Author:
Kirkegaard J. A.,Sarwar M.,Wong P. T. W.,Mead A.,Howe G.,Newell M.
Abstract
Biofumigation refers to the suppression of soil-borne pathogens and pests by
biocidal compounds released by Brassica crops when
glucosinolates (GSL) in their residues decay in soil. We conducted field
studies at 2 sites to investigate the hypothesis that biofumigation by
Brassica break crops would reduce inoculum of the
take-all fungus Gaeumannomyces graminis var.
tritici (Ggt) to lower levels than
non-Brassica break crops, and thereby reduce Ggt
infection and associated yield loss in subsequent wheat crops. High and
uniform levels of Ggt were established at the sites in the first year of the
experiments by sowing wheat with sterilised ryegrass seed infested with Ggt.
Ggt inoculum declined more rapidly under Brassica crops
than under linola and this reduction coincided with the period of root decay
and reduced root glucosinolate concentrations around crop maturity. There was
no consistent difference in inoculum reduction between canola
(Brassica napus) and Indian mustard
(Brassica juncea), nor between cultivars with high and
low root GSL within each species. Despite significant inoculum reduction
attributable to biofumigation, there were no differences in the expression of
disease and associated impacts on the yield of subsequent wheat crops across
the sites. Seasonal conditions, in particular the distribution of rainfall in
both the summer–autumn fallow following the break crops and during the
subsequent wheat crop, influenced inoculum survival and subsequent disease
development. In wet summers, inoculum declined to low levels following all
break crops and no extra benefit from biofumigation was evident. In dry
summers the lower inoculum levels following brassicas persisted until the
following wheat crops were sown but subsequent development of the disease was
influenced more by seasonal conditions than by initial inoculum levels.
Significant extra benefits of biofumigation were observed in one experiment
where wheat was sown within the break crops to simulate grass weed hosts of
Ggt. Under these circumstances there was greater reduction in Ggt inoculum
under canola than linseed and an associated decrease in disease development.
For host-dependent pathogens such as Ggt, we hypothesise that the benefits of
biofumigation to subsequent wheat crops will therefore be restricted to
specific circumstances in which inoculum is preserved during and after the
break crops (i.e. dry conditions, grass hosts present) and where conditions in
the following wheat crop lead to significant disease development (early
sowing, wet autumn and spring, dry periods during grain filling).
Subject
General Agricultural and Biological Sciences
Cited by
90 articles.
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