Parasite is one which live on another plant gets food and shelter from it and causes harm or disease to is which is called hast. Puccimia graminis is parasite and is called rust. It is due to rustly colour of the spores which appear on the surface of hast. They are internal parasites and attack on angiosperes. Puccimia graminis belongs to class besides mycetes and subclass proto basidiomycetes and is characterised by four called basidium.
Basidia are separate and septa may be oblique, transverse or longitudinal. Besidiospores in per basidium are four. Puccimia graminis (black rust) is rust of cereals which affect wheat, oat, barley, rye and some wild grasses and produce condition called black rust. Puccimia passes its life cycle on two hosts which alternate each other. Hosts are tritium vulgare (wheat) and Berberies vulgaris (Barley). Hence puccinia is called heteroceous.
Life cycle of Puccinia graminis:
It is divided into five stages based on nature spores at particular stages. They are as under:
(1) Uredospores: Wheat is sown in October or November and the infection becomes in the month of February or March when elongate redish brown or black pustules appear on stem or leaf and the pustules are uredospores. Uredospores develop from branched and separate mycelium which is divided into many multicellular hyphae. Each cell of hypha is divided into several multicellular hyphae arranged in clusters, each hypha is called as Sporophore. They lie below the epidermis. Apical cell of sporophore enlarges and divides into an upper spore initial and lower basal cell. Basal cell forms stalk on elongation while spore cell form uredospore. Each spore is covered by another brownish wall exposure and inner delicate endospore. It has two nuclei and cytoplasm also, on maturation of uredospores the epidermis of host bursts and they are liberated in air uredospores germinate in favourable conditions and form germ tubes which infect other healthy wheat plants. thus rust disease get spread up through uredospores in the entire field of wheat.
(2) Teleutospores:- Later in April when wheat grains are maturing the uredia are going to produce few teleutospore. A pustule producing teleutospore is called s teleutospore or telium out wordly these appear as elongated black coloured streaks on the stem and leaf of wheat plant.
FIG 42 ABCD PAGE 94 & 95 FUNGI BY G.L.CHOPRA
This stage is called black stage or teleutostage of rust. They develop from multicellular hyphae having dikaryotic cells. Teleutospore is bicelled and spindle shaped. It is covered by exospores and endospores. Dikaryotic nuclei fuse together in teleutospore and form a diploid nucleus. Teleutospore, resist in unfavourable condition on maturation teleutospore and shut out by the rupture of epidermis and are carried to long distance by wind.
(3) Besidiospores:- Teleutospore after liberation fall off on soil and in the next spring season they germinate into a hyphal branch called epibasidium or promycelium. The diploid nucleus migrates into basidium and divides by reduction division to form four haploid nuclei. They come to lie at more or less equal distances. Septa appear between the nuclei dividing the basidium into four uninucleate haploid cells. From each cell arises a short stergima at the apex of which develop a basidiospore in which passes haploid nucleus. Basidiospores are small unicellular uni nucleate haploid and heterothallic in nature as mostly two of them represent positive (+) and the other negative (-) strain. The basidiospore are discharged by water droplet method with a force into the air. They are carried by wind to the leaves of the alternate host which is barberry (berberis vulgaris).
(4) Pycnidiospores:- Basidiosores which are unable to infect the wheat plant fall on the leaves of Berberis vulgarin. Each basidiosporeon germination form a primary hypha which penetrates into leaf cells and froms separate uninucleate monoploid branched myucelium. Few day after infection their monokaryotic mycelium results into formation of pseudoparanchymatous mass of tissue which forms pychidia or pynidial cup or spermatogomia. Few slender hyphae develop from this pycnidia which are uninucleate and are called sporophore. Nucleus of sporophore divides and one daughter nucleus after each division more towards the apex and transforms into a pycnidiospore.
Pynidiospore and formed in chains. Each pycnidiospore is a circular or oval thin walled structure. By the rupture of epidermis the pycnidiospores are liberated. Point of rupture is called as ostiole. Pycnidiospores are male sex organs which come out from ostiole. From the inner side of spermatogonial wall or pycnidiospore wall arise a large number of hair like sharp pointed periphysis. These project out by ostiole. A number of longer cylindrical and unbranched or branched hyphae with blunt tips arise just beneath or amont periphysis. They are respective hyphae or flexous hyphae and represent the female sex organs. They protrude through the ostiole.
(5) Accidiospore:- Monokaryotic mycelia which form pycnidiospores at the upper surface of leaf develop accidial cups on lower surface. The primary mycelium collects in patches near the lower epidermis of leaf and are known as protoaccidium. Due to the stimulus of sexual act the protoaccidium develops into a cup shaped accidium, from the bottom of which arise closely packed parallel chain of accidiospores on the side towards the lower epidermis. During the development of accium a basal layer of dikaryotic cells is differentiated nuclei travelling down the respective hyphae migrate from
Cell to cell of the primary mycelium through spectral perforations reach the basal cells of protoacecuim and thus dikaryotise them. These dikaryotia cells multiply and form the hymenium of aecidial cup while as subhymemium is formed of monokaryotic cells. A few sporophores emerge from dikaryotic hyphae which for a chain of binucleate or dikaryotic spores called as accidiospores, on maturation of aecuim spore chains push through the host epidermis and then by roof of pyridium, spores are thus exposed and dispersed by wind. The accidiospores are binucleate, subglobase to hexagonal, light orange yellow and with six germ pores. Aecidiospores from Barberry plant are carried by air to plans and infect the wheat plant on wheat plant the germ tube of accidiospores penetrate by stomata and gives side to dikaryotic mycelium from which urediospore arises. Thus the life cycle of fungus is completed.
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