Rust of wheat or life history of Puccinia Dr. Anuj Rani Department of Botany, T.N.B. College (T.M. B.U., Bhagalpur-812007) [E- learning: B.Sc. Part -II Part-I, Botany Sub.] Introduction: Rust of wheat is the most important and destructive of all the plant disease. They are the potential causes of enormous economic losses in all wheat growing regions of the world. Rust diseases of wheat are among the oldest plant diseases known to humans. Three different forms of rust attack wheat in India: Black or stem rust caused by P. graminis tritici (Pres.) Leaf brown or orange rust caysed by P. recondita (Roxb.) Yellow or strip rust by P. striiformis west.
Black or stem rust of wheat Causal Organism: Puccinia graminis tritici (Pers.)Erikss & Henn. Systematic position: Wheat rust pathogens belong to genus Puccinia, family Pucciniaceae, order Uredinales and class Basidiomycetes. Puccinia graminis tritici (Pers.) Erikss & Henn usually does not appear on the wheat crop until late in the season. It is often not seen until March in northern India, Stem rust is also known as black stem rust. It is primarily a disease on wheat, though it can also cause minor infections on certain cultivars of barley and rye. Leaf rust is caused by Puccinia recondita tritici (now known as Puccinia triticina). Like the stem rust fungus, this pathogen is primarily a problem on wheat, but it may be weakly pathogenic on some cultivars of barley, triticale, and some species of goat grass and wheat grass Symptoms: 1) These diseases are each caused by a particular species of the “rust” fungus, Puccinia. The diseases get their name from their appearance on the plant. 2) Infection can occur on any above-ground plant part, leading to the production of pustules that contain thousands of dry yellow-orange to reddish-brown or black spores. These pustules give the appearance of “rust” on the plant. 3) Stem rust occurs primarily on stems but can also be found on leaves, sheaths, glumes and even seed. And developed a small circular to oval yellow pustules on infected tissue of the upper leaf surface. These pustules produce a large number of spores called uredosori or uredia. They very soon burst and expose a “orange- dust” on the leaf surface consisting of thousands of uredospores. The uredial pustules occur on stem, leaf sheath, leaves and ear heads but the stem is often most severely affected.
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4) In the late stages of the disease, teleutosori or telia produce. The teleutospores are often produced in the form of pustules. The pustules of black rust are reddish- brown in color and elongated in shape they are produce numerous black sooty spores as similar to uredosori they burst and expose a black bed of teleutospores. Severe infestations with many stem lesions may weaken plant stems and result in lodging. The name black rust was given to this rust due to the prominence of its dark black telia. 5) Chlorosis or yellowing of leaves can be quite evident with both leaf and stripe rust. 6) Rust spreads fast under relatively warmer and humid environmental conditions. Life cycle of Puccinia graminis tritici: Puccinia graminis tritici effects the wheat stem and causing the black rust / stem rust. Which is a internal obligate parasite found in associated with wheat growing areas. It is heteroecious fungus because they complete their life cycle on two host i.e. Wheat and Berberis sp. (barberry). Wheat plant is called primary host whereas barberry is the secondary host or alternative host. It is a macrocyclic and polymorphic rust. The life cycle of Puccinia is divided into five stages on the basis of nature of spores. Stages on primary host (1) Uridinial stage The dikaryotic mycelium is produced by the germination of aeciospores on wheat plant. It enters through stomata and developed in intercellular space of leaf, stem or glumes. Reddish brown pustules or sori appear on the leaf and stem of wheat in March. These sori are called uredosori. Uredosori contains numerous uredospores. These are globose and thick walled spores with long stalks. Each uredospore is one celled, binucleate with germ pore on its wall. The spores exert pressure on the underlying epidermis causing breakdown of the host epidermis to form uridinia and this stage is known as uridinial stage. Germination of spores: The spores germinate after falling on the wheat plant. It germinates and produced germ tube. The germ tube reaches the stomata and tip swells into the vesicle called appressorium which produces, septate and branched hyphae inside the leaf. Each cell of hyphae has two nuclei (dikaryotic). These hyphae develop haustoria and dikaryotic uredospores under the epidermis of leaf. The epidermis ruptures and form pustules. Wind transfers these uredospores to other plants of wheat.
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(II) Telial stage: Teleutospores are produced at the end of growing season of wheat (April, May) now colour of uredosori changes and become dark brownish to dark reddish or rusty colour. This colour is due to the production of new spores called as teleutospores. These spores are stalked, bi-celled, each cell contain two nuclei, thick walled, spindle shaped with tapering ends and one germ pore. As the teleutospore mature the two nuclei in a cell fuse to form a diploid nucleus. After maturity teleutospores also exert pressure on overlying epidermis and ruptured then spores are exposed. They are dispersed by wind and fall on soil. They do not germinate until the next spring.
Fig ( A) V.S of leaf passing through teleutosorrus B) single Teleutotospore (C) germinating teleutospore (III) Basidial stage (on soil): Teleutospores germinates in the spring session on the soil. Each teleutospores produces a germ tube called promycelium or epibasidium. Both nuclei of each cells fuse to form diploid nucleus. These diploid nuclei undergo meiosis and form four haploid nuclei. Out of four two are positive (+) and rest two are negative (-) strain. Now promycelium divides into four cell by the formation of transverse septa and each cell produced thin wall structure called sterigma. Then haploid nuclei move into sterigma and forms different mating type of basidiospores.
