicalities of specifi c farming systems. The most recent
research and development fi ndings summarized in this chapter suggest there may now be
impetus for self-sustaining further development and market penetration of the concept.
However there needs to be appropriate targeting and realistic expectations of the concept as
a component of a disease management system. Biofumigation is not suffi ciently powerful
or practical in implementation to replace synthetic fumigants and such misdirection would
be counterproductive. It has been demonstrated to have effi cacy, secondary soil benefi ts
and, notably economic benefi ts in an appropriate production system that traditionally uses
metham sodium, and uptake in at least one regional production system has been high
(McGuire, 2004). Successful future implementation could arise from current research in
several areas. There appears to be signifi cant scope to improve the effectiveness of ITC-
related suppression by purposeful selection or development of varieties with very high
concentrations of the relevant GSL, and by using incorporation techniques which maxi-
mize the release effi ciency and residence time of ITCs in soil. Understanding the fate of
both the GSLs and the hydrolysis products in soil is required to minimize environmental
consequences, a key aim of non-chemical approaches. Much of the necessary soil and plant
data relevant to these processes has been notably absent from many previous studies on
disease control using biofumigation. The non-specifi c biocidal nature of ITCs combined
with the signifi cant non-ITC related changes in microbial profi les increasingly reported
following biofumigation demands a more thorough understanding of the overall changes
in the soil biology generated by biofumigants. New DNA-based soil microbial profi ling
approaches such as DDGE, RISA, T-RFLP and utilization of specifi c PCR primers offer
new opportunities to understand both the specifi c and general changes in the soil microbial
ecology which can infl uence disease expression. This understanding is essential particu-
larly where biofumigation is combined with other biological approaches so that synergis-
tic rather than antagonistic processes are encouraged using these integrated approaches.
Without this understanding, biofumigation, along with other biological approaches, will
be consigned to the list of promising but inconsistent cultural control options which cannot
offer the reliable effi cacy of the existing chemical options they seek to replace.
Summary
