Abstract:
For sustainable agriculture, efficient usage of biocontrol agents (BCAs) is crucial. As
BCAs are living organisms effective biocontrol ability is governed by complex
ecological processes. Because of this, biocontrol of plant diseases can become
constrained. Research on the ecology, mechanisms of action and population ecology
in the phyllopshere environment is critical for modelling the efficacy of BCAs for
control of foliar plant pathogens, especially Botrytis cinerea. The aim of the research
was to obtain ecological knowledge on Bacillus subtilis QST 713 and Gliocladium
catenulatum J1446, and if feasible use this ecological information to apply these two
BCAs against B. cinerea. Thus the objective initially was to (i) develop a molecular
based assay to quantify viable population changes of the two BCAs, and use this
novel assay for investigating: (ii) the dose response relationship of B. cinerea to the
bacterial and fungal BCA, (iii) impact of relative humidity (RH) and temperature used
in UK agronomic production systems on BCA populations, (iv) produce a simple
model to predict BCA fate, (v) identify the colonisation and dispersion kinetics of the
two BCAs on expanding foliage, and finally from the collected ecological knowledge
(vi) suggest optimisations strategies for the two BCAs. This study successfully
developed a PMAxxᵀᴹ-qPCR method for quantifying the kinetics of viable population
changes for both the BCAs. The dose response relationship of B. cinerea to the
BCAs’ was deciphered and G. catenulatum median effective dose was 1 × 10⁸
spores/ml, while for B. subtilis this was 3 × 10⁸ CFUs/ml⁻¹
. However, this changed
with temperature, formulation, and leaf tissue type. Both temperature and humidity
impacted on viable population dynamics of the two BCAs, and showed that viable
populations were sustained, increased or reduced depending on abiotic factors
(temperature, R.H.), with efficacy best at conditions close to the BCAs optimum
growth conditions. From the collected data, models were produced and tested for
their ability to predict the fate of each BCA in commercial growing sites. The
dispersion and colonisation kinetics of the two BCAs were analysed on growing
lettuce and strawberry leaves. The two BCAs behaved in different ways, while their
ability to disperse and colonise virgin leaf tissue was effective, the rate depended on
the season (temperature and RH) and host. This study has developed significant
new ecological knowledge on these two BCAs and their behaviour when applied to
strawberry and lettuce leaf surfaces, and their establishment to control B. cinerea in
these agronomic crop systems.
