Rust diseases, caused by Puccinia spp., are among the most important causes of yield loss of cereal crops in the US and worldwide. Global surveillance of cereal rusts with the goal of identifying and monitoring new and highly virulent races as they emerge, is an important mitigation strategy to ensure the timely deployment of control measures in vulnerable cereal production areas. The US Department of Agriculture-Agricultural Research Service Foreign Disease-Weed Science Research Unit (FDWSRU) plays a critical role in global surveillance efforts, receiving and increasing exotic samples of cereal rusts collected by cooperators at institutes in East and North Africa, Europe, and South and Central Asia under USDA APHIS PPQ permit. Rust samples are processed in the BL-3 Plant Pathogen Containment facility at FDWSRU, including recovery, increase, and archiving of live rust cultures. A preliminary race analysis is also performed by testing on selected differential lines. Increased rust cultures are shipped to the USDA-ARS Cereal Disease Laboratory in St Paul (MN) for further analyses. To date, we have processed 1372 wheat rust samples from 23 foreign countries. Analyses derived from these rust cultures have enabled us to monitor the spread of highly virulent races, such Ug-99, and to identify hot spots around the world where diverse virulence combinations are generated and sustained through sexual cycles of the pathogen. Curated isolates also serve as valuable genetic stocks for studies in population genetics and for identifying new sources of resistance.
