Sustainable agriculture and plant diseases: an epidemiological perspective

Abstract

The potential for modern biology to identify new sources for genetical, chemical and biological control of plant disease is remarkably high. Successful implementation of these methods within globally and locally changing agricultural environments demands new approaches to durable control. This, in turn, requires fusion of population genetics and epidemiology at a range of scales from the field to the landscape and even to continental deployment of control measures. It also requires an understanding of economic and social constraints that influence the deployment of control. Here I propose an epidemiological framework to model invasion, persistence and variability of epidemics that encompasses a wide range of scales and topologies through which disease spreads. By considering how to map control methods onto epidemiological parameters and variables, some new approaches towards optimizing the efficiency of control at the landscape scale are introduced. Epidemiological strategies to minimize the risks of failure of chemical and genetical control are presented and some consequences of heterogeneous selection pressures in time and space on the persistence and evolutionary changes of the pathogen population are discussed. Finally, some approaches towards embedding epidemiological models for the deployment of control in an economically plausible framework are presented.

Managing biotic interactions for ecological intensification of agroecosystems

“…Consequently, for ecological intensification, the substitution of large-scale chemical selective pressure by a large-scale biotic selective pressure, while avoiding problems of environmental pollution by chemical inputs, could lead to similar problems of pest adaptation. The likelihood that a pest will adapt to its natural enemy and escape the pest control process, which could result in an uncontrolled spread of a pest, is higher if the selective pressure is predictable in time and space (Gilligan, 2008). Including heterogeneity in selection pressures (both in intensity, time and space) could lower the persistence and adaptive potential of pathogens and pests (Gilligan, 2008;Rex Consortium, 2013).…”

“…The likelihood that a pest will adapt to its natural enemy and escape the pest control process, which could result in an uncontrolled spread of a pest, is higher if the selective pressure is predictable in time and space (Gilligan, 2008). Including heterogeneity in selection pressures (both in intensity, time and space) could lower the persistence and adaptive potential of pathogens and pests (Gilligan, 2008;Rex Consortium, 2013). The general idea would be to replace one strong selective pressure by several weaker selective pressures carefully distributed in time and space.…”

“…For example, pathogens could be controlled by weakening the transmission process of a disease by introducing gaps between susceptible and resistant hosts. One way might be to cultivate a mosaic of different crop species, some being susceptible, some being non-susceptible to the disease, or to apply biocides in a mosaic design (see Gilligan, 2008 for depicting the complexity of mechanisms involved in these strategies). An efficient management strategy should thus be drawn up over landscape and crop succession scales since the taxonomic, functional and genetic diversity of the crops are human-managed.…”

“…For management of agroecosystems based on spatio-temporal heterogeneity, the co-evolutionary process of resistance against the enemy and counter-resistance may lead to a mosaic of local adaptations (Thompson, 2005), creating de facto gaps in the distribution of pests susceptible and resistant to the enemy (e.g., asynchrony in fluctuations in resistance and susceptibility between demes Thrall et al, 2012). This might be a means of controlling the spread of diseases or pests, provided that the life-cycle and life history traits of both partners are known (e.g., dispersal ability Gilligan, 2008). For example, resource concentration techniques which are based on the dilution of the host plant in a crop mixture make a parasite or a pest less efficient in locating and colonizing its host plants (Ratnadass et al, 2012).…”

Evolution of an Invasive Species Research Program and Implications for Large-Scale Management of a Non-native, Invasive Plant Pathogen

“…To compare the 2010 RNA results against previous years' research priorities, we referenced "Sudden oak death: A 5-year Research Plan" (PSW, 2002), the 2007 RNA results (COMTF, 2007) and the 2008COMTF Nursery Committee Research Needs (COMTF, 2008b. These three documents provided lists of research questions that had been agreed upon and prioritized by various groups at the time.…”