Agriculture Reference
In-Depth Information
Integrated pest management is a cornerstone of fl oriculture (Daughtrey & Benson,
2005)
and it is likely that activators will have a role to play in disease management by
the ornamentals industry in the future. However, the problem of variable effi cacy must
be overcome before the industry will consider their practical implementation. For a more
comprehensive review on the use of activators to manage postharvest disease in cut fl ow-
ers, see Dinh & Joyce (2007).
4.2.3
Forestry
Induced resistance may have potential to contribute to disease management in forest
nurseries (Reglinski & Dick, 2005). Foliar application of SA and 5-chlorosalicylic acid
protected
Pinus radiata
seedlings against wound infection by
Sphaeropsis sapinea
for
up to 32 days (Reglinski
et al.,
1998). Interestingly, SA applications increased the bio-
mass of
Pinus patula
seedlings, a trait that may aid establishment of young seedlings in
plantation sites (San-Miguel
et al
., 2003).
Banksia attenuata
seedlings expressed ele-
vated resistance to
stem inoculation with
Phytophthora cinnamomi
one week after treat-
ment with 0.5 mM benzoic acid, applied either as a soil drench or foliar spray (Williams
et al.,
2003).
Phytophthora cinnamomi
is also commonly shown to cause root rot in
conifers. Phosphorous acid derivatives, also referred to as phosphonate or phosphite,
have been shown to provide effective control of
Phytophthora-
related diseases in several
plant species (Hardy
et al.,
2001). These compounds exhibit direct antifungal activity
and can activate host resistance against infection (Guest & Grant, 1991). Application of
potassium phosphonate (Foli-R-Fos 200™, UIM Agrochemicals) caused a reduction in
P. cinnamomi
root rot in glasshouse-grown
P. radiata, Banksia integrifolia
and
Isopon
cuneatus
(Ali
et al.
, 2000). Suppression of root rot was further enhanced when potassium
phosphonate was sprayed in combination with ASM. All untreated seedlings died within
14 weeks of inoculation with
P. cinnamomi
,
whereas all treated plants remained alive.
Phosphite has also been shown to reduced infections caused by
P. cinnamomi
in mature
Banksia
sp. and
Eucalyptus marginata
trees when applied by trunk injection (Shearer &
Fairman, 2007).
MeJA readily volatilises and is known to function as an airborne chemical sig-
nal among plants. Young Norway spruce seedlings were more resistant to infection by
P. ultimum
after exposure to gaseous MeJA (Kozlowski
et al.,
1999). Mortality was
reduced from 80% to 40% in seedlings that were exposed to 26 ppb MeJA for 3 days.
Application to the bark of 30-year-old Norway spruce enhanced resin fl ow and induced
resistance to inoculation with the blue stain fungus
Ceratocystis polonica
(Franceschi
et al.
, 2002). Induced resistance was expressed as a 50% reduction in lesion length in
treated trees. More recently, radiata pine seedlings exhibited elevated resistance to wound
infection by
S. sapinea
following
one single foliar application of 4.5 mM MeJA (Gould
et al.
, 2008). The induced resistance response was accompanied by a concomitant reduc-
tion in seedling growth rate which the authors attributed to reallocation of resources
towards active defence mechanisms.
Plant-growth-promoting rhizobacteria (PGPR), particularly
Bacillus
spp., and
Pseudomonas
spp., have been shown to enhance the rate and amount of seedling emer-
gence, and also to stimulate seedling growth in conifers (Chanway, 1997; Enebak
et al
.,
1998). PGPR also have potential as biocontrol agents and have been shown to suppress
