Agriculture Reference
In-Depth Information
Fig. 9.2
Detached bean leaf-
lets with (
a
) droplets of a sus-
pension of
Botrytis cinerea
conidia prior to incubation,
and (
b
) necrotic lesions after
inoculation with
B. cinerea
and incubation of sealed
plates for 5 days in darkness
at 21 ± 4 °C. Reproduced from
Palmer et al. (
2010b
)
microorganisms with unknown metabolic activity. In short, pathogen growth inhibi-
tion in vitro may be a consequence of the selection pressure exerted by the growth
medium, and it may or may not be an indicator of the potential for disease suppres-
sion involving other substrates and environmental conditions.
When the goal is to investigate disease suppressiveness of a compost tea di-
rectly, then one approach is to select a model pathosystem amenable to rapid and
reproducible bioassay.
B. cinerea
is a suitable fungal pathogen for initial testing of
compost tea because it is common in the environment and colonises a wide range
of fruit, vegetable and ornamental crops in many different climates (Coley-Smith
et al.
1980
). The necrotrophic mode of nutrition of
B. cinerea
means that it gener-
ally colonises senescing plant tissues and can alternate between being a saprobe and
plant pathogen. Important diseases of flowers and fruit caused by
B. cinerea
include
bunch rot of wine and table grapes and grey mould of strawberries. Palmer et al.
(
2010b
) described a method for single-point inoculation of detached bean leaflets
(Fig.
9.2
) whereby the area or dimensions of the resulting discrete lesions are mea-
sured readily by image analysis.
If the plant pathogen of interest is an obligate biotroph, such as a mildew or rust
fungus, then glasshouse trials involving inoculation and treatment of whole plants
can provide information under conditions that are ideal for both host and pathogen
growth. These trials are also useful for studying whether or not a single applica-
tion of compost tea can eradicate young mildew colonies or infections established
within 24-72 h of inoculation. The effect of the period between treatment with
compost tea and pathogen inoculation on the level of disease suppression can also
be investigated, along with relevant methodology to investigate the potential of
compost tea to induce disease resistance in the host plant.
9.7.2
Field Trials
The European and Mediterranean Plant Protection Organization (EPPO) publishes
general and specific standards for plant pathogens or pathosystems with regard
to the conduct of field trials to evaluate the efficacy of plant protection products
(Anonymous
2013
). Field trials are often conducted in replicated small plots using a
randomised complete-block design amenable to analysis of variance. These designs
