BSPP News Spring 2000 - Online Edition

The Newsletter of the British Society for Plant Pathology
Number 36, Spring 2000 

Conference and Travel Reports

Fifth International Workshop on Septoria and Stagonospora Diseases of Cereals
CIMMYT, Mexico : 20 - 24 September 1999

Septoria tritici blotch and stagonospora nodorum blotch are two of the most important pathogens of wheat worldwide and are currently a major focus for resistance breeding and scientific research. This workshop was organised by Ravi Singh, Maarten van Ginkel and Linda Ainsworth from CIMMYT and the scientific program was arranged by the late Professor Zahir Eyal who was until recently one of the leading scientists in septoria research. Professor Eyal's many contributions to the field were frequently remembered throughout the workshop.

Dr Sanjaya Rajaram, the Director of the Wheat Program at CIMMYT, opened the workshop with a lecture introducing both the history and future challenges of the International Wheat Program. CIMMYT breeding strategies have been extremely successful over the years and CIMMYT germplasm has been used by wheat breeders throughout the world. This success is largely due to policies of targeted breeding for specific environments, use of diverse gene pools to maintain genetic diversity, shuttling of breeding lines between different environments and testing of material in multi-locational trials.

 
From left to right: Clare Ellerbrook, Penny Brading and Lia Arraiano
getting a close-up view of CIMMYT's maize breeding programme.

The first session on 'Pathogen Biology' started with an overview of the Septoria tritici (teleomorph Mycosphaerella graminicola) and Stagonospora nodorum (teleomorph Phaeosphaeria nodorum) pathogens given by Dr Al Scharen. This session also included presentations on DNA fingerprinting work with S. tritici, PCR-based assays developed to detect both S. tritici and S. nodorum on wheat leaves and a phylogenetic study of Septoria passerinii (causal agent of barley speckled leaf blotch) that revealed its close relationship with S. tritici. The next session moved on to compare and contrast the infection processes of these three pathogens.

'Host-parasite Interactions' were the topic of Session three and Dr Gert Kema described work on the genetics of avirulence in S. tritici. He has shown that avirulence of one particular isolate to several wheat varieties is controlled at a single locus. In my own presentation later in this session I described studies in wheat to investigate the genetics of specific resistance to this same isolate. These two complementary talks provided the first clear evidence that gene-for-gene relationships can exist between wheat and S. tritici isolates. Also in this session, Lia Arraiano described the use of various cytogenetic wheat stocks to investigate resistance to septoria tritici. These precise genetic stocks, held at the John Innes Centre, UK, provide a powerful tool for rapid location of resistance genes onto chromosomes. To end the session, Dr Lucy Gilchrist presented her analysis of the Septoria Monitoring Nursery at CIMMYT which has been established to evaluate the responses of germplasm to diverse pathogen populations under variable environmental conditions.


A colossal stone head of the Olmec culture, 1st Millenium BC, now outside the 
Museum of Anthropology, Mexico City.

Day two of the workshop began at 5 am when we boarded a bus to take us to CIMMYT's Toluca Research Station outside of Mexico City.

We spent a pleasant morning in the sunshine listening to field presentations about different aspects of the various cereal breeding programs run at Toluca. We were then treated to a fantastic Mexican style barbecue with no shortage of chillies!

Back to the grind the next day as we returned to 'Host-parasite Interactions', this time in stagonospora nodorum. Professor Edward Arsenuik described field trials comparing the virulence of  S. nodorum isolates on spring and winter triticale and wheat and concluded that screening with single isolates rather than mixtures is the most useful method to differentiate resistances. Dr Noel Murphy then gave two presentations about the inheritance of S. nodorum resistance conferred by a single gene from the wild wheat Triticum tauschii. Using bulked segregant analysis on an F2 mapping population he had also identified an RFLP marker linked to this resistance gene.


Lia Arraiano and Penny Brading at CIMMYT's wheat trial site at Toluca.

In the 'Population Dynamics' session Dr Bruce McDonald discussed genetic diversity and gene flow in field populations of S. tritici and S. nodorum collected from different parts of the world. RFLP comparisons indicate that sexual reproduction is more important than clonality for both fungi. Dr McDonald also argued that gene flow is sufficient to join large areas into single genetic populations. This session included a study of aggressiveness in Polish and US S. nodorum isolates (Dr Peter Ueng) and a talk by Christina Cowger describing the specific adaptation to virulence of S. tritici isolates on the resistant wheat variety 'Gene'.  Noel Murphy gave his third presentation, this time on the levels of genetic variability in a Western Australian S. nodorum isolate collection.

Session five covered the 'Epidemiology' of both pathogens with an excellent overview presented by Dr Mike Shaw. The modes of infection and spread both within and between crops were described and compared for both diseases.  S. nodorum grows and spreads faster than S. tritici under ideal conditions but is less tolerant to periods of dryness during the infection process indicating that weather assessment is vital for disease prediction. Dr Cristina Cordo then described studies of both weather variables and S. tritici disease severity in Argentina and Dr Gary Bergstrom reported on the epidemiology of seedborne S. nodorum in the New York area.

The session about 'Cultural Practices and Disease Management' of both septoria diseases was introduced by Dr Joseph Krupinsky. Factors influencing these diseases include crop rotation, stubble tillage, fertiliser addition and use of disease free seed (S. nodorum). Dr Chris Mundt continued this theme with a presentation about use of varietal mixtures and concluded that they reduce the severity of both diseases.

The final day of the workshop concentrated on 'Breeding for Disease Resistance' and Dr Maarten van Ginkel reviewed breeding strategies in general before describing those employed by CIMMYT. Other speakers in this session talked about the strategies, problems and progress made in individual breeding programs from different nations including USA, Uruguay, Mexico and Western Australia. Dr James Brown presented the results of collaborative field studies conducted in England, Holland and Switzerland which highlighted specific interactions between S. tritici isolates and wheat varieties.

The last session covered chemical control of the septoria diseases. Dr J. Verreet described the various fungicides used, their modes of action and how disease severity and crop yields are related to the timing of fungicide application. Lise Jorgensen, who is involved in a plant protection advisory panel providing decision support for farmers in Denmark, described tests which have resulted in the recommendation of new lower dose rates for strobilurin fungicides.

Overall this workshop provided a great opportunity for the majority of scientists and breeders working on the septoria diseases to meet and share their ideas and achievements and the opportunity to visit a centre as important in wheat breeding as CIMMYT was an added bonus. I am grateful to the BSPP for providing me with a travel grant to assist me in attending this valuable meeting. 
 
Penny Brading
John Innes Centre, Norwich