Doc: Albugo Or Cystopus - Class 11 PDF Download

Note: Albuginaceae is a monotypic family. It includes only single genera Albugo.

It is an obligate, inter cellular parasite.

It cannot be grown on culture medium. It causes "White-rust disease in the plants of family cruciferae or brassicaceae. It shows specificity towards the host.

Etiology : - Study of causes of disease in body is called etiology.          

Characteristics of White-rust diesase : 

• White pustules/white blisters - They are usually present on lower surface of leaves which may also spread on the upper surface of the leaves & stems.
• The infected parts of the host become abnormal & the abnormality may be in the form of hypertrophy, fleshiness or distortion.

Note : 

(1)  The main reason of hypertrophy is the formation of sex organs in the intercellular spaces of host.

(2)  In the presence of less temperature and high moisture white rust disease spreads vigorously.

The study of spread of disease is called Epidemiology. 

Structure

Mycelium is branched, aseptate, coenocytic. (Septa are only formed in mycelium during reproduction). 

The hyphal wall is made up of cellulose.

Reserve food material is present in the form of glycogen and oil globules.

Hyphal network is found in the intercellular spaces of the host.

1. Round, button shaped or knob like and stalked haustoria are found in Albugo.
2. With the help of haustoria it absorbs nutrients from the host cells.

Structure of Hypha

In the apical region of haustorium dense cytoplasm, found but nuclei are absent.

The shape of haustorium have taxonomic importance.

It's mycelium is stained by cotton blue and mounted by lactophenol.

Reproduction

Reproduction methods

(1)  Asexual reproduction       

(2) Sexual reproduction          

Asexual Reproduction

1. It takes place by Conidia formation.
2. It is a type of sporangium or zoosporangium.
3. Conidium is a smooth colourless, spherical, thin walled and multinucleated structure, in which 3-8 nuclei are present.
4. The mycelium gives rise to erect branching. They are usually formed towards lower epidermis. They are called Conidiophore.
5. Conidiophores are unbranched and club-shaped structure. Their cell wall of the apical region is thin.
6. The thin walled apical region forms the chains of conidia by constriction technique.
7. Conidia are developed in basipetal sequence. It means newly formed conidia are present at the base of chain and old large conidia are present at the end of the chain.
8. A gelatinous disc is present in between the two conidia. It is called disjunctor.
9. This disc helps, conidia to remain in a chain. The chains of conidia grow and press the lower epidermis.
10. This causes epidermis to bulge out and appears in the form of blisters.
11. Due to more pressure, the epidermis bursts. And these conidia are spread in the form of white powder on the surface of leaf.

Dispersal & Germination

Conidia are dispersed by air.

Two different types of germination takes place in favourable conditions.

(i)   Direct germination :

• It takes place at high temperature and low humidity in the environment. eg. Albugo bliti
• Conidium absorbs some water which is present on the surface of the leaf. A germ tube comes out from the conidium. This tube enters inside host tissues through stomata and form intercellular mycelium.

(ii)  Indirect Germination :

• In the presence of less temperature approximately 10-15ºC and high moisture in atmosphere, condium germinates by (After 2-3 hours of their dispersal) zoospores formation.
• Conidium absorbs more water and swell up and forms 3-8 zoospores. These zoospores are enveloped by vesicle.
• These enveloped zoospores are ooze out then the vesicle dissolves and zoospores become free.

Free zoospores swim in water for few minute and finally they reaches on the surface of host, then after withdraw their flagella and round off and secretes a wall around itself.

Deflagellated zoospores with wall germinates through the germ tube. This germ tube enter into the host tissue through stomata or through the teared epidermis and form mycelium.

Structure Of Zoospores

Zoospores of Albugo are uninucleated, reniform or bean-shaped and biflagellated.

Flagella are located on the lateral side of zoospore which are unequal in length.

Out of them small the hairy flagellum is called Tinsel or Pantonematic or Flimmergersal.

1. Another long and smooth flagellum is called whiplash or Acronematic or peitgersal flagellum.

(i)   Monoplanetic Generation : - Only primary zoospores are formed.

