WHEAT DISEASES
Stem rust
Figure 1. Pustules parallel to long axis of leaf/stem.
Figure 2. Severe infection.
CAUSAL ORGANISM
Fungus: Puccinia graminis
COMMON NAMES
Stem rust of cereals; wheat rust; wheat stem rust; stem
rust; black stem rust; black rust
HOST RANGE
Primary hosts:
Avena sativa (oats), Dactylis glomerata (orchardgrass),
Festuca arundinacea (reed fescue), Hordeum vulgare
(barley), Lolium perenne (perennial ryegrass), Poa
pratensis (meadowgrass), Secale cereale (rye), Triticum
aestivum (wheat), Triticum turgidum (durum wheat) , X
Triticosecale (triticale).
Different forms of the stem rust fungus infect the above
hosts, e.g. P. graminis f. sp. tritici infects wheat, P.
graminis f. sp. avenae infects oat, and P graminis f. sp.
secalis infects rye. Some of these pathogens have wider
host ranges than the primary host.
Wild hosts:
Elymus repens (quackgrass), Hordeum murinum (wild
barley), Lolium multiflorum (Italian ryegrass), Bromus spp..
SYMPTOMS
Symptoms are produced on almost all aerial parts of the
wheat plant but are most common on stems, leaf sheathes
and upper and lower leaf surfaces. The disease is first
seen as elongated elliptical blisters on the leaves and
stems of the plant running parallel to the long axis of the
leaf or stem (Fig. 1). Rust pustules (uredinia) are reddishbrown erupting through the epidermis to release masses of
powdery rust-coloured spores; tattered epidermal tissue
surrounds the uredinia. The pustules are dusty in
appearance due to the vast number of spores produced
and feel rough when gently feeling the plant tissue between
the thumb and forefinger. The pustules coalesce to cover
large areas of the host tissue in heavy infection (Fig. 2).
Under these conditions stems become weakened and
lodge. Later in the season, the colour of the pustules
changes from rust coloured to black as teliospores (resting
spores) are produced.
IMPORTANCE
Stem rust is present in South Africa and of particularl importance on spring wheat planted in the Western Cape.
Widespread epidemics are infrequent, but disease within a region or in individual fields can frequently be severe, resulting in
the destruction of between 50 and 70% of the crop. Yield loss due to fungal damage is greatest when the disease becomes
severe before the grain is completely formed. Infection damages the conducting tissue which decreases the amount of
nutrients transported to the grain, causing it to shrivel. Stem rust is probably the most destructive rust disease on wheat as it
also causes severe straw breakage and lodging.
Like other cereal rusts, P. graminis is capable of forming new virulent physiologic races in a very short time to overcome
resistance in existing wheat cultivars. This is referred to as the “boom-and-bust cycle”. Surveys are now performed annually
in many countries, including South Africa, to identify different and/or new races using a differential set of wheat cultivars.
The occurrence and step-wise migration of the stem rust race Ug99 is an example of a new virulent race posing a serious
threat to wheat production in many parts of the world.
Stem Rust Fact Sheet, Version 1. Copyright © 2010 PANNAR Seed (Pty) Ltd . Updated versions available from www.pannar.co.za.
Compiled by Rikus Kloppers and Stephanie Tweer. Comments/feedback can be sent to [email protected].
Disclaimer: This document serves as a guideline and is given in good faith.
WHEAT DISEASES
Stem rust
Figure 3. (a) Stripe rust, (b) stem rust and (c) leaf rust.
Figure 4. Rain/dew conditions conducive to disease development.
SIMILARITY TO OTHER DISEASES
P. graminis can be differentiated from other rusts of wheat by pustule size (uredinia of stem rust are larger than those of
stripe and leaf rust), shape, colour (red-brown colour), the presence of torn epidermal tissue surrounding pustules, and the
random arrangement of the uredinia over both leaf surfaces) (Fig. 3) (refer to Stripe Rust and Leaf Rust fact sheets).
DISEASE INFORMATION
Warm, humid climates favour severe epidemics. Stem rust can develop over a wide range of temperatures (18-29°C) but
optimally near 24°C and development slows at temperatures below 15°C. Spores germinate when they come into contact
with free water (dew or rain) (Fig. 4). Periods of low light intensity are also required for germination and penetration. The
time between infection and symptom expression varies from 10 to 15 days.
The spores survive within infected wheat fields on volunteer cereal plants or on successive crops, as they are planted at
different times of the year depending mainly on altitude and rainfall patterns. Infected volunteer plants along roadsides often
contribute to the survival of rust spores. Spores are spread by plant-to-plant contact and by air dispersal. In addition, spores
may be transported by wind over long distances, thus the occurrence of stem rust is only limited by the deposition pattern of
the spores, suitable weather conditions and the availability of susceptible hosts. The moderate climates and the ability to
grow cereals at any time of the year creates local endemic disease cycles. The disease is most severe when a susceptible
host is present and crop maturity is delayed.
CONTROL
Cultural control:
Use of resistant cultivars is the primary means of controlling stem rust. Early maturing cultivars also tend to escape
heavy losses as a result of stem rust infection. All PANNAR wheat varieties are annually screened for resistance
against the prevalent races and the information on PANNAR varieties is available on request.
Chemical control:
The use of these chemicals is generally less effective as with the other rusts as a proper penetration of the chemical into
the wheat canopy is required, and could be costly. In addition, successful chemical control of stem rust depends on
applying the fungicide before the disease reaches epidemic status.
Stem Rust Fact Sheet, Version 1. Copyright © 2010 PANNAR Seed (Pty) Ltd . Updated versions available from www.pannar.co.za.
Compiled by Rikus Kloppers and Stephanie Tweer. Comments/feedback can be sent to [email protected].
Disclaimer: This document serves as a guideline and is given in good faith.