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The basidiospores are one celled and uninucleate. Basidiospores discharged and disseminated by wind and can germinate only on the leaves of alternative host.
Fig: Germinating teleutospore with basidiospores Stages on Barberry Plant: Infection first starts on the dorsal surface of the leaf in the form of minute, dark coloured and flask shaped pycnia which appear as yellow spots. Beneath Pycnia, on the ventral surface, appear cup like projections of aecia or aecidia. (IV) Pycnidial stage or Spermogonium stage; Haploid basidiospores infect alternative host barberry. They fall on the leaf of barberry. They germinate to produce a small germ tube which may be (+) or (-) strain, depending on the strain of the basidiospores. The germ tube penetrates the cuticle and entre the epidermal cells of leaf. These cells produce monokaryotic hyphae in host cell.. These hyphae develop haustoria for absorption of nutrients. The monokaryotic hyphae of different strain form knots below the upper epidermis of leaf. The knot like mass of hyphae is changed into flask shaped called pycnidia or spermogonia they may be (+) or (-) strain, depending on the strain basidiospores. Spermogonium opens on the upper surface of leaf by a minute pore, called ostiole. The ostiole is guarded by a tuft of unbranched, tapering, sterile hairs known as paraphysis and fertile spermatiophores. Spermogonia form two structures: (a) Pycnidiospore: Small hyphae are produced inside the spermogonium called spermatiophores or pycniophores. These hyphae produce many small, haploid pycnidiospore or spermatia. It is small, oval, hyaline which may be (+) or
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(-) strain. Spermatia come out through ostiole. And passed on opposite strain of flexuous hyphae with the help of insects. (b)Receptive hyphae or Flexuous hyphae: which may be (+) or (-) strain. Many paraphyses come out through ostiole. Some of them act as receptive hyphae and carries opposite strain of pycnidiospore./ spermatia. Dikaryotization or spermatization: When a spermatium becomes attached to the opposite receptive hyphae, point of contact dissolved and spores nucleus transferred in side flexuous hyphae. Resulting a dikaryotic mycelium is formed from flexuous hyphae and produced protoaecidia. This pair of nuclei of opposite strains is called a dikaryon and this process is called Dikaryotization/ spermatization. Protoaecidia reach on lower surface of the leaf and develops into cup shaped aecidium.
Fig: A section through Pycni (V) Aecial or Aecidial Stage: The dikaryotic basal cells of the protoaecidium arrange themselves vertically beneath the lower epidermis and are called as sporophores. Each bi-nucleate basal cell then cuts off a chain of bi-nucleate cells in basipetal succession on the side towards the lower epidermis of the host. These cells are the aecidiospore mother cells (Fig. 7). These cells further divide transversely to form a large cell and a small cell. The large cell develops into aecidiospore while the small cell remains sterile and is known as disjuncture or intercalary cell. With the development of the aeciospores some of the bassal cells lying at the periphery of protoaecidium mature into a one-celled thick protective layer called peridium.
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This entire structure is cup shaped and is known as aecium. The developing aeciospores rupture the peridium by exerting a pressure on it. Thus, the aeciospores are liberated. They are unicellular, polyhedral, thin walled, bi-nucleate and orange yellow colored. Germination of Aecidiospore: The binucleate aecidiospores are carried by air currents to the primary host (wheat) on which they germinate and produced a germ tube or primary hyphae. Later it produced uredo and teleutospores respectively on wheat. In this way, the life cycle of Puccinia graminis is completed
Fig: T.S. of barberry leaf through pycnial and aecial cup
Fig : Life cycle of Puccinia graminis tritici
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Control Measures: • Grow rust-resistant varieties of wheat recommended for a particular area such as HD-2733, HD-2428, HD-2189, U.P.2425, PBW-343, HW-291, HW-2004, HS-240, VL-719 etc. Different varieties of wheat are sowing the total area it is safer than single • Avoid late sowing of late maturing varieties. Late sown crop is more exposed to rust damage. • Do not use excess nitrogenous fertilizers, as very high nitrogen dose favors rust development. Use of high dose of potash is known to reduce rust infection. Apply balanced doses of nitrogen and potash as recommended. • Damage by wheat rust may be minimized by spraying Zineb or Mencozeb 75 WP. Spraying is recommended only when a good crop of wheat is threatened by rusts. Spraying is not economical on a poor crop of wheat. Spray 0.2 per cent Zineb or Mencozeb 75 WP and 0.1 per cent Sandovit (spreader-sticker) as outlined below: ➢ Give first spray when rust pustules are seen. This normally occurs during the last week of January or first week of February. About 375 liters solution per hectare is enough for this application. ➢ Give second spray 10 days after the first. Use 750 liters solution per hectare. ➢ Give third and fourth sprays at an interval of 14 days. Use 1000 and 1250 liters solution per hectare, respectively.
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