A framework to gauge the epidemic potential of plant pathogens in environmental reservoirs: the example of kiwifruit canker

Abstract

New economically important diseases on crops and forest trees emerge recurrently. An understanding of where new pathogenic lines come from and how they evolve is fundamental for the deployment of accurate surveillance methods. We used kiwifruit bacterial canker as a model to assess the importance of potential reservoirs of new pathogenic lineages. The current kiwifruit canker epidemic is at least the fourth outbreak of the disease on kiwifruit caused by Pseudomonas syringae in the mere 50 years in which this crop has been cultivated worldwide, with each outbreak being caused by different genetic lines of the bacterium. Here, we ask whether strains in natural (non-agricultural) environments could cause future epidemics of canker on kiwifruit. To answer this question, we evaluated the pathogenicity, endophytic colonization capacity and competitiveness on kiwifruit of P. syringae strains genetically similar to epidemic strains and originally isolated from aquatic and subalpine habitats. All environmental strains possessing an operon involved in the degradation of aromatic compounds via the catechol pathway grew endophytically and caused symptoms in kiwifruit vascular tissue. Environmental and epidemic strains showed a wide host range, revealing their potential as future pathogens of a variety of hosts. Environmental strains co-existed endophytically with CFBP 7286, an epidemic strain, and shared about 20 virulence genes, but were missing six virulence genes found in all epidemic strains. By identifying the specific gene content in genetic backgrounds similar to known epidemic strains, we developed criteria to assess the epidemic potential and to survey for such strains as a means of forecasting and managing disease emergence.

Eight principles of integrated pest management

“…There are other plant pathogens characterized by broad host range that need to be treated differently, however. Such is the case of the bacteria Pseudomonas syringae (Bartoli et al 2014;Lamichhane et al 2014a) and Xanthomonas arboricola (Lamichhane 2014) which infect a number of botanical families.…”

Plant pathogenic bacteria in open irrigation systems: what risk for crop health?

“…Understanding how PPB can evolve in water in different seasons might represent a fundamental step in understanding disease emergences. In fact, water represents not only a simple reservoir for PPB and bacteria in general, but also a habitat with specific abiotic and biotic stress factors that might drive evolution of pathogenicity determinants in bacteria (Bartoli et al, 2015).…”

Bacterial Diseases of Crops

“…Soil contamination by herbicides, pesticides, heavy metals, and other toxic aromatic compounds provoke direct damage to plants by causing stress once they are assimilated and on the other hand they can influence the beneficial microflora associated with plants thereby altering their balance (Glassman and Casper, 2012;Siddiqui and Ahmed, 2006). Plant pathogens such as P. syringae seem to have acquired the capacity to metabolize aromatic compounds (Bartoli et al, 2015), which might be the result of long-time heavy use of herbicides (e.g., glyphosate or atrazine). The capacity of these pathogens to metabolize aromatic compounds represents a serious threat to the durability of agriculture since such compounds (e.g., phenolic substances) are generally produced by plants for their defense followed by pathogen attacks.…”