Plant Path L1-10

• Plant pathology


  Scientific study of plant diseases, what causes them, how and why they occur, and how to manage them
• Plant pathology


  • As a SCIENCE: Nature/properties, Causes, Factors affecting disease development, Ways to control or manage them
• Plant pathology


  Study of plant pathogens and diseases they cause in plants
• Main components of plant pathology

  • Mycology - fungi & fungal-like oomycetes
  • Bacteriology - typical bacteria, fastidious bacteria, mollicutes (e.g. Phytoplasma and Spiroplasma)
  • Nematology - nematodes
  • Virology - virus and viroids
• Late blight of potato caused famine
• Ergotism caused deaths of thousands of people
• Coffee rust have changed the way people behave and/or their customs
• Southern corn leaf spot, chestnut blight, and dogwood anthracnose epidemics caused damage resulting to crop loss amounting to millions of dollars
• Great Irish Famine


  Potato late blight epidemic in Europe (1845) led to more than a million people starving to death due to almost total destruction of the potato crop
• Symptoms of potato late blight

  • Water-soaked lesions on the leaves
  • Rotting of leaves & stems
  • Rotting of tubers
• In the past, plant diseases were thought to be manifestations of the wrath of God, and there was no disease control due to lack of knowledge about the cause of the disease
• Although the microscope was invented in 1674, little progress was made toward the concept of microbes as the cause of disease for 200 years
• Heinrich Anton de Bary

  German doctor and botanist, Father of Mycology who started the scientific study of plant diseases; proved that the spores caused the disease
• Structures of Phytophthora infestans

  • Oospores
  • Sporangia & Sporangiophores
• Ergot of Rye


  Caused by Claviceps purpurea, sclerotia-hard survival structures shaped like the spur of the rooster
• Ergotism


  Caused by eating rye bread contaminated with sclerotia of Claviceps purpurea, which contain alkaloids with a strong hallucinogenic effect. Symptoms include tingling of extremities, high fever, hallucinations, mental derangement, abortion, and loss of hands, feet, and legs due to restricted blood flow and subsequent gangrene, leading to death.
• Thousands of people died in Europe due to ergotism
• Coffee Rust


  Caused by the fungal pathogen Hemileia vastatrix, which struck Ceylon in the 1870s, resulting in the destruction of Ceylon's coffee trade
• By 1880, tea plants replaced 140,000 ha of the destroyed coffee trees in Ceylon
• Chestnut Blight


  Caused by Cryphonectria parasitica, which destroyed millions of chestnut trees in the northern Atlantic states in 1900, resulting in billions of dollars in lost timber
• Southern Corn Blight


  Caused by a T race of the fungus Cochliobolus heterostropus (Bipolaris maydis), which destroyed approximately 15% of the U.S. corn crop in 1970
• Corn Downy Mildew


  Caused by Peronosclerospora philippinensis, a major problem in the Philippines where losses in maize were estimated at 8% nationally in 1974-75, and can be as high as 100%
• Abaca Bunchy Top


  First observed in the Philippines in 1915, transmitted by the black aphid Pentalonia nigronervosa, caused by Banana bunchy top virus (BBTV) and Abaca bunchy top virus (ABTV)
• Rice Tungro


  First described in the Philippines as 'tungro' (degenerative growth), transmitted by green leafhoppers, caused by Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV), decimated 700,000 ha of rice in 1971
• Citrus Greening/Leaf Mottling/Huanglongbing


  First described in the Philippines and attributed to zinc deficiency, thought to be caused by a virus, transmitted by the psyllid Diaphorina citri, wiped out the citrus industry in Luzon, caused by Candidatus Liberibacter
• Coconut Cadang-cadang


  Premature decline and death of coconut palms, caused tremendous economic losses of $200M since it was discovered in 1908 in the Bicol, Quezon, and Samar regions of the Philippines
• Direct losses due to plant diseases

  • Reduction in yield
  • Reduction in quality of produce
  • Deterioration of produce during storage, marketing and transport
• Indirect losses due to plant diseases

  • Pre-dispose plants to the attack of other plant pathogens/pests
  • Increased agricultural inputs
  • Limits the kinds of crops to be grown in an area
  • Plant pathogens produce toxins detrimental to humans and animals (e.g. aflatoxin by Aspergillus flavus)
• Pathogen of Late blight of potato: Phytophthora infestans
• Pathogen of Ergot of rye

  Claviceps purpurea
• Pathogen of Coffee Rust

  Hemileia vastatrix
• Pathogen of Chestnut Blight

  Cryphonectria parasitica
• Pathogen of Corn Downy Mildew

  Peronosclerospora philippinensis
• Pathogen of Abaca Bunchy Top


  Abaca bunchy top virus
• Vector of ABTV


  Pentalonia nigronervosa
• Pathogen of Rice tungro

  Rice tungro bacilliform virus RTBV; Rice tungro spherical virus (RSTV)
• Causal agent of Citrus greening/ Leaf mottling

  Candidatus liberibacter
• Characteristics of a healthy plant

  * Carry out normal physiological functions
• Characteristics of a diseased plant

  * cannot carry out normal physiological functions

  * abnormal development of plants

  * reduces its economic value
• Disturbance in physiological process caused by a pathogen that result in changes in form, function, and integrity of plant

  Plant Disease