Induced resistance for plant disease control - Disease Control in Crops - page 75

4.2.1.13 Cotton

Mondal et al . (2005) reported that ASM seed treatment could reduce the severity of black
root rot disease ( Thielaviopsis basicola ) in cotton seedlings raised in soils that were natu-
rally infested with the pathogen. Soaking cotton seed in ASM for 3 hours before sow-
ing resulted in a 33% reduction in black root rot severity on tap roots. Disease severity
was reduced by 20% and 24%, respectively, when ASM was applied as a seed dressing
or as an in-furrow spray during sowing. Foliar application of ASM was, however, not
effective and this may be because infection was established before treatment application.
Nevertheless, the authors suggested that ASM seed treatment could provide an important
component of an integrated management approach. Syngenta Crop Protection (Australia)
have recently registered Bion ® (a.i. ASM) as a seed treatment in Australia for the man-
agement of fusarium wilt ( F. oxysporum f. sp. vasinfectum ) and black root rot in cotton
(http://www.syngenta.com.au/start.aspx). In trials, Bion ® has reportedly decreased both
the incidence of fusarium wilt by up to 42% and severity of black root rot by up to 50%.

4.2.2 Ornamentals

Cut fl owers are a highly perishable commodity crop that relies on low temperature and
high humidity to retard fl ower senescence during transportation to market. Unfortunately,
these conditions may encourage the development of infections by fungal pathogens
like B. cinerea, the most problematical postharvest pathogen to the cut-fl ower industry
(Ngugi & Scherm, 2006). Infection commonly occurs during fl ower development but
then remains symptomless until after harvest. Geraldton waxfl ower, an important export
cut-fl ower crop in Australia, is susceptible to postharvest fl oral abscission caused by
B. cinerea infection. Postharvest MeJA vapour treatment (1100 l MeJA/L) of 'Purple
Pride' and 'Mullering Brook' waxfl ower sprigs reduce the severity of natural Botrytis
infections on fl owers but did not control infections on 'artifi cially' inoculated fl owers
(Eyre et al., 2006). Arguably, of greater concern was the observation that MeJA treat-
ment induced increased fl oral organ abscission in 'Purple Pride' and 'Mullering Brook'
after 48 days. In fi eld experiments, application of MeJA (500750 M), three days
before harvest, slightly reduced postharvest Botrytis severity on 'My Sweet Sixteen' but
not on 'Mullering Brook' (Dinh et al., 2007). In the same study, applications of ASM
(50150 mg l 1 ) and silicon (0.51.5 g l 1 ) had no effect on disease severity or fl oral
abscission. More recently, Dinh et al . (2008) investigated multiple MeJA applications
as well as MeJA/ASM and MeJA/silicon combinations against Botrytis in Geraldton
waxfl ower. The only treatment that consistently reduced Botrytis incidence and severity
was application of MeJA (1 mM), 3 days before harvest, followed by a second MeJA
(0.51 mM) application within 26 hours of harvest. However, despite the reduction in
disease incidence, the reduction of pathogen-induced fl oral abscission was considered too
small to be of any practical value.
Cut freesias are frequently rejected because of visible lesions on fl ower petals (petal
specking) caused by B. cinerea infections. MeJA and ASM have been evaluated as
preharvest and as postharvest treatments to protect freesias against petal specking
(Darras et al. , 2005, 2006, 2007). Preharvest sprays of MeJA (0.20.6 mM) and ASM
(1.435.71 mM), applied weekly from 28 days before harvest, afforded protection against