Stem (black) rust life cycle and risk to UK wheat

In the UK, severe outbreaks of stem rust are extremely rare. The pathogen has a complex life cycle, which depends on the presence of hosts (wheat and barberry) and favourable conditions – especially high temperature and suitable air movement.

• Environmental conditions have become more conducive to support stem rust infection over past 25 years
• In 2013, stem rust was recorded in UK crops for the first time in over 60 years
• Since then, the disease has been observed in several years at several sites
• It is important to monitor the occurrence of stem rust in the UK

• The fungus that causes stem rust (Puccinia graminis f .sp. tritici) has several spore stages
• It requires wheat and barberry hosts to complete its life cycle
• The pathogen also requires high temperatures (the optimum temperature is above 20°C)
• As temperatures below 15°C inhibit development of the disease, it rarely occurs in the UK and associated yield losses tend to be small

Urediniospores

In Britain, airborne urediniospores generally originate from South West Europe and North Africa. These spores, when air movements are appropriate, cause initial infection on wheat.

Teliospores

Relatively late in the season, black elongated pustules containing the teliospores develop, mainly on the stems. These spores overwinter on wheat stubble.

Basidiospores

Eventually, teliospores produce secondary spores – basidiospores – which infect barberry (Berberis spp.), where the pathogen enters a sexual phase.

Aeciospores

On barberry, aeciospores are produced which can infect crops in close proximity (e.g. wheat close to field edges) very late in the season.

Uredospores

In wheat, infection by aeciospores gives rise to the uredospore stage. This stage is associated with typical symptoms on wheat – orange/brown sporulating pustules, which occur in stripes on leaves and stems.

Stem rust symptoms on wheat (left) and barberry (right) leaves.

Classic stem rust infection symptoms – on stems, leaves, and ears – were detected in untreated winter wheat plots at a Recommended Lists (RL) trial site in Lincolnshire during 2022.

Above: Stem symptoms

Above: Leaf symptoms

• Based on recent screens, it is likely that many UK wheat varieties are highly susceptible to stem rust.
• However, good control levels can be achieved with rust-active azole fungicides, especially tebuconazole.

If you suspect that stem rust is present in your crops, you can send in a tissue sample for analysis (stems or leaves). This will aid the UK monitoring of this disease.

The process is the same as the UKCPVS process for yellow rust and brown rust, except the mailing address.

Send stem rust samples to:

Diane Saunders

John Innes Centre

Norwich Research Park

Norwich

NR4 7UH

Tel: 01603 450000

Do not send samples to UKCPVS.

Presentations by Diane Saunders, John Innes Centre.