CLASSIFICATION OF PUCCINIA (RUSTS)
Kingdom :- Mycota
Division :- Eumycota
Sub-division :- Basidiomycotina
Class :- Teliomycetes
Order :- Uredinales
Family :- Pucciniaceae
Genus :- Puccinia
Species of Puccinia are known as Rusts, because the infected parts look like rusted iron. Rusts are known from very ancient times, because of the enormous loss caused by them to the crop. In ancient Rome, cereal rust diseases were thought to be caused by two Gods, Robigus and Rohigo. To please these Gods, the ancient Romans used to annually celebrate a festival, Robigalia.
The fungus is an obligate parasite. Some of the hosts as wheat, bajra, etc., are cultivated for their grains. The fungus can be collected from the wheat fields in February-March in Northern India. Berberis and Thalictrum are common weeds on hills. The former is a bush, whereas the latter is a large herb. Launea is very common as a weed in the fields and lawns. The fungus on Launea can be collected in March-April.
STUDY OF HOSTS, DISEASES AND THE SYMPTOMS
All the species of Puccinia are obligate parasites on some of the important cereals (fam. Grarninae or Poaceae) viz. wheat, maize and oat, on millets as bajra and jowar, and on other plants as Berberis and Thalictrum, etc. All the species of Puccinia are polymorphic. Some species such as P. graminis are heteroecious (i.e. they complete their life cycle on two different hosts), while others such as P. Butleri are autoecious (i.e. those which complete their life cycle on one host only). In almost all the heteroecio is rusts, uredo- and teleutostages are found on primary host while pycnidial and aecidial stages are found on alternate host. Some of the hosts, their causal organisms and diseases are as follow:
- P. grammls tritici and P. striiformis (=P.glumarum) infect wheat (Triticum sp., vern. gehun), the primary host and barberry (Berberis sp.; fam. Berberidaceae), the alternate host. They cause Black rust or Stem rust and Yellow or Stripe rust respectively on wheat. The symptoms of the disease are seen on leaves, leaf sheaths and sometimes on stem also. The floral organs are generally not affected (cj. Ustilago). In Black or Stem rust, (P. grammls tritici) dark brown or black, oblong to linear lesions are produced on leaves, leaf sheaths and stems which in case of severe infection, coalesce to form large patches. Yellow or stripe rust (P. striiformis = P. glumarum) is chiefly confined to leaves but if the attack is severe it may also spread to leaf sheaths and stalks. As such the green colour of leaves fade”, producing long streaks on which small oval and lemon yellow lesions are found.
- P. recondita (= P. triticina) infects wheat, the primary host and Thalictrum sp. (fam. Ranunculaceae), the alternate host and causes Orange leaf rust of wheat. It shows round to slightly oblong, orange coloured irregularly scattered pustules or lesions or form clusters on the leaf blades. They are never found in rows or stripes. The alternate host, Thalictrum, shows small brown specks in clusters on leaves.
- P. purpurea parasitizes Sorghum (vern. jowar; fam. Graminae or Poaceae), the primary host and Oxalis (vern. khatti buti; fam. Oxalidaceae), the alternate host. The diease is known as Leaf rust.
- P. sacchari causes Leaf rust on sugarcane (Saccharum officinarum; vern. ganna; fam. Graminae or Poaceae).
- P. butleri, an autoecious rust, attacks Launea sp. (fam. Compo sitae or Asteraceae) and causes Leaf rust. In case of other Leaf rusts orange to black pustules are seen on leaves and sometimes also on leaf sheaths.
- P. pennisetti infects Pennisetum typhoideum (vern. bajra; fam. Graminae), the primary host and Solanum melongena (vern. baingan; fam. Solanaceae), the alternate host.
- P. coronata parasitizes oat (Avena sativa; vern. jaii; fam. Graminae or Poaceae), the primary host, causing Crown rust and Rhamnus (fam. Rhamnaceae), the alternate host.
STUDY OF VEGETATIVE STRUCTURE
- The mycelium is well developed, branched and septate. It is generally intercellular and sometimes shows globular haustoria also.
- The mycelium is called dikaryotic because it possesses two nuclei of different stains in each cell. (The description mostly applies to heteroecious rusts. The uredosori and telutosori are developed on primary hosts)
STUDY OF UREDOSORUS AND UREDOSPORES
- The uredosori or uredopustules appear as red, oval or lemon shaped lesions on the leaves and leaf sheaths.
- The uredosorus in section reveals the ruptured host epidermis due to the pressure of underlying uredospores.
- The (dikaryotic) intercellular and branched mycelium is aggregated beneath the epidermis.
