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An assessment was made of stem rust race analysis on a global scale. Responses were obtained from 23 rust workers representing 21 countries. Five laboratories have an institutional history in stem rust race analysis of more than 60 years, whereas personal experience in this field ranged from 0 to 35 years. The number of stem rust samples processed from 2006 to 2008 varied greatly between countries. For the three year period most collections were characterized in Canada, followed by Georgia, USA, South Africa and Australia. Most laboratories use the North American differential set and nomenclature system. However, these entries are often supplemented by additional tester lines from the Stakman set, other single gene lines or local cultivars. Differential sets varied between eight and 50 entries. More than half of the respondents indicated that they often encounter seed mixtures amongst their differentiating lines. In recent surveys most races were detected in Ethiopia, followed by Georgia and China. One race dominated the USA and Canadian stem rust population. In South America and Australia stem rust has been rare in commercial wheat for many years. Races within the Ug99 cluster were frequently identified in stem rust collections from Kenya and Ethiopia. Two races related to Ug99, but avirulent on Sr31, occur in South Africa. Several laboratories are in the process of purifying and bulking differential seed, which appears to be one of the major limiting factors in reliable stem rust race analysis. Improvement of infrastructure and training of individuals inexperienced with stem rust should improve global surveillance efforts. In addition, countries doing race analysis should keep viable culture collections in long-term storage.
Cereal rusts have long been the scourge of wheat farmers worldwide. Three fungal rusts are capable of inflicting serious economic damage to wheat; namely, leaf rust, stripe rust, and stem rust. Historically, stem rust was the most feared disease of wheat, but since the 1950s, effective resistance has protected crops and livelihoods. By the mid 1990s stem rust had been reduced to negligible levels worldwide. The detection of the Ug99 lineage of stem rust in Uganda in 1998 has challenged the assumption that stem rust was a conquered disease, and up to 80% of the world’s wheat is now considered stem rust susceptible. Ug99 has sparked a global effort by wheat scientists to counter the threat and has highlighted the need for effective surveillance and monitoring systems. Outside of a few developed countries, monitoring efforts are often irregular or even non-existent and no coordinated global surveillance effort currently exists. Ug99 has provided the impetus to implement a global surveillance and monitoring system that provides relevant and timely information as a global public good. Key components, current status and future plans for this emerging cereal rust monitoring system are described. The immediate concern regarding Ug99 makes it an initial priority focus, but the other cereal rusts cannot nor should be excluded. Lessons can be learned and parallels drawn from existing successful trans-boundary monitoring schemes such as the Desert Locust monitoring and early warning system implemented by the UN Food and Agriculture Organization (FAO). Successful networking, expanded capacity of partners, efficient field surveys and data handling, plus regular timely targeted information products are all components of the Desert Locust scheme that need to be transferred to a cereal rust monitoring system. Through a consortium of partners several advances have already been made targeting the Ug99 lineage of stem rust. GIS technology is forming the backbone of an emerging rust monitoring and surveillance system being developed collaboratively by international agricultural research centers, UN agencies and advanced research institutes. The system already incorporates a rapidly expanding volume of standardized geo-referenced field survey data, routine use of wind models and public domain web tools delivering information in near-real time. Several challenges still remain before a fully operational system is created, and these are outlined. The need for vigilance and a lack of complacency regarding unexpected events are highlighted. These might include; accidental assisted movements, natural long distance dispersal and the threat of rust pathogens occurring in “non-traditional” areas as a result of climate change.
Race (pathotype) surveys of cereal rust pathogens have been conducted in many parts of the world since the early 1900s. The only way to identify rust pathotypes remains virulence testing in greenhouse tests using genotypes (“differentials”) carrying different resistance genes. Virulence determinations have rarely targeted genes conferring adult plant resistance because of the technical difficulties of working with adult plants under controlled conditions. Where pathotype surveys have been conducted in a robust and relevant way, they have provided both information and pathogen isolates that underpinned rust control efforts, from gene discovery to post-release management of resistance resources. Information generated by pathotype surveys has been used to: devise breeding strategies; indicate the most relevant isolates for use in screening and breeding; define the distribution of virulence and virulence combinations; allow predictions of the effectiveness/ ineffectiveness of resistance genes; and issue advance warning to growers by identifying new pathotypes (both locally evolved and introduced) before they reach levels likely to cause significant economic damage. To be most effective, pathotype surveys should also provide fully characterized isolates (defined pathotypes) for use in identifying new sources of resistance and screening breeding material. Although constrained to some extent by a lack of markers, particularly those not subject to natural selection, surveys have also provided considerable insight into the dynamics of rust pathogen populations, including the evolution and maintenance of virulence, and migration pathways, including periodic long-distance migration events.