Phaeosphaeria nodorum leaf blotch

Environmental change could alter disease transmission routes

3 February 2010 

Many human, animal and crop pathogens transmit to new hosts by infection and by transfer to the infected host’s offspring. Researchers at Rothamsted Research, an Institute of the BBSRC, and colleagues from the University of Reading have demonstrated that this can lead to the simultaneous existence of two evolutionary stable states and the balance between these two modes of infection can change in response to environmental cues or disease control programmes. Their report appears in Proceedings of the Royal Society B today.

The wheat fungal pathogen, Phaeosphaeria nodorum, causes leaf blotch and is transmitted by spores splashed on leaves or by transfer to the seeds of infected plants. The pathogen has to make specific adaptations to switch the balance between transmission routes; producing more spores to achieve direct infection of the leaves, or reducing spore production to infect the seeds. In this new study researchers used mathematical models coupled with experimental data to show that this pathogen, jumped twice between these two infection states over a 160 year period.

Using their mathematical models the researchers investigated the effects of switching between these two transmission routes and how that impacted upon disease spread in wheat. This revealed that the existence of two stable forms can lead to a sudden change in the balance between transmission routes.

To test the model, the researchers tested seed and leaf samples collected over 160 years. The Broadbalk experiment at Rothamsted Research, on the cultivation of wheat, has been continuously run since 1843. Since then scientists have collected samples of soil, leaves and seeds. By comparing the amount of fungal DNA on seeds and leaf samples up until 2003, researchers were able to observe a shift in transmission route, with a jump to infected seed transmission in the early twentieth century a jump back to infection of the leaves around 1960.

Dr van den Bosch said "This finding has implications for human, animal and plant diseases. An ill judged change in a disease control programme can cause the pathogen to evolve a new, possibly more damaging, combination of transmission modes. Similarly, environmental cues, such as climate change, can shift the balance between transmission modes with adverse effects on human, animal and plant health."

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Rothamsted Research is an institute of the Biotechnology and Biological Sciences Research Council