BSPP News Summer 2001 - Online Edition

The Newsletter of the British Society for Plant Pathology
Number 39, Summer 2001 

Durable Disease Resistance Symposium - Key to Sustainable Agriculture
Wageningen, the Netherlands : 28 November -  December 2000

This symposium, held in Ede-Wageningen, had an international flavour and was attended by over 200 delegates from all over the world.  The opening lecture was delivered by Professor Evert Jacobsen from the Plant Sciences Department at Wageningen University.  He focussed on breeding and remarked on the considerable contribution made to durable disease resistance research by Jan Parlevliet.  At this point the well-known Dutch figure, Sinter Klaas, made his entrance to present Jan with an impressive plaque displaying the conference logo.  After a few traditional Dutch songs in keeping with the season it was back down to business with a plenary session on "Durability of resistance - the present situation". This neatly set the scene with presentations covering resistance against fungi, bacteria, viruses, and nematodes.  It somehow seemed very appropriate that the first speaker was Jan Parlevliet who explained why no resistance was truly durable in an evolutionary sense.

Bruce McDonald from the Institute of Plant Sciences, Swiss Federal Institute of Technology, Zurich, gave an excellent presentation on "Pathogen population genetics and the durability of disease resistance".  Bruce stated that resistance durability is affected by the evolutionary potential of the pathogen population and therefore it is important to understand the genetic structure of that population.  Pathogens with both sexual and asexual reproduction phases during the growing season have a high potential for gene flow and so pose a higher risk of breaking down resistance.  In contrast, pathogens with strict asexual production present a lower risk since there was a lower potential for gene flow. A model based on this premise was proposed to assist with breeding strategies for durable disease resistance.

In the evening session Dr Corne Pieterse from the Faculty of Biology at Utrecht University gave an excellent presentation on "Enhancement of induced resistance by simultaneous activation of salicylate and jasmonate dependent defense pathways in Arabidopsis thaliana".  Corne presented evidence that simultaneous activation of systemic acquired resistance (SAR) and induced systemic resistance (ISR) in Arabidopsis can provide a greater level of resistance to Ps. syringea pv. tomato than SAR or ISR provides alone. The additive effect appears to be a result of the induction of complementary NPR1-dependent resistance mechanisms rather than simply due to a higher level of SAR induced mechanisms (i.e. PR-1-transcript accumulation was similar in plants expressing SAR/ISR as in those expressing only SAR).  However, the mechanism underlying the divergence of SAR and ISR beyond NPR1 is not known.   It was proposed that combining SAR and ISR may offer a more effective and durable biocontrol option for the suppression of plant disease.

Barbara Pennypacker from Pennsylvania State University gave the last presentation on the first day and discussed whether sensitivity to light, and thus carbon flux, impacts on the expression of qualitative and quantitative resistance.  In full light Alfalfa has quantitative resistance to Verticillium wilt and qualitative resistance to Fusarium wilt.  However, under low light conditions expression of quantitative resistance fails whilst qualitative resistance is unaffected.  It was proposed that quantitative resistance requires a greater carbon flux through secondary metabolite production for its expression than qualitative resistance.  If this is the case then environmental factors that reduce carbon flow may suppress expression of quantitative resistance.

One of the highlights of the conference was undoubtedly the talk presented by Professor Jean-Pierre Metraux  from the University of Fribourg, Switzerland.  He focussed primarily on the SAR signal transduction and discussed the impact of light perception on SAR expression as an example of crosstalk that occurs between different cell signalling pathways.  Jean-Pierre showed that light perception is important for SAR expression, for example, the induction of PR-1 by salicylic acid or benzothiadiazole is strongly dependent on light.  A Boolean network model was presented as a framework to study interactions between the various signal transduction pathways for induced resistance and light perception.  It was proposed that this model provides a representation of the signalling network, which can aid experimental design.

Perhaps one of the most thought provoking presentations was made by Deon Struthman, University of Minnesota, who described host plant resistance as a natural resource.  He reminded us that, as stewards of these natural resources, we have responsibility to use them wisely and avoid excessive consumption.  Failure to do so may have regrettable consequences including defeated genes and disease epidemics with the inevitable associated financial and social costs.

Overall the conference program was quite intensive but was run very smoothly by the organisers who ensured that all speakers kept to time.  The standard of oral and poster presentations was generally very good.  I would like to thank the British Society for Plant Pathology and HortResearch for providing financial support to attend the conference and also to thank the conference organisers for giving me the opportunity to make a presentation.

Tony Reglinski
HortResearch, New Zealand