Industry Representative: Richard Pett, JEPCO (Marketing) Ltd.
AHDB Horticulture Cost: £68,577.00
Summary: With the reducing number of fungicides available to manage diseases, there is even more pressure to identify effective alternatives for integrated disease management. Only a few products based on microbial biocontrol agents (BCA) have been registered in the UK to control fungal diseases, primarily Botrytis cinerea. These BCAs have been usually applied as if they were fungicides and their efficacy is often variable. Recent theoretical modelling suggested that understanding BCA population dynamics in relation to climatic conditions is critical for their deployment to control foliar pathogens. However, this aspect of biocontrol research has so far been neglected.
Aims and Objectives:
Objective 1: Developing methods for quantifying BCA population sizes (by month 12)
Cytological quantification. For B. subtilus, we shall try to genetically transform the isolates with the GFP gene to facilitate direct quantification of this BCA under the microscope. This technique has been used in many pathological studies to understand infection and subsequent invasion of pathogens inside host tissues by visualising the organisms in question. An important question is to ensure that the transformed isolate has the same or similar ecological requirements.
Plating technique. For all three BCAs, plating techniques will be used to directly estimate the amount of viable colony forming units (CFU) on agar media. This approach depends on whether there are sufficient unique colony characteristics for each BCA strain to distinguish them from other resident microflora.
Indirect estimation. If neither the cytological nor the plating method has worked for one or more BCA, an indirect method will be used to estimate CFU based on Botrytis severity on treated leaves. This method assumes that BCA population size is monotonically related to disease control efficacy.
Temperature and humidity will be studied for their effects on BCA dynamics. Experimental protocols will depend on how BCA propagule density is quantified (WP1). Experiments will be conducted initially in controlled conditions where temperature and humidity (including rainfall) are controlled and later in semi-commercial conditions (glasshouse and/or open field). These experiments are conducted to answer the following questions:
• To what extent are BCA propagules dispersed to newly emerged plant tissues? This will determine whether (and if so, at what frequency) repeated application of BCAs is necessary.
Initial experiments will be conducted under controlled conditions to study combined use of BCAs in relation to synergy and the variability in biocontrol efficacy. Each product will be applied either alone or in combination with another. Disease development will be assessed at several time points. Later, similar experiments will be conducted on commercial crops with multiple applications of BCAs. Results from these experiments will answer the following questions:
• What combinations of BCAs can result in synergy or independent interaction? This will enable selections of BCAs to improve efficacy.
• Could combined use of BCAs lead to reduced variability in biocontrol efficacy? This is important for assessing biocontrol potentials of individual products. Inconsistency in biocontrol among different studies is one factor limiting the use of BCAs.
Recently we developed a model to evaluate biocontrol with one or two BCAs under fluctuating conditions. We shall use the data obtained in WP2 to estimate BCA-related model parameters. We also attempt to incorporate fungicide effects into the model in order to evaluate the efficacy of joint use of fungicides and BCAs. Strategies will be compared theoretically using models and experimentally in large field experiments, including use of individual BCAs, combined use of BCAs at the same time, and use of alternative BCAs over time. Data from field and modelling studies will answer the following questions:
• How often does combined use of BCAs outperform individual BCAs based on modelling studies using historical weather data recorded over a period of 90 years at East Malling?
• Does one strategy consistently outperform another one in terms of disease suppression and variability in disease suppression?
• Does the performance of a particular strategy depend on particular crops (strawberry and lettuce) or BCAs?
Answers to these questions form the foundation of optimising strategies of applying BCAs in practice.