Plant Pathogen Dispersal

Abstract

Plant disease epidemics require plant pathogens to be dispersed to infect new hosts. Understanding dispersal is important for devising methods to improve detection and control of plant pathogens. This is not straightforward, as plant pathogens can be dispersed by air, rain, water or soil, and by vectors such as animals, pollen, various microbes, people and machinery and on infected plant material including seeds. Epidemics vary in time and space as a result of complex processes affecting inoculum availability and production, dispersal and survival processes, and also the coincidence of susceptible crop plants, which each interact with the weather. To reduce disease, exposure of crops to inoculum is often limited by separating crops in time and space, using crop rotation, including different varieties. A wide range of diagnostic methods are increasingly used to help with this by detecting plant pathogens before infection occurs to prevent introduction of exotic inoculum, or to improve applications of crop protection products.

Key Concepts:

  • Plant pathogens include fungi, protists (such as oomycetes and plasmodiophorids), bacteria, phytoplasmas, viruses and viroids. For plant disease epidemics to occur, these plant pathogens must be dispersed to infect new hosts.

  • Plant pathogens can be dispersed by air, rain, water, soil, by animals, people and machinery and through infected plant material including pollen and seeds.

  • A key method for crop protection is to limit dispersal by separating susceptible crops in time and space by crop rotation, use of different varieties, hygiene or management of inoculum and use of crop protection products (biologicals and pesticides) at key growth stages or when infection conditions are suitable.

  • Some pathogens that are dispersed by air are adapted to survive freezing temperatures, high UV light levels and desiccation, whereas others only remain viable for short periods or in certain less extreme conditions. Some may even induce ice nucleation to promote rainfall to return them to the ground.

  • Some plant pathogens are dispersed in rain‐splash, usually short distances but occasionally longer when combined with strong winds. Pathogens can be dispersed in water films and groundwater or rivers.

  • Insects and other invertebrates, pollen and protists may vector some pathogens, mainly viruses, viroids and phytoplasmas.

  • One of the main reasons for new introductions of plant pathogens to a territory is introduction by people, as infected plant material, infected seeds or as contamination on clothing, machinery, food or other imported materials. Various statutory quarantine regulations and inspections by plant health professionals aim to reduce introductions.

  • Climate change may help pathogens to establish in new territories where they were previously absent.

Keywords: epidemics; plant disease; plant pathogens; inoculum; aerobiology; rain‐splash; soilborne; diagnostics; quarantine

Figure 1.

A summary of plant pathogen dispersal processes: soilborne pathogens that are also wind‐blown or vectored, rain‐splash and water, airborne (various spores, cells and biological debris), and vectors (insects (aphids illustrated), fungi (ergots on wheat, which are transported in seed and produce insect‐vectored conidia in ‘honeydew’), pollen (grass and pine pollen shown, which can contain viruses), and people, who are responsible for introductions in imported plants, food and other materials). The centre‐left photo of rain is provided courtesy of Prof. John Lacey (Rothamsted Research).

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Further Reading

Agrios GN (2005) Plant Pathology, 5th edn., p. 952. Amsterdam: Elsevier.

Web Links

http://ready.arl.noaa.gov/HYSPLIT.php

http://www.ars.usda.gov/Main/docs.htm?docid=14549

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West, Jonathan S(Feb 2014) Plant Pathogen Dispersal. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0021272]