Modelling the dynamics of a plant pathogen and a biological control agent in relation to flowering pattern and populations present on leaves

A flexible model for biological control of a plant pathogen affecting host flowers is developed which takes into account the transfer of both the plant pathogen and the biological control agent (BCA) from the leaves to flowers. Because flowers, other than in ornamental plants, are largely ephemeral, the emphasis in analysis is on the rates of transfer and establishment on flowers. The form of the model analysed depends upon: the pattern of flowering for a particular host plant, a single instantaneous flush or continuous seasonal production; the effect of flowering phenology and morphology on transfer of both the pathogen and BCA; and the transient dynamics of such transfer. In the case of a single instantaneous flush, the relative importance of mycoparasitism and competition in protecting flowers during their short period of blooming is assessed. Where flowering is continuous but transfer lags behind because of floral phenology or morphology, a comparison is made between the initial levels of the pathogen and the BCA as they transfer to the flowers, depending again on the relative contribution of mycoparasitism and competition over the extended period of blooming. Differential rates of transfer of the pathogen and the BCA, depending on their time-dependent population densities on leaves, have a major impact on eventual biocontrol outcomes. The model results are used to analyse biocontrol strategies for contrasting host-pathogen systems which show different flowering patterns and biological control mechanisms. For Erwinia amylovora causing fireblight in pome fruit trees, an inundative biocontrol strategy targeting flowers is supported. In Botrytis cinerea, there is considerable potential for a strategy based on the establishment of BCAs on leaves for some of the plant hosts affected.