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The 3rd International Workshop on Barley Leaf Blights was held in the University of Alberta Conference Centre, Edmonton, Canada in July 2006. More than 80 scientists from 18 countries attended the workshop, which covered a wide range of topics including pathogen population biology, disease epidemiology, genetics of resistance, breeding and disease management. During the workshop, participants also discussed the focus for future research and agreed that more should be done on Ramularia, an emerging barley disease in Europe as well as other parts of world. On the last day, a tour was organized to Agriculture and Agri-Food Canada and Alberta Agriculture, Food and Rural Development at Lacombe, providing an opportunity to view the facilities and research programs in the two organizations.
Scald caused by Rhynchosporium secalis was one focus of the workshop. About 50% of presentations were dedicated to this disease. Consistent with published results, high genetic variation in R. secalis was reported. Using neutral molecular markers, Pascal Zaffarano (Switzerland) proposed that the centre of origin for R. secalis is in Scandinavia as pathogen populations sampled from this region display higher genetic variation than those from the Fertile Crescent, the agreed centre of origin for barley. It was commented by some participants that higher genetic variation found in the Scandinavian region might be due to other factors such as effective population size. Sexual reproduction in R. secalis was also intensively discussed. Although many population and epidemic studies suggest a sexual cycle, and the majority of participants agreed with this, no teleomorph has been identified. It was hypothesized that the sexual cycle may occur only on stubble, volunteer hosts or other secondary hosts such as grasses or even oak trees, making it hard to observe. Using a combination of molecular markers, mark-release-recapture technology and Bayesian approach, Mathew Abang (ICARDA) presented some evidence of a sexual cycle during the barley growing seasons in Syria but this result needs to be verified.
Fungicides and resistant cultivars are still the major approaches to control barley scald. It seems that in many places, the time and frequency of applying fungicides depends mainly on affordability and preference, rather than necessity and efficiency. Three speakers were invited to give their opinions about fungicide application from the perspectives of manufacturers, farmers and extension scientists. Kequan Xi (Alberta Agriculture, Food and Rural Development, Canada) pointed out that cultivars with major-gene-mediated resistance may lose their effectiveness within 2-3 year s of consecutive cultivation. This led to a lengthy discussion on resistance gene conservation and sustainable disease management, which was chaired by Amor Yahyaoui (ICARDA). My view was that because R. secalis is a highly variable pathogen and the majority of genetic variation is distributed within local areas, this pathogen can adapt rapidly to control measures. Traditional methods of using major resistance genes and fungicides with simple modes of action are not likely to be durable for controlling R. secalis. The critical issue for sustainable disease management is to curb the emergence of new virulences and fungicide resistance in pathogen populations. Sustainable scald management could be achieved through an integrative disease program which is able to minimize the evolutionary potential of R. secalis by reducing its genetic variation, stabilize its evolutionary dynamics by diversifying selection pressure and prevent widespread distribution of pathotypes carrying new virulence and/or fungicide resistance by restricting its migration.
Diversification is a promising approach for controlling scald. Adrian Newton (SCRI) reported that mixing cultivars with different genetic backgrounds significantly increased yield and quality of barley due to the reduction of scald. He also pointed out that mixtures deployed in patches were better than homogenous mixtures. Rotation has been widely accepted as an environmentally friendly way to control plant disease. In many areas this approach is not practical due to climatic and other constrains, leading to continuous cultivation of the same crop. For example, in parts of Western Canada, barley has been continually grown on the same land for more than 20 years. However, resistance gene rotation could be used to control scald. Kelly Turkington (Agriculture and Agri-Food) reported that planting different cultivars on the same land substantially reduced scald severity compared to planting the same cultivars. Net blotch caused by Pyrenophora teres f. teres and P. teres f. maculate were another focus of the workshop, with work on genetic characterization of pathogens and host resistance. Leona Leisova (Czech Republic), Creg Platz (Australia) and others reported a high pathogenicity and neutral variation in the fungus and there were less spatial dynamics than temporal dynamics in pathogen populations. Both mating types were found in the Czech Republic but not in equal frequency. The development of several sets of differentials by Afanasenko Olga (All Russian Research Institute of Plant Protection) and Marja Jalli (MTT Agrifood Research, Finland) as well as AFLP mapping of avirulence genes by Tim Friesen (USDA, North Dakota) and QTL mapping of host resistance by Tajinder Grewal (Univ. Saskatchewan, Canada) will be useful to understand resistance in barley, screen breeding materials and study population genetics and evolution of the pathogens.
An emerging disease of barley, Ramularia was another part of the workshop. The disease has been discovered in many part of Europe and participants agreed that a European focus is required to better understand the genetics of Ramularia-barley interactions, the epidemiology of the disease, and strategies for control. Although not officially reported in North America, some “look like” Ramularia symptoms were found in the experimental fields of the Agriculture and Agri-Food Canada during our excursion.
The 4th International Workshop on Barley Leaf Blights is scheduled to be held in the Czech Republic in 2010.
Jiasui Zhan, SCRI, Scotland