Puccinia Life Cycle

Dr. Neeraja Tutakne, Assistant Professor in Botany, SIES (Autonomous) College, Sion (West), Mumbai. Semester – V – Paper – I – Unit – III – Fungi LIFE CYCLE OF PUCCINIA Rust is a fungal disease of grasses and many other plants which appear on the host plant surface in the form of small coloured (red, brown, yellow, orange/black) pustules. There are three types of rust disease reported in Wheat plant, viz., Black rust, Brown rust and Yellow rust. Black rust is also known as stem rust of wheat and is caused by Puccinia graminis. Brown rust is also known as leaf rust of wheat and is caused by Puccinia recondita. Yellow rust is also known as stripe rust of wheat and is caused by Puccinia striiformis. Life cycle of Puccinia graminis triticii Puccinia graminis tritici is macrocyclic rust as its life cycle involves all the four types of spores. It is heteroecious rust as its life cycle is completed on two different host plants. The rust is obligate parasite. Life cycle on primary host or wheat plant: On wheat plant, infection is externally seen because of vertically elongated, reddish brown or blackish pustules (sori) on stem and leaves. The first pustules appear late in the spring and are reddish brown. Since they contain only uredospores, they are called uredosori. Puccinia Rust: A. Uredosori on wheat leaf B. Teleutosori on wheat stem Young uredosorus consists of a layer of binucleate basal cells which elongate vertically and divide transversely. The inner daughter cell called foot cell does not divide further. The outer cell divides transversely again. The upper cell forms uredospore and the lower cell forms the stalk. The uredospores mature within 10 to 12 days after infection. The mature uredospores become detached and are carried away by wind to other healthy wheat plants. A uredospore is broadly ovoid, one celled, binucleate (both the nuclei are haploid), thick walled and with four or five thin areas called germ pores. It germinates within a few hours after falling upon a suitable host plant (wheat) and sends out a germ tube through a germ pore. The germ tube grows over the epidermis of the host and when it reaches the stoma; its tip develops into a vesicle called appresorium. The binucleate protoplast enters the appresorium and a septum is formed at the base of the appresorium so that the empty germ tube is cut off from it. The appresorium then sends downwards a wedge like outgrowth whose distal end enlarges to form a vesicle after it 1  Dr. Neeraja Tutakne, Assistant Professor in Botany, SIES (Autonomous) College, Sion (West), Mumbai. Semester – V – Paper – I – Unit – III – Fungi has grown through the stomatal slit. The contents of the appresorium migrate into the vesicle developed beneath the stoma and the vesicle develops into branched, binucleate mycelium. This is secondary mycelium. The growth of the mycelium is intercellular and with the formation of many short haustorial branches which penetrate the host cells. The binucleate cells of the mycelium develop into uredospores as described earlier. Several successive generations of uredospores may be formed during the summer if conditions are favourable. T. S. of Wheat leaf passing through Uredosori At the end of the summer the same mycelium starts producing teleutospores instead of uredospores. The development of teleutospores depends upon photosynthetic activity of the host plant. During the process, the binucleate basal cell elongates vertically and divides transversely to form two cells. The inner daughter cell is called foot cell which does not divides further. The outer daughter cell divides transversely again. The lower cell forms stalk cell while upper cell divides transversely to form two binucleate cells. The two haploid nuclei in each cell unite form diploid nucleus. The teleutospore thus formed is two celled and each cell has a single diploid nucleus. The two cells of teleutospores act as hypobasidia and each secretes a highly thick wall with a single germ pore. 2  Dr. Neeraja Tutakne, Assistant Professor in Botany, SIES (Autonomous) College, Sion (West), Mumbai. Semester – V – Paper – I – Unit – III – Fungi T. S. of Wheat leaf passing through Teleutosori Life cycle on secondary host or barberry plant: The teleutospores do not germinate till the next spring. At this time they may be lying on the ground or may still be attached to dead host plants. One or both hypobasidia germinate to produce one tubular epibasidium each. The diploid nucleus of each