- The uredospores are produced in massive groups from this mycelium.
- Each uredospore is binucleate, stalked and rounded or oblong in shape.
- It has an outer exine which is finely verrucose or echinulate and an has inner smooth intine.
- Each uredospore has four equatorial germ pores.
- The uredospores get disseminated by wind and infect the fresh wheat plants.
STUDY OF TELEUTOSORUS AND TELEUTOSPORES
- The teleutosori or teleutopustules appear on leaves, leaf sheaths and stem as black, oval pustules that fuse to form patches in case of severe infection.
- A teleutosorus in a section reveals the (dikaryotic) intercellular, branched mycelium, a bunch of teleutospores and the ruptured host epidermis.
- The host epidermis is ruptured due to the pressure of underlying teleutospores.
- The teleutospores are formed by the same mycelium which earlier produced uredospores.
- Each teleutospore is borne terminally by the mycelium. It is stalked, elongated and bicelled structure.
- The apex of the teleutospore may be rounded or pointed as in P. graminis or it may be nearly flat as in P. recondita and P. striiformis.
- The teleutospore has a very thick but smooth exine and delicate thin intine. The exine turns black at maturity.
- At fIrst each of the two cells of the teleutospore is binucleate but later on, the nuclei fuse making each of them uninucleate.
- Each cell of the bicelled teleutospore has a single germ pore.
- The teleutospores are incapable of infecting the primary host (wheat plant). They germinate to form the basidiospores which infect the barberry plant or Thalictrum, etc., the alternate host. (The pycnidial anti aecidial cups are formed only on alternate hosts).
STUDY OF PYCNIDIAL CUP AND PYCNIDIOSPORES
- Each basidiospore germinates on the leaf of alternate host producing the (monokaryotic) mycelium, that ultimately forms the pycnicial cup or pycnidium.
- The pycnidia are generally present on the upper surface of the leaf and may be best studied in a transverse section of the host leaf.
- A mature pycnidium is flask-shaped with a pore known as ostiole at its apex.
- The hyphae near the ostiole are unbranched, pointed and orange coloured. These are called periphysis and project through the ostiole.
- Some of the periphyses are branched and thin walled. These are called’ receptive hyphae (or flexous hyphae). They project through the ostiole far beyond the periphyses.
- The cavity of the pycnidium is lined by many elongated and uninucleate pycnidiophores or spermatophores.
- The pycnidiophores are arranged in a palisadelike layer and each cuts off a chain of pycnidiospores or spermatia.
- The pycnidiospores or spermatia are discharged through the ostiole and help in producing the dikaryotic mycelium.
STUDY OF AECIDIAL CUP AND AECIDIOSPORES
- The aecidial cup or aescidium can only be formed by a dikaryotic mycelium.
- The aecidia are generally present on the lower surface of leaf and thus both pycnidia and aecidia can be seen in the same section of the host leaf.
- Each aecidium is cup-like structure with an outer protective layer called peridium.
- The developing aecidium elongates and is pushed through the host epidermis.
- At the base of aecidium there are many elongated cells known as sporophores, arranged in a palisade-like manner.
- Each sporophore cuts off alternately, a small and a large cell. The small cell is a disjunctor whereas the latter is the aecidiospore.
- In younger conditions, aecidiospores are hexagonal and are held in chains by the disjunctor cells. The spores round off as soon as they get separated.
- Each aecidiospore is a binucleate structure with a thick and smooth wall.
- The aecidiospores are blown away by wind and infect wheat plant (primary host). They are not capable or reinfecting barberry (the alternate host).
STUDY OF PUCCINIA BUTLERI
It is an autoecious rust, hence all the stages are found on a single host i.e. Launea sp., member of family Compositae. In this case there is no alternate host.
- KINGDOM – Mycota
- Chlorophyll absent
- Reserve food glycogen
- Cell wall of fungal cellulose.
- DIVISION – Eumycota
- A definite cell wall present.
- SUB-DIVISION :- Basidiomycotina
- Mycelium septate.
- Characteistic reproductive body, basidium.
- Basidiospores usually four, produced exogenously.
- CLASS :- Teliomycetes
- Basidiocarp lacking.
- Teliospores or chlamydospores in sori or scattered.
- Parasitic on vascular plants.
- ORDER – Uredinales
- Teleutospores formed terminally.
- Basidiospores on sterigmata.
- Infected plants rusty in colour.
- FAMILY – Pucciniaceae
- Teleutospores stalked.
- Teleutospores free or united but never in the form of a layer.
- GENUS – Puccinia
- Teleutospores bicelled.
- Aecia cupulate.