Plant Athology

Branch of study Plant pathogen fungi, bacteria,virus, nematode & parasitic plant.
Plant Pathology is the science that studies the causes of plant diseases/ that deals with the interaction between pathogens and plants.
  • Most plant diseases around are caused by fungal or fungal-like organisms. However, other serious diseases are caused by viral and bacterial organisms.
  • Under favourable condition, interaction between host and pathogen results in plant diseases.
  • The signs and symptoms of plant disorders are the appearance of changes in the normal form and/or function of the plant. Signs are the physical evidence of damage caused by biotic or abiotic agents. Symptoms are the visible response of a plant to biotic and/or abiotic factors that result in a change or abnormality in the plant.
  • Some plant diseases are classified as “abiotic,” or diseases that are non-infectious and include damage from air pollution, nutritional deficiencies or toxicities.

diseases caused by the three main pathogenic microbes

Fungi

Fungi

Fungi are eukaryotic, achlorophyllous organisms that may reproduce sexually and asexually and whose filamentous branched somatic structures are typically surrounded by cell walls containing chitin.

Common sign and symptoms of funal diseases:

  • Leaf spot
  • Chlorosis (yellowing of leaves)
  • Sunken lesions
  • Damping off of seedlings
  • Rust on leaf, stem
  • White & grey mold
  • Powdery mildew
  • Birds-eye spot on berries (anthracnose)
  • Leaf blight
  • Concentric rings

Bacteria

Bacteria

Bacteria are microscopic, unicellular belonging to the prokaryotic group where the organisms lack a few organelles and a true nucleus.

Common sign and symptoms of Bacterial diseases:

  • Bacterial ooze
  • Water-soaked lesions
  • Bacterial streaming in water from a cut stem
  • Leaf spot with yellow halo
  • Fruit spot
  • Canker
  • Crown gall
  • Sheperd’s crook stem ends on woody plants.

Virus

Virus

Viruses are ultramicroscopic, nucleoprotein entities, non-cellular, microscopic infectious agents an obligate parasitic pathogens, which are less than 200 mμ in size.

Viruses can only replicate inside a host cell. Viruses can, in suitable cells, reproduce themselves from their genome.

A virus is often housed in a protein coat or protein envelope, a protective covering which allows the virus to survive between hosts and they contain only one type of nucleic acid either DNA or RNA never both.

As viruses have no ribosomes, mitochondria, or other organelles, they are completely dependent on their cellular hosts for energy production and protein synthesis.

Common sign and symptoms of Viral diseases:

  • Mosaic leaf pattern
  • Leaf curl
  • Crinkled leaves
  • Necrotic leaves
  • Plant stunting
  • Mottling of leaves
  • Growth distortion
  • Ring spots
  • Vein clearing
Rice Smut
Karnal Bunt In Wheat
Mango Antracnose
Chilli Antracnose
Potato Scab
Onion Smut
Tomato Bacterial Leaft Blight
Citrus Canker
Tomato Black Rot
Pomegranate Blight
Papaya Ring Spot
Potato Spindle Tuber
Tomato Black Ring
Tobacco Mosaic
Tomato Ring Spot

Lab work

  • Lab testing starts with Visual examination of affected plant material/samples with the help of Illuminated magnifier to detect mould growth, lesions, fungal fructifications, bacterial ooze/root galls and/ any characteristic virus symptoms.
  • Slide mounts are being prepared for microscopic examination including permanent mounts followed by labelling of slides and preservation of affected plant specimens (both wet/dry preservation).
  • Prepared slide is kept under Compound Microscope (10X, 40X, 100X and oil immersion) for identification of fungal spores.
  • Fungal spores are identified using morphological and conidial characters of various group of fungus using Stereo-zoom microscope fitted with camera.
  • Selective media is prepared based on pathogen identification and the infected sample is being isolated, cultured and incubated at specific relative humidity and temperature using BOD incubator and Humidity chamber.
  • Washing test is done using Wrist action shaker for identification of internal seed borne pathogens.
  • In case of bacterial identification, serial dilution technique is done for bacterial colony isolation and later using selective media, single colony is isolated and preservation is done.
  • Gram staining method is done for identification of gram positive/negative bacteria.
  • PDA plate method/grow out test/blotter paper method are most commonly done for fugal pathogen identification and isolation.
  • Molecular based identification of viral pathogen using ELIZA based techniques using ELIZA plate reader & ELIZA plate washer.
  • Deep freezing and storage of pathogen are done for documentation and future reference
Slide Preparation
Microscopic Observation
Selective Media Preparation
Glassware Sterilization
Pathogen Isolation
Blotter Paper Method For Fungal Isolation
Blotter Paper Method For Fungal Isolation
Incubation
Ooze Out Test For Bacterial Identification
Ooze Out Test For Bacterial Identification