Wheat rust evolution in Spain: an historical review

Rusts are important wheat diseases worldwide. The three rust diseases of wheat are yellow rust, leaf rust and stem rust, and each has characteristic features. The Guadalquivir valley in the south–west and Girona in the north–east are the areas Spain most affected by these diseases. Key factors for understanding the history of wheat rust epidemics in Spain are historical weather records in the rust–prone areas and characterization of rust resistance in historical varieties currently preserved in seed banks. These diseases in Spain have been of moderate importance, with stem rust being the most significant disease. During the second half of the 20th century several major epidemics occurred. In 1958 and 1978 severe outbreaks of yellow rust occurred in the Guadalquivir valley. These were probably associated with crop intensification, especially a large number of host landraces replaced by just a few cultivars, as well as immigration of external pathogen inoculum. From the early 1970s, CIMMYT elite cultivars arrived in Spain. These possessed good resistance to leaf and stem rust (Sr2), and had early heading dates. Subsequently, stem rust severity rapidly decreased in Spanish fields, but leaf rust epidemics became frequent during 1998–2008 on durum wheat in south–west Spain. In 2013, races virulent on Lr14a gene were first reported in Spain, but they did not result in disease epidemics. In 2012–16 yellow rust epidemics were recorded at many locations due to incursion of the ‘Warrior’ race. Despite the availability of effective fungicides and resistant cultivars to manage the three rust diseases, these diseases continue to threaten wheat production in Spain. In 2016, stem rust caused epidemics on durum wheat in Sicily (Italy), which has similar climatic conditions to those found in the south and east of Spain. Alert systems and international co-operation are needed to characterize the resistance of cultivars, and to monitor the movement and virulence of the wheat rust fungi.