Classification of Plant Disease

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CLASSIFICATION OF PLANT DISEASE

• SUBMITTED BY
• SOMBIR KASHYAP
• MSC FINAL
• 5077

• SUBMITTED TO
• DR SUNDER SINGH ARYA
• PROFESSOR DEPARTMENT OF BOTANY MDU ROHTAK

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DEFINITION

• Plant disease an impairment of the normal state
  of a plant that interrupts or modifies its vital
  functions.
• Or
• A malfunctioning process that is caused by
  continuous irritation and produce symptoms.
• The organisms that cause disease are called
  pathogen.
• E.g. bacteria, fungi, viruses and protozoa etc.
• The study of disease condition is called
  pathology, also known as phytopathology

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Difference between healthy and diseased plant

• HEALTHY PLANT
• Normal physiological functions including
• Normal cell division, differentiation and
  development
• Absorption of water and minerals from the soil
  and translocation
• Photosynthesis
• Reproduction

• SICK /DISEASED PLANT
• A plant would not have all of these functions

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CLASSIFICATION ON THE BASIS OF CAUSE

• Infectious disease a disease that is caused by
  a pathogen that can spread from a diseased plant
  to healthy plant.
• Disease is caused by living organisms.
• It is also known as parasitic and biotic disease
• E.g. fungi, bacteria, virus, phytoplasma,
  nematodes, higher parasitic plants etc.
• Such as Pectobacterium atrosepticum (a potato
  pathogen)

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• Non-infectious disease disease that is caused
  by non-living organisms.
• Could not be spread to other healthy plant
• Such as factors
• Unfavourable environment e.g. frost injury,
  physiological wilt.
• Too low/high temperature
• Lack/excess of soil moisture
• Air pollution
• Nutrient deficiency- e.g. khaira disease in rice
  due deficiency of Zinc
• Mineral toxicity
• Soil acidity or alkalinity

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ON THE BASIS OF OCCURRENCE AND GEOGRAPHIC
DISTRIBUTION

• Endemic when a disease more or less constantly
  prevalent from year to year.
• These diseases are natural to one country or part
  of the earth.
• E.g. wart disease in potato in Darjeeling
• Epidemic such a disease occurs periodically but
  in severe state involving major area of crop.
• It may be constantly present in the locality.
• This is because the environmental conditions
  favourable for rapid disease development occur
  only periodically.
• E.g. rust, late blight, mildews.
• Pandemic
• E.g. late blight of potato
• Sporadic these diseases occur at very irregular
  intervals and locations and in relatively few
  instances.
• A given disease may be endemic in one region and
  epidemic in another.
• E.g. leaf blight, wilt.

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On the basis of natural perpetuation and mode of
infection

• Soil borne pathogen survive in soil or on
  infested plant debris lying in soil either as
  their resting spores or as mycelial strands and
  rhizomorphs.
• E.g. Root rot , wilt and seedling blight
• Air borne the micro-organisms are spread
  through air and attack the plants causing disease
  
• E.g. blight, rust, powdery mildew.
• Seed borne the micro-organisms are carried
  along with seeds
• E.g. damping off

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On the basis of symptoms

• Rust caused by Basidiomycetes of the order
  Uredinales
• Mostly attack on leaves and stems
• Appear as numerous rusty, orange, yellow, or even
  white-coloured spots that ruptured epidermis
• Some form local spots, swelling and even galls
• E.g. stem rust of wheat caused by Puccinia
  graminis, yellow or stripe rust of wheat , rye,
  and barley is caused P. striiformis, leaf rust of
  wheat and rye by P. triticina , leaf rust of
  barley , crown rust of oats , corn rust ,
  sugarcane rust , sorghum rust ,coffee leaf rust
  ( Hemileia vastatrix ) , cedar apple rust (
  Gymnosporangium juniperi ) etc

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Rust on wheat leaf, stripe,stem
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Rust on sugarcane leaf
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Coffee leaf rust
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• Smuts caused by a fungus of the order
  Ustilaginales.
• Many types of plant affected , but smuts are
  important in cereals and other grasses.
• They produce a mass of black , powdery spores and
  no grains are formed.
• The symptoms include the formation of masses of
  lack soot like spores and infected plant shows
  some degrees of distortions.
• E.g. loose smut of wheat and barley caused by
  Ustilago nuda tritici
• It is world wide in distribution
• In India, occurs in all states where wheat is
  grown, losses may be up to 40 per cent in some
  area.

