Shifting boundaries: challenges for rust monitoring

Major changes have occurred in the global wheat-rust disease landscape over the last century. At the turn of the twentieth century pioneering rust research was driven by the need to combat devastating stem rust epidemics. A fundamental understanding of rust genetics and dispersal pathways emerged from this early work. Stem rust epidemics were also the driver behind the breeding programs that resulted in the green revolution of the 1960/70s. Successful incorporation of durable stem rust resistance into high yielding semi-dwarf wheat cultivars would change the wheat-rust disease situation beyond recognition. Associated intensification of the wheat cropping systems would also produce dramatic changes. Despite localized outbreaks, by the early 1990s stem rust was a disease under control. During this period of low stem rust incidence, yellow rust began to emerge as a substantial threat. Breakdown of Yr9 resistance resulted in damaging epidemics in Asia; an exotic incursion introduced yellow rust into Australia with highly significant subsequent impacts. The Australian incursion was almost certainly transmitted via an air traveller and the exponential growth in international air travel has increased the probability of other cross-continental movements. By the start of the twenty-first century, new rust threats had emerged. Durable stem rust resistance was broken down by the Ug99 race lineage identified in East Africa; new aggressive strains of yellow rust adapted to warmer temperatures were identified and spread across continents at a rapid rate. As in the past, major rust developments are one driver of global initiatives to mitigate the threat. Climate change and the response of pathogens to changing conditions are possible emerging issues, although other changes may prove to be more significant. Throughout this century of change a consistent theme is the adaptability of wheat-rust pathogens to cause recurring damage. Maintaining the gains of the previous decades will require sustained, collaborative, multi-disciplinary efforts. To keep pace with the evolving threats posed by wheat rusts there is a clear need for continuous vigilance and surveillance of both pathogen and host. Current international monitoring and surveillance efforts are described along with associated challenges.