hypobasidium moves into epibasidium and divides meiotically to produce four daughter nuclei. Transverse walls are formed after first and second division to form four haploid cells. Each of these four cells produces lateral sterigma which in turn produces haploid basidiopore. Of the four basidiospores thus produced, two are of positive strain and two are of negative strain. They are incapable of infecting wheat plants and they can develop into mycelium only if they fall on barberry leaves. Germination of teleutospore and formation of basidia with basidiospores A basidiospore falling on barberry leaf germinates to produce primary mycelium which has uninucleate cells. About the fourth day of the infection, the thick mat of primary mycelium is formed between the upper epidermis and palisade tissue. It 3  Dr. Neeraja Tutakne, Assistant Professor in Botany, SIES (Autonomous) College, Sion (West), Mumbai. Semester – V – Paper – I – Unit – III – Fungi produces spermogonia (pycnia). Each mature pycnium is flask shaped with an opening called ostiole at its apex. Hyphae adjacent to ostiole develop into straight pointed periphyses which project beyond the ostiole. Some of the hyphae give rise to receptive hyphae projecting beyond the periphyses. The cavity of the pycnium in internally lined with a palisade like layer of elongated uninucleate cells called spermatiophores each of which cuts off spermatia in succession. The spermatia are extruded through the ostiole and accumulate in a mass just outside it. At the same time, pycnium secretes a drop of nectar like fluid that covers periphyses, receptive hyphae and spermatia. T. S. of Barberry leaf passing through Pycnidium A primary mycelium also produces a mass of hyphae just within the lower epidermis. This mass called protoaecidium has a more or less plate-like layer of basal cells and a mass of displacement cells below it towards the lower epidermis. At this time spermatization takes place, i.e., spermatia from a mycelium of one strain are received by the receptive hyphae of the opposite strain. The haploid nuclei of the spermatia of opposite strain enter the receptive hyphae, migrate from cell to cell of the primary mycelium. This is possible because of the central pore in the cross walls between the cells. The migrating nuclei eventually reach and dikaryotize the basal cells of protoaecidium. If spermatization takes place then only there is development of protoaecidium into aecidium. Each of the dikaryotized basal cells cuts off a chain of dikaryotic cells towards the lower epidermis of the host. This chain grows into a cavity formed by the disintegration of the displacement cells. The basal cells at the periphery do not divide, but they mature into a protective layer called peridium. The derivatives cut off from all the other basal cells immediately divide into a large and a small daughter cell. The large cell becomes binucleate aecidiospore and a small cell disintegrates. A developing aecidium elongates and pushes through the lower epidermis. The apex of the peridium eventually ruptures and the exposed aecidiospores are liberated out. They are incapable of infecting barberry plants. The aecidiospores, if lodged on the wheat plants, germinates to produce binucleate mycelium which in turn produces uredospores. 4  Dr. Neeraja Tutakne, Assistant Professor in Botany, SIES (Autonomous) College, Sion (West), Mumbai. Semester – V – Paper – I – Unit – III – Fungi T. S. of Barberry leaf passing through Aecidium Systematic position Division: Eumycophyta 1. Definite cell wall throughout all the stages of vegetative development. 2. Plant body is mycelium which is with or without septa. 3. If septate, cells are mono, di or polykaryotic. Class: Basidiomycetae 1. Mycelium is septate, monokaryotic (primary) or dikaryotic (secondary). 2. Four basidiospores are produced exogenously on the basidium. Subclass: Heterobasidiomycetae 1. Basidium is differentiated into hypo and epibasidium which is usually septate. Order: Urediniales 1. Obligate parasite on vascular plants. 2. One to many celled teleutospores. 3. Four types of spores are produced, viz., uredospores, teleutospores, basidiospores and aecidiospores. Family: Pucciniaceae 1. Micro or macrocyclic rust. 2. When single host is required, the life cycle is autoecious and when two hosts are required, the life cycle is heteroeceous. Genus: Puccinia 1. Macrocyclic rust. Species: graminis 1. Infects plants of family Graminae. Variety: trticii 1. Infects wheat plants. 5