Stem rust, also known as cereal rust, black rust, red rust, or red dust, is a disease caused by the fungus Puccinia graminis f. sp. tritici in cereal crops, with susceptible Wheat being the most important host. Stem rust (black rust) is a common disease of barberry and other Berberis, Mahoberberis, and Mahonia species. It decreases grain quality and causes severe yield losses. The fungus affects the plant’s stem and leaves, causing rusty-colored pustules that burst and release spores of spores that spread the illness to neighboring plants.
Stem Rust disease management in Wheat
The causal organism of Stem rust disease
- Rust fungi are obligatory parasites that grow and reproduce on live host tissue.
- The species that causes stem rust, Puccinia graminis, is heteroecious, needing two unrelated host plants to complete its life cycle.
- Puccinia graminis is a macrocyclic organism with five spore phases.
- There is significant genetic variety within the species, with subspecies and races of the fungus known to exist.
- Puccinia graminis f. sp. tritici causes wheat stem rust, while P. graminis f.sp. secalis causes rye stem rust and P. graminis f.sp. avenae causes oat stem rust.
Disease cycle of Stem rust disease
It only survives on living hosts from one season to the next. The greatest carryover occurs during wet summers and autumns. Rust fragments can be spread quickly by wind, and the establishment of stem rust is favored by wet conditions and temperatures of 15-30°C. In comparison to stripe rust, stem rust typically appears later in the season.
Its obligate biotrophic lifestyle necessitates the activation of specific gene transcriptions. It constitutes biotrophy genomic features, which have parallels in other eukaryotic plant pathogens and show a convergent evolution around the plant pathogenic lifestyle.
The life cycle of Puccinia graminis
- Stage 0: Spermogonium stage. During this stage, the fungus produces spermatia and receptive hyphae.
- Stage I: Aecium stage. During this stage, the fungus produces aeciospores.
- Stage II: Uredium stage. During this stage, the fungus produces urediospores.
- Stage III: Telium stage. During this stage, the fungus produces teliospores.
- Stage IV: Basidium stage. During this stage, the fungus produces basidiospores.
Each of these spore stages plays a key role in the life cycle of Puccinia graminis; they contribute to the spread and survival of the fungus in the environment.
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Favorable conditions for the spread of Stem rust disease
- Both live on stubbles and volunteer crops, with a different host every time. Uredospores from the southern slopes cause Berberis spp. and principal spread.
- Disease growth is aided by moisture and temperatures over 20° C. text expansion.
- Optimal conditions for the development of stem rust include hot days (25-30°C) and mild nights (15-20°C) that allow dew to accumulate on the plant.
- Stem rust needs living plants to develop and propagate. To infect crops during the season, it must survive summer by infecting volunteer cereals or grass hosts, called the ‘green bridge.’
Symptoms of Stem Rust disease in Wheat
- Symptoms are formed on practically all aerial parts of the wheat plant. However, the stem, leaf sheaths, and upper and lower leaf surfaces are the most prevalent.
- Pustules (containing masses of urediospores) are dark reddish brown and can be seen on both sides of the leaves, stems, and spikes.
- Pustules are often discrete and dispersed, whereas serious infections -coalesce.
- “Fflecks” may occur before the development of pustules. The infection sites are harsh to the touch before the spore masses burst through the epidermis.
- The surface tissues become ripped and shredded when the spore masses burst through.
Causes of yield loss due to Stem Rust disease in Wheat crop
The stem rust fungus attacks the above-ground parts of wheat plants and reduces crop yield through several means:
- Absorbing nutrients
- Breaking the plant’s control of transpiration and causing desiccation
- Interfering with plant vascular tissue
- Weakening stems and causing lodging
- Potentially making mechanical harvesting impossible.
- It. can result in fewer tillers, fewer seeds, and in severe cases, plant death.
Stem rust disease management in Wheat by Cultural methods
- Crop rotation with mixed cropping
- Avoid excessive nitrogen
- Resistant variants
- The stem rust fungus infects the plant through natural pores on the leaf surface, which are more vulnerable under low light intensity (such as the early morning or late afternoon) and prolonged periods of high relative humidity caused by frequent dews or rains.
Stem rust disease management in Wheat by chemical methods
- Spraying sulfur dusting at 35-40 kg/ha or 2g/lit Mancozeb.
- Fungicides manage rust diseases in wheat fields where disease pressure is intense.
- Fungicides that impede sterol synthesis [i.e., sterol biosynthesis inhibitors (SBIs) or demethylation inhibitors (DMIs)] are very effective.
- An integrated approach with a combination of preventive measures and biological treatments should be used to control fungi.
- Fungicides such as tebuconazole or prothioconazole can be applied for control. At the same time, triazoles and strobilurins can be used for preventive treatment.
- Some resistance to strobilurins has been observed.
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Preventive measures to control Stem rust disease in Wheat
- Grow wheat that is naturally resistant to the disease.
- Choose varieties that mature quickly.
- Plant as soon as possible in spring and as late as possible in autumn to avoid destructive conditions.
- Observe fields for signs of the disease.
- Get rid of weeds, volunteer plants, and any Berberis shrubs nearby.
- Use less nitrogen fertilizer.
- Keep plants spaced apart, so they get enough air.
- Remove and dispose of all plant remains to stop the fungus from surviving.
Conclusion
Stem rust is a severe wheat disease that can result in significant crop losses. Various control measures, including cultural practices, chemical treatments, biological control, and natural/organic methods, should be applied to manage stem rust effectively. Planting disease-resistant types, avoiding excessive nitrogen fertilizing, removing sick plant waste, and periodically checking fields are cultural practices.
Fungicides containing tebuconazole or prothioconazole are used in chemical treatments. In contrast, natural predators or pathogens of the rust fungus are used in biological management. Organic fertilizers, crop rotation, and companion planting are examples of natural and organic pest management approaches. It should be noted that fungicides should be combined with other management measures.
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