Studies of cereal pathogen populations in the UK have shown rusts are becoming increasingly diverse – affecting varieties in different, and often unpredictable, ways – and crops should be monitored closely.
This was a key message arising from today’s UK Cereals Pathogen Virulence Survey (UKCPVS) stakeholder event in Cambridgeshire. Managed by NIAB, and funded by HGCA and Fera, UKCPVS receives infected cereal leaf samples from agronomists, trials officers and researchers. From these samples, pathogen isolates are selected and tested to check their virulence against wheat and barley varieties. The testing can detect new races of cereal pathogens capable of causing disease on previously resistant cereal varieties. Targeted at breeders, crop scientists and technical agronomists, the event reported on recent seedling test results (using samples received during 2014) and adult plant nursery tests (using samples received during 2013).
1. Yellow rust: latest results from UKCPVS
The samples received by UKCPVS in 2014 were dominated by Warrior-type isolates (25 of the 27 tested to date). This mirrors the trend of the past few years. By testing pathogen virulence on varieties with known resistance genes, four distinct groups within the Warrior-type race have been characterised (Warrior 1-4) and the rise and fall of each group within the UK population has been monitored.
Dr Sarah Holdgate, UKCPVS project manager based at NIAB, said: “When it was originally detected in 2011, Warrior 1 was dominant but since then it has declined, with Warrior 3 increasing in frequency. In addition to the number of Warrior groups currently identified in the UK, our work also shows the groups themselves carry a diverse range of virulence genes – meaning they can infect wheat crops to varying degrees.
“In fact, some of the latest isolates have presented the UKCPVS with a challenge in how to name the races – there are now Warrior races which fail to cause disease on the variety Warrior. We are looking at a new naming approach and isolates which we call Warrior 1 could have a new name later in the year.”
Both Warrior-type and Solstice-type isolates from 2013 were used in adult plant tests. Encouragingly, 20 out of 41 of the current Recommended List varieties were resistant to all isolates tested.
2. Yellow rust: further information
The latest information on seedling and adult plant resistance against yellow rust for current Recommended List winter wheat varieties was published by HGCA in February.
Dr Jenna Watts, HGCA Research Manager, said: “The disease ratings presented in the HGCA Recommended List provide information on the adult plant resistance of varieties, as this is the most important stage for growers. However, it is important to note that a variety can be susceptible at the seedling stage, before stem extension, but resistant at the adult plant stage. This explains why yellow rust is sometimes seen in the autumn and winter on varieties with high Recommended List disease ratings.
“Last autumn was a prime example – the combination of a large spore load from the summer coupled with the mild autumn conditions resulted in early yellow rust symptoms, even on some varieties with a high adult plant disease rating. Adult plant resistance means affected plants should outgrow the disease at a later growth stage. The information provided by UKCPVS on the seedling resistance of varieties provides really useful information when used alongside the adult plant resistance information presented through the HGCA Recommended List.”
3. Yellow rust: demise of diversification grouping
UKCPVS data can be used to group varieties according to their reaction to different rust isolates collected in the previous year.For almost 40 years, the UKCPVS has produced diversification tables, to encourage growing of varieties with a diverse mixture of resistance genes. Due to the diversity of the current Warrior race, diversification grouping has not been possible this year.
“As part of an integrated disease management programme, where susceptible varieties are selected, they should be grown alongside more resistant varieties to limit the spread of the disease,” said Dr Holdgate.
4. Brown rust: latest results from UKCPVS
Dr Holdgate continued: “Our tests show the wheat brown rust population has changed over the past two years and seedling tests reveal isolates are becoming more complex. In 2006, most isolates tested carried two virulence genes. In 2014, most isolates tested carried six. The frequency of virulence genes present in the brown population has changed too – some virulence genes have increased markedly, whereas others have declined. The dominant six-gene isolate appears similar to isolates from the Glasgow race, first identified in 2006. As this race has been seen before, this shift would be classed as a re-emergence, rather than a new race.”
Both wheat and barley powdery mildew were surveyed in 2014. Based on seedling tests, virulence frequencies were broadly similar to previous years.
6. Thoughts on the 2015 season
Both yellow rust and brown rust have been active in crops during the autumn and winter, creating the potential for a significant epidemic development this spring. Close monitoring of high-risk crops, applying a suitable protectant product and maintaining protection throughout the season will be important to help realise yields.
The latest disease management information can be found at www.hgca.com/disease
7. UKCPVS needs you
The success of the UKCPVS depends on samples received from the industry. If you would like to get involved in the survey, full sampling instructions are available from Amelia Hubbard (Amelia.email@example.com) or via www.hgca.com/ukcpvs