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causes of plant disease


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  • 2. OUTLINE Abiotic factors nutrients, pesticide exposure, environment pollution, temperature, moisture, & light. Biotic factors fungi, bacteria, nematodes, parasitic plants & virus
  • 4. 1) Nutritional abnormalities  Often nutrient abnormalities show up as discoloration of foliage  Common discoloration symptoms include:  Yellowing Chlorosis  Two types    Nutrient deficiencies Mineral toxicity
  • 5. Nutrient deficiencies  Plants require several major (N,P,Ca,Mg) and minor (iron,copper,Zn) elements for normal growth.  Deficiency or lack of any of these essential nutrients results in disease symptoms in the plant.  The symptoms in this photo occur due to a lack of molybdenum (minor plant nutrient)
  • 6. Mineral Toxicity  Presence of excessive available amounts of certain minerals in the soil can lead to mineral toxicity to the plants.  The extent of injury depends on the mineral, its concentration & species of the plant.  The plant in this photo has received excess manganese, which has proved toxic and led to yellowing.
  • 7. 2) Pesticide Exposure Some pesticides , if improperly used can cause serious damage to plants.  However, the most common type of chemical injury to plants is due to soil residue or spray drift of herbicides.  Examples of pesticide toxicity are:    2,4-D damage to beans and tomatoes Glyphose (Roundup) damage to fruit trees
  • 8. The common symptoms of herbicide exposure are curling and cupping  This plant was exposed to the herbicide 2,4-D 
  • 9. 3) Environmental Pollutants High level of fluoride in water or fluorine gas in the air can cause symptoms like this.  The damage is concentrated towards the margins of the leaf where fluorine tends to accumulate.  E.g. Air pollution 
  • 10. Air pollution  Certain chemicals such as O3, SO2 and NO2 are released into the air from factories, power plants and automobile exhausts.  These chemicals can accumulate in the atmosphere insufficient concentration to cause damage to plants.  Ozone damage appears in the form of chlorosis, spots and bleaching of young leaves.   This common in certain regions of the country where there is a high ozone concentration in smog Some of the air pollutants responsible for acid rain cause damage to vegetation in certain regions.
  • 11.  Ozone damage on morning glory  Ozone damage or marijuana leaves
  • 12. 4) Extreme Weather Conditions Extreme of weather can also lead to plant injury. Cold injury  Low temperature, like frost or freeze can damage the exposed or sensitive organs (buds, flowers, young fruits) or may kill the entire plant.  As the new branch tips began to expand, a period of cold was severe enough to kill the growing tips. Heat injury  In this case the temperature was high enough and damage the plant tissue  When plants or plant parts are exposed to high temperature for prolonged periods, symptoms of scorching or scalding may develop. 
  • 13. 5) High/low soil moisture Due to excessive watering poor drainage or flooding may cause plants to turn yellow and be stunted.  Potted indoor plants may show poor development or root rots.  At the other extreme, low moisture or drought conditions can lead to poor development, wilting and death of plants. 
  • 14. 6) high/low intensity   High light intensity is usually not a problem but low light conditions, especially for indoor plants, lead to etiolation (tissue are yellowish) A normal and etioled shoot under sun and artificial lighting.
  • 16. 1)Fungi Largest pathogen group  More than 8000 pathogenic species  Vegetative growth through production of hyphae  Reproductive via spores 
  • 17. Fungal Hyphae
  • 18.    Some examples of plant diseases caused by fungi: brown rot of cherries, peaches and apricots; apple scab. powdery mildew of roses, apples and other plants.
  • 19. Brown rot powdery mildew (Monilinia fructicola) (Triticum sp.)
  • 20. 2) Bacteria About 200 pathogenic species  Can be seen with a light microscope  Simple, unicellular  Reproduce by binary fission 
  • 21.    Some of the commonly encountered bacterial diseases are: crown gall of rose, grape, apple, cherry and other ornamental plants fire blight of apple and pear
  • 22. Crown Gall Fire Blight (Agrobacterium tumefaciens ) (Erminia amylovora)
  • 23. 3) Viruses     Can only be seen using an electron microscope Extremely simplenucleic acid with a protein coat. Reproduce by taking over host reproductive machinery Often associated with insect vectors.
  • 24.   Viruses can multiply only in a living host cell and can often spread systemically throughout the infected plant. Viruses may be transmitted from infected to healthy plants mechanically, through grafts, or contaminated propagating material; however, the most important means of spread is by insect transmission.
  • 25. Viruses cause mainly two types of symptoms: mosaics and leaf curls.  Some examples:    rose mosaic potato leaf roll
  • 26. Rose mosaic (Rose Mosaic Virus) (RMV) Potato leaf roll (Polerovirus)
  • 27. 4) Nematodes Parasite worms  Very complex compared to other pathogens  Usually seen only with a light microscope  Reproduce by eggs. 
  • 28.     Most of the nematodes feed on the underground parts of the plants (roots, tubers, bulbs, etc.) causing lesions or root knots. Some examples: Root knot nematodes on tomato, potato, beans and many other plants. Stubby root nematode of corn, onion.
  • 29. Root knot nematodes (Meloidogyne) Stubby root nematode (Trichodoridae)
  • 30. 5) Phytoplasmas      A prokaryotic organism that lacks a cell wall and survive in the phloem of plant The helical phytoplasmas are known as spiroplasmas. Round or elongate Usually seen only with an electron microscope Reproduce by binary fission
  • 31.   Some of the commonly encountered phytoplasmas diseases: aster yellows phytoplasma on carrots, tomatoes, onions and lettuce.
  • 32. Aster yellows phytoplasma