Keeping track of rust

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‘The disease that never sleeps’ is how Nobel Prize winner Norman Borlaug once described wheat rust, a group of deadly, constantly changing fungal pathogens that pose a serious threat to food security worldwide.

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Globally, the three wheat rusts – stem, leaf and stripe rust – are the most economically damaging diseases of wheat. All inflict devastating losses when epidemics occur, but stem and stripe rust are the most feared, inflicting losses of 60% or more under favorable conditions. Successful control of stem rust – mainly through resistance breeding – is estimated to have saved farmers worldwide over US$1 billion annually for more than four decades. However, past wheat breeding successes cannot protect the world’s wheat crop indefinitely against this constantly changing enemy. With new rust threats emerging, scientists have implemented a global rust tracking system to try to stay ahead of their evolving enemy.

The Global Cereal Rust Monitoring System was initiated in 2008 as part of the Durable Rust Resistance in Wheat (DRRW) project, generously funded by the Bill & Melinda Gates Foundation and the UK Department for International Development. The rust tracking system now covers 38 countries and includes most of the wheat grown in developing countries. Information from field surveys, pathotype analysis and predictive models are stored in a state-of-the-art data management system (the Wheat Rust Toolbox) and made available via theRustTracker information system developed by CIMMYT in collaboration with partners from the Global Rust Reference Centre, Denmark’s Aarhus UniversityICARDA, and others.

“The aim of RustTracker is to provide a single source of information relating to global rust monitoring activities,” says CIMMYT’s Dave Hodson who coordinates the rust monitoring work. “Regularly updated information can provide rapid notifications of important pathogen changes or movements, new outbreaks, or risks of outbreaks. No other comparable monitoring system for a major crop disease currently exists at such a wide geographical scale.”

WHEAT photoUg99, an especially virulent strain of stem rust first identified in Uganda in 1999, was the catalyst for developing the rust tracking system. Eight closely related variants of Ug99 now exist and have spread to 11 countries between South Africa and Sudan and across the Red Sea to Yemen and Iran. With a large proportion of the world’s wheat estimated to be susceptible to the Ug99 races, the threat to South Asia is a major concern. The region, home to 1.4 billion people, produces around 20% of the world’s wheat; small-scale farmers without access to fungicides are particularly vulnerable.

In recent years, new, highly aggressive strains of stripe rust (also known as yellow rust) affecting many of the most widely grown wheat varieties have emerged and caused devastating epidemics in Azerbaijan, Ethiopia, Iraq, Morocco, Syria, Tajikistan, and Uzbekistan, with national yield losses as high as 40%. Using information in RustTracker – for example ‘risk maps’ based on country survey data – the aim is to help researchers in countries in the path of virulent rust strains to assess the severity of the threat and prepare. Pakistan is a typical example: here national rust surveillance efforts are coordinated by Atiq ur Rehman Rattu (NARC, Islamabad), extensive surveys are undertaken annually throughout the major wheat growing areas and all the information is uploaded into the RustTracker system.

Within five years, the rust tracking system has developed into one of the most extensive and fully functional global crop disease monitoring platforms. Through a global network of partners it has successfully tracked the spread and evolution of important new races, such as the Ug99 race group. The system is continually updated by in-country partners uploading field survey data and providing samples for analysis. Mobile technologies, such as smartphones and tablets, are now being used to collect survey data and transfer it from the field into the core databases. New molecular diagnostic tools developed by the USDA-ARS Cereals Disease Laboratory, Minnesota, are providing rapid detection of Ug99 races in samples collected from farmers’ fields. However, all of the rust surveillance activities only have relevance if they inform the wheat variety improvement efforts. Hence strong linkages to core wheat cultivar databases such as the CIMMYT Wheat Atlas and Genetic Resources Information System for Wheat and Triticale (GRIS) are being developed to ensure that both host and pathogen information are connected.

The next steps for rust surveillance include a geographical expansion of coverage (targeting 40 countries contributing annually), increased capacity for collaborating partners through enhanced training, and improved coverage of a wider range of rust diseases, especially stripe rust. Through a new collaboration with Cambridge University, UK, Hodson is hopeful that the initiative can make further progress on disease early warning and mitigation advice. The other major challenge is to ensure the long-term sustainability of the global rust monitoring system. This is critical given the continual emergence of new, virulent rust races. A failure of the global monitoring system and the allied control and mitigation efforts would undoubtedly result in re-emerging threats to wheat production and food security.