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Smut in wheat and barley
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• Karnal bunt of wheat Mitra reported in 1930 and
  by 1985 also reported from W.B.,Gujrat, Bihar,
  M.P.
• Pathogen- Tilletia indica
• The disease is usually noticed only when the
  partly smutted and broken kernels are seen in
  threshold grain.
• Although infected wheat is not toxic to humans or
  animals, wheat grain containing more than 3
  bunted kernels is generally considered unfit for
  human consumption.
• Because the smut causes an unpleasant odour ,
  colour and taste in wheat product.
• All the spikes on a plant are not infected , and
  within a spike only a few spikelets are attacked
  .
• it becomes evident when the grains have
  developed.
• Grains have been partially, rarely wholly ,
  converted into bunt balls enclosed by the
  pericarp.

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Karnal bunt in wheat
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• Rots diseases that infect underground plant
  parts.
• They can be caused by fungi, bacteria or
  soil-borne nematodes.
• Infections lead to disintegration of underground
  tissues are difficult to manage because they are
  not visible.
• E.g.
• Rhizoctonia and Phytophthora are root rots.
• These two fungi attack the root system of many
  different plants.
• Bacteria can only enter the host tissue through
  wounds.
• Crown and collar rots occur at the soil line
  where the plant emerges.

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 crown rot infection on Beta vulgaris
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• Wilt a wilt disease is any number of disease
  that affect the vascular system of plants.
• Bacterial wilt of Cucurbits is caused by the
  bacteria Erwinia tracheiphila.
• Bacteria spread through the xylem vessels from
  the area of infection to the main stem and the
  entire plant wilts and dies.
• E.g. wilt disease in potato, tomato.

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bacterial wilt symptoms displayed by a muskmelon
plant
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Wilt in tomato
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• Canker a canker is a dead area in bark or
  cortex of woody stems.
• They are often large areas with definite margin.
• Dead bark splits and falls away.
• An example is citrus canker (bacterial)

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Citrus canker
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• Powdery mildew it is a fungal disease of
  foliage , stems, flowers and fruit where a
  superficial fungal growth covers the surface of
  the plant.
• E.g. grapes, cucumbers, grasses, soyabean etc.
• Symptoms white, powdery spreading patches of
  fungus on upper or lower surfaces, flowers and
  fruit.
• Sometimes tissue become stunted or distorted.
• Disease seldom kill their hosts but utilize their
  nutrients, reduce photosynthesis , increase
  respiration and transpiration and reduce yields
  by as much as 20 to 40.

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Powdery mildew of grape and soyabean leaves
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Powdery mildew of cucurbits
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• Downy mildew it is caused by family
  Peronosporaceae.
• Many ornamental and edible plants including peas,
  onions, lettuce, grapevines are affected.
• Main symptoms are discoloured areas on upper leaf
  surfaces white, grey or purple mould below.
• Timing is mainly summer and autumn, particularly
  in wet conditions.
• E.g. rose and lettuce.

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Downy mildew on rose and lettuce
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On the basis of organ they attack

• Root disease
• Shoot disease
• Fruit disease
• Foliage disease

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On the basis of host plant

• Cereal disease
• Vegetable disease
• Fruit disease
• Forest disease
• Ornamental disease

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On the basis of extent to which plant disease
associated with plant

• Localised these disease are limited to a
  definite area of varying extents of an organ, or
  only to a particular part of the plant.
• Systematic pathogen spreads throughout the
  entire plant to varying extents and is associated
  with almost every stage of plants life cycle.

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Based on pathogen generations

• Monocyclic disease those diseases which have
  only generation in one cropping season e.g. loose
  smut of wheat.
• Polycyclic disease those diseases which have
  more than one generation in a cropping season
  e.g. late blight of potato

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• References
• George N. Agrios , Plant pathology 5th edition
• R.S. Mehrotra , Plant pathology 2nd edition