Agriculture Reference
In-Depth Information
and bacterial speck in North Carolina (Ivors & Louws, 2007) and in Florida (Olson &
Simonne, 2005).
The inclusion of ASM in tomato spray programmes may have additional benefi ts
since foliar applications of ASM have shown effi cacy against bacterial wilt (
Ralstonia
solanacearum
) (Anith
et al
., 2004; Pradhanang
et al.,
2005) and late blight (
Phytophthora
infestans
) (Becktell
et al.
, 2005). The effi cacy of ASM against bacterial wilt has been
shown to be affected by the inherent resistance of different tomato cultivars to the dis-
ease and also by the bacterial inoculum concentration. For example, ASM was effective
in 'Neptune', which exhibits moderate resistance to bacterial wilt, but not on the highly
susceptible 'Solar Set', when the treated plants were challenged with high bacterial
concentrations (10
7
CFU ml
1
). However, ASM controlled bacterial wilt on 'Solar Set'
when lower bacterial inoculum concentrations (10
5
CFU ml
1
) were used (Anith
et al.
,
2004; Hacisalihoglu
et al.,
2007).
At present, tomato spray programmes recommend the use of ASM in combination with
other fungicides and bactericides (Ivors & Louws, 2007) on the premise that ASM will
elevate host resistance whilst the other products will reduce pathogen inoculum levels. In
an effort to identify 'more sustainable' methods to reduce pathogen populations, research-
ers have investigated ASM in combination with microbial antagonists (Anith
et al.
, 2004;
Obradovic
et al.,
2004, 2005) and antimicrobial natural products (Ji
et al.,
2007). In stud-
ies on bacterial wilt, Anith
et al.
(2004) demonstrated that ASM, in combination with
two
Bacillus
strains
(BioYield™, Gustafson, LLC, Dallas), reduced disease incidence in
'Solar Set', whereas ASM alone did not. More recently, the integrated use of ASM in the
fi eld with thymol, applied as a preplant fumigant, reduced bacterial wilt incidence and
increased tomato yield (Ji
et al
., 2007). Furthermore, this combination treatment dem-
onstrated potential against root-knot nematode (
Meloidogyne
spp.) by causing a reduc-
tion in root galling and juvenile nematode populations. The authors propose that ASM/
thymol combinations may provide an alternative to methyl bromide for managing soil-
borne diseases.
Field and glasshouse studies on tomato bacterial spot demonstrated that applications
of ASM in combination with a bacteriophage formulation (Agriphage™, OmniLytics,
Inc., USA)
can
provide similar or better disease control than copper-mancozeb treat-
ments (Obradovic
et al
., 2004, 2005).
However
,
the
bacteriophage was inconsistent under
glasshouse conditions and showed limited survival under natural conditions when unfor-
mulated (Balogh
et al.,
2003). It has been proposed that formulated bacteriophage should
be applied at dusk for optimum effi cacy. In the same study, the integrated use of ASM
with antagonistic bacteria (
Bacillus pumilus
B122 and
Pseudomonas fl uorescens
B130)
did not offer any benefi t with respect to control of bacterial spot (Obradovic
et al.,
2005).
The integrated use of ASM in combination with reduced-risk insecticides and mulches
has been developed for management of tomato spotted wilt virus (Momol
et al.,
2004).
The authors reported that these strategies are being widely adopted by growers in north
Florida and South Georgia.
Induced resistance has also demonstrated effi cacy against fungal and oomycete patho-
gens in tomatoes. Grey mould, caused by
Botrytis cinerea,
is a continual threat to tomato
production and can infect leaves, stems, fl owers and fruit. In growth chamber experi-
ments, application of ASM retarded the development of
B. cinerea
lesions on
'Perkoz'
leaves (Malolepsza, 2006). Postharvest application of ASM protected 'Ciliegino' tomatoes
