Diseases of wheat

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Stem rust of wheat
Black rust of wheat

Host (primary): Triticum aestivum (Bread wheat)
Host (secondary): Berberis vulgaris (Barberry)
Pathogen: Puccinia graminis f. sp.tritici

History

The disease is known to humans since the time of Aristotle (384-322 B.C). Ancient Romans seen a festival so-called Robigalia, in which they used to sacrifice red dog to the god of rust; the Robigus. They worshiped the god of rust in the spring in thought, if wheat destruction was caused by the rust.

Distribution

Throughout the human history the disease caused many epidemics in most of the countries of Asia, Africa, Europe, Middle East and America. The disease appears in severe form in southern, eastern and central India in destructive form. In rest of the Indian subcontinent the stem rust is sporadic and cause mild loss.

Pathogen

Puccinia graminis is obligate parasite with narrow host range. P. graminis was named by Persoon and five-spore stages was characterized by René and Tulasne in 1854. P. graminis has considerable genetic diversity and several special forms so-called forma specialis (f. sp.). Black or stem rust is caused by Puccinia graminis f. sp. tritici.

Puccinia graminis f. sp. tritici is heteroecious rust, that needs two hosts to complete its life cycle. Triticum aestivum (Bread wheat) is the primary host, while Berberis vulgaris (Barberry) is the secondary host. The disease is also called as macrocyclic rust, where five different types of spores are characterized. These are uredospore, teliospore (on primary host), basidiospore (in soil and debris), pycniospore and aeciospore (on secondary host).

Symptoms

On wheat

Wheat plants infected with black or stem rust

Upper surface of leaves showing uredosori

Lower surface of leaves
showing teliosori

Early symptoms appear as brick-red colored, elongated, blister-like pustules on the upper side of leaves. These are the uredosori consisting of uredospores. These appear on the leaf sheath, stems and glumes. Towards the end of the wheat growing season black colored teliosori are produced at the lower surface of the leaves. This gives the name ‘black rust.

On barberry

On the secondary host i.e., barberry small flask-shaped pycnidia in clusters are developed on upper side of the leaves. These pycnidia exude sticky honeydew. Pycnidia contain pycniospores. Five to ten days later, just below the pycnidia, aecial cups are produced at the lower side of leaves. Orange-yellow colored powdery aeciospores are born in the aecial cups.

Annual recurrence in north Indian planes

Annual recurrence of stem rust of wheat in north Indian planes was studied by Prof. K C Mehta. He studied that, uredospores do not survive the hot summers of north Indian planes and there no barberry plants in the region. Eventually the inoculum comes as uredopsores from the late grown wheat and barley in the hilly areas.

Control measures

• Eradication of secondary host (barberry) reduced the primary inoculum. Also, this practice disrupts the sexual cycle of fungus, which is the source of genetic variation.
• Cultural practices such as proper spacing, row orientation and fertilizer schedule are helpful in controlling the disease.
  Most effective method in controlling the disease has been genetic resistance. According to the “Karnal-based Directorate of Wheat Research” India has at least 22 varieties developed up to 2010, which are resistant to ‘Ug99 pathotype’ of black or stem rust. These varieties include DBW 17, PBW 550 and Lok 1.

Karnal bunt of wheat

Host: Bread Wheat (Triticum aestivum L.)
Pathogen: Neovossia indica (Mitra) Mundk = Syn. Tilletia indica Mitra

Distribution

The disease was first reported by Mitra in 1931 from a wheat variety (crossed between Federation 4 and Pusa 52 at Botanical section at Pusa) grown in Karnal (currently in Haryana district of Northern India). Since then the disease has been reported from India, Pakistan, Afghanistan, Nepal, Iran, South Africa, Brazil, Syria, Turkey, Lebanon, Sweden, Poland, Italy, Mexico, United States (Shukla et al., 2019). Bunt of wheat appeared as serious disease only during 1970s with introduction to the Mexican semi-dwarf variety of wheat. In India bunt of wheat is endemic in northern India from West Bengal to the western border including the tarai region. However, no significant loss occurs (personal observation during 2010s). Due to unfavorable conditions the states of Madhya Pradesh, southern Rajasthan, Maharashtra and Peninsular India are free from the disease (Shukla et al., 2019).

Symptoms

Bunted grain (left) healthy grain (right)

Bunted single spikelet of wheat 

Karnal bunt of wheat develops only when the wheat is matured. The disease is found sporadically in a susceptible plot and only few spikes are affected. In a spike only few spikelet (grains) are affected. In affected grains, only small portion is converted into black powdery mass, which is still enclosed in the pericarp. On thrashing black mass of spores come out and only a portion (usually embryo and grove) is destroyed leaving rest of the endosperm of smooth side unaffected. The powdery mass gives foul smell because of trimethylamine.

Pathogen

Karnal bunt of wheat is caused by Neovossia indica (Mitra) Mundk = Syn. Tilletia indica Mitra. Disease is seed, soil and airborne in nature. Black powdery mass are the teliospores, which germinate in the soil under favorable conditions (15 – 25 °C temperature and high soil humidity). These environmental conditions prevail during February to March in Northern India. Teliospores germinate to produce numerous sporidia, which is source of primary infection.

Control measures

• The disease is less notice and hard to manage, as it appears only at the maturity of wheat crops. Integrated Disease and Pest Management (IDPM) including host resistance, regulatory measures and cultural practices should be applied to control the disease.
• Seed treatment with Agrosan GN or Ceresan or Vitavax @ 2-2.5 g/kg seed eliminate the fungus.
• Excess irrigation at the time of flowering should be avoided, as high humidity favors the teliospore germination.
• According to Indian Council of Agricultural Research (ICAR) the new wheat variety PBW 502 is resistant to the Karnal bunt (www.business-standard.com, updated on January, 2013).

References

• Mitra, M., 1931. A new bunt on wheat in India. Annals of Applied Biology, 18(2), pp.178-179.
• Shukla et al., 2019. Karnal bunt disease of wheat: A review. International Journal of Research in Pharmacy and Pharmaceutical Sciences. 4(1) 16-18.
• https://www.business-standard.com/article/markets/study-identifies-wheat-strain-free-of-karnal-bunt-103102801128_1.html (accessed on 18 Apr. 20)

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Content first created on 30-08-2020
last updated on 26-09-2024