Keeping watch over yellow rust
The UK Cereal Pathogen Virulence Survey (UKCPVS) has monitored cereal rusts and mildews in the UK for more than 40 years. It aims to detect and warn the industry about new races of disease which threaten varietal resistance.
At the UKCPVS annual meeting, held on Thursday 6 March, speakers from NIAB outlined the main findings from the 2013 surveys. Guest speakers focused on yellow rust genetics with Dr Diane Saunders of the Sainsbury Laboratory explaining the situation in the UK and Dr Sajid Ali of the University of Agriculture in Peshawar giving the international picture.
In the UK yellow rust survey, “Warrior type” races were the most common; this type first appeared in 2011 and is virulent against a greater range of resistance genes than other races. Despite this, there are currently many winter wheat varieties with good resistance to yellow rust on the HGCA Recommended List 2014/15.
Dr Saunders’ research is looking again at samples collected in the survey over a number of years. Her team is investigating the genetic sequence of yellow rust to draw a genetic ‘family tree’ to see how the different races are related to each other. The results seem to show a lot of difference between “Warrior types” and other races of yellow rust in the UK, raising the possibility that the “Warrior type” may have been brought into the UK rather than evolving from a race already present.
The presentation given by Dr Ali supported this idea. As part of a multinational project he has mapped out diversity in yellow rust populations. The findings show that yellow rust in Northern Europe has less genetic diversity than other regions of the World, in particular the Himalayan region where the pathogen is able to reproduce sexually which can result in novel types emerging and an increase in population diversity. With increased global travel, there is a concern that new races could be spread more quickly than in the past where the wind was the main method of dispersal.
Plant breeders may need to consider the implications of Dr Saunders and Dr Ali’s results on the dispersal and diversity of yellow rust, to continue supplying UK farmers with rust-resistant wheat varieties.
Even with all this global research, there is still much to learn about yellow rust here in the UK and abroad, such as the effect of climate and the role of sexual reproduction. The UKCPVS is a crucial part of this effort and ensures that new knowledge of yellow rust is available to breeders and to growers through the HGCA Recommended List.
Amelia Hubbard and Dr Emma Coventry of NIAB also presented survey reports for brown rust and powdery mildew. The wheat brown rust population appears to be relatively stable although virulence for some resistance genes (Lr1 and Lr26) was more common compared to 2012 whereas virulence for Robigus (Lr28) declined slightly but was still present in 45% of the isolates tested in 2013.
For wheat powdery mildew, there have been no major changes since 2012. The pattern of virulence frequencies in barley powdery mildew has generally remained stable during 2013 compared to previous years
Both yellow rust and brown rust have been active in crops during the autumn and winter, creating the potential for epidemic development in the spring, depending on conditions. As new pathogen races can develop quickly it is important that all crops are monitored for disease and action taken to protect crops where appropriate. The HGCA information sheet 26 provides information on fungicide performance in wheat.
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