(ii)  Polyplanetic Generation : - In which many generation of zoospores are formed, like primary, secondary and tertiary zoospores are formed. (during high availability of water)

Sexual Reproduction

1. Sexual reproduction is oogamous type.
2. Male and female sex organs are known as antheridium and oogonium respectively.
3. In A. candida the sex organs are generally formed towards the end of the growing season of the host.
4. Reproductive organs are endogenous. They develop in intercellular spaces, quite deep into the host tissues.
5. Their presence is externally indicated by hypertrophy and deformation of the organ.

  (i)   Antheridium : - 

• The antheridium is an elongated, club shaped and multinucleated structure.
• A transverse septum is present in its basal region. It develop on male hypha which is placed very close to the oogonium.
• There are many (6-12) nuclei present in a young antheridium but mature antheridium has only one functional nucleus.

(ii)  Oogonium : 

• Oogonium is globular in shape. The cytoplasm of oogonium differentiated into two distinct regions.
  (a)  Peripheral cytoplasm or Outer cytoplasm : -
• It is vacuolated, spongy and diffused. It is called periplasm.

(b)  Central cytoplasm : - 

• It is dense. It is known as ooplasm.
• Both Ooplasm and periplasm are multinucleated in the beginning but only a single nucleus remains in the ooplasm at maturity and rest of nuclei are transferred into the periplasm.
• However, some workers believe that all nuclei in the ooplasm except one disintegrate.
• A single nucleus present in the ooplasm is called female nucleus or oosphere.
• The oogonium of A.bliti, A.portulacae contains many female nuclei or oospheres.

Note :

 Antheridium and oogonium develops very close in the mycelium.

FERTILIZATION

A small protuberance develops from oogonium towards the antheridium. The wall of the antheridium and oogonium become thin at the region of their contact.

This outgrowth stimulate the antheridium for fertilization. The inner wall of stimulated antheridium produces fertilization tube which enters into the oogonium and grows until reaches the oosphere.

The terminal end of fertilization tube burst and introduces a single nucleus along with some cytoplasm.

Male nucleus fuses with the female nucleus and results in the formation of diploid nucleus. Now it is known as zygote.

Prior to fertilization a mass of protoplast is found in ooplasm. It is called coenocentrum. Which is formed by granular cytoplasm.

After the fertilization, zygote secretes a thick tri-layered wall around itself and now it is called oospore (2N).

1. In oospore there occur free nuclear divisions and 32-nuclei are formed in oospore (According to modern mycologists).
2. According to old mycologists, the diploid nucleus of the oospore divide first by a meiotic division, followed by several mitotic divisions resulting in the formation of about 32 nuclei in oospore.
3. Oospore with 32 nuclei is the resting stage of Albugo.
4. In this stage it lives on dry branches in the absence of host.

On returns of favourable conditions the 32 nuclei of oospore undergoes repeated divisions to form 100 or more nuclei.

100 or more zoospores are formed from these nuclei. The zoospores are released/liberated with vesicle by the rupturing of outer thick wall of oospore (formed by inner wall of oospore).

These zoospores are coming in contact with a suitable host (seedling plants) settle down on the host and infect them.

The initial stage of the disease during the growth period is called primary infection and it takes place through the soil born oospores.

According to Stevens all the structures of Albugo are diploid except gamete.

According to Sansome and Sansome meiosis division takes place at the time of gamete formation i.e. gametic meiosis found in Albugo. In Albugo meiosis not takes place in oospore.

Control Of White Rust Disease

1.   By crop rotation : - Primary infection can be checked through the growing of crops one after another crops. This is the best method to control the white – rust.

2.   By removal of infected plants from the field. Through this it can be eradicated.

3.   By application of fungicides – Such as – Bordeaux mixture. It is composed of

 CuSO₄        +      Lime water

 (1                 :                   1)

• Through the sulphur dust etc.
• In the absence of host Albugo grows on another plant (Cleome viscosa). This plant grows as weeds.

Note :

• Albugo never infects the underground parts of the plants such as roots.
• It infects only aerial parts of the plants.
• An excessive enlargement of diseased organ due to an excessive enlargement of cells, called hypertrophy.

Life Cycle

Diplontic type (according  to modern mycologists)/ Haplontic (According to old mycologists)