CPRT

• Pathogen


  An entity, usually a microorganism, that causes disease; disease-causing organism
• Plant pathogen


  Pest that causes disease in plants/crops, hampering growth and reducing yield
• Types of plant pathogens

  • Fungi
  • Bacteria
  • Nematodes
  • Viruses
• Annual world average crop loss is between 31-42%, with an average of 36.5%
• 10.1% of crop loss is due to insects; 12.2% due to weeds; 14.1% due to diseases resulting in $220 billion loss (data based on 8 major crops)
• In the US, there is a $9.1 billion loss annually despite adequate control
• In developing countries, higher values of crop loss may result in total crop loss if left uncontrolled
• Plant Pathology


  Scientific study of plant diseases
• Phytopathology


  Study of plant diseases
• Plant Pathology as a science

  • Deals with nature, characteristics, causes, development, control
• Plant Pathology as an art


  • Application of knowledge learned from the science for diagnosis, assessment, forecasting, formulation/recommendation of control, implementation of control
• Economic Importance of Plant Disease

  Reduction in quantity of food and commodities, loss of quality of produce, endangered safety of food due to toxic compounds, reduction of population of plant species, greater environmental hazards due to toxic chemicals in disease control, increased costs of production and food and product handling, further post-harvest losses during transport and storage, predisposition to attack by other pathogens
• Examples of diseases causing reduction in food quantity

  • Potato late blight caused by Phytophthora infestans, brown spot of rice caused by Bipolaris oryzae, coffee rust caused by Hemileia vastatrix
• Other important diseases


  • Coconut cadang-cadang due to cadang-cadang viroid, tungro disease of rice due to rice tungro spherical and bacilliform virus transmitted by greenleafhopper, downy mildew of corn caused by Peronosclerospora philippinensis, bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae, abaca bunchy top caused by abaca bunchy top virus, Panama wilt disease of banana caused by Fusarium oxysporum f.sp. cubense, Tropical Race 4
• Examples of diseases causing loss of produce quality

  • Mango anthracnose due to Colletotrichum gloeosporioides, citrus scab caused by Sphaceloma ci
• Factors affecting the quality of produce

  • Changes in appearance, scars, blemishes, spots make produce unattractive and not pleasing
  • Disease reaction leads to unpleasant odor and flavor due to utilization of carbohydrates, proteins, fat content
• Common diseases affecting produce

  • Anthracnose in mango caused by Colletotrichum gloeosporioides
  • Citrus scab caused by Sphaceloma citri
  • Blue mold of oranges caused by Penicillium italicum
• Endangered safety of food caused by toxins in produce
• Toxins in produce


  • Aspergillus flavus in copra, corn, peanut leading to aflatoxin and liver cancer
  • Turkey X disease in farm animals fed with contaminated feeds leading to aflatoxicosis and liver cancer
  • Ergot disease of rye caused by Claviceps purpurea
  • Other mycotoxins from Fusarium sp., Penicillium sp., Aspergillus ochraceus toxic to humans and livestock
• Reduction of population of plant species
• Plant species decline due to disease

  • Dutch elm disease caused by Ophiostoma novo-ulmi
  • Chestnut blight caused by Cryphonectria parasitica
• Greater environmental hazards due to toxic chemicals in disease control
• Increased costs of production and food and product handling
• Further post-harvest losses during transport and storage
• Post-harvest losses due to diseases

  • Rotting of fruits and vegetables due to bacteria and fungi
  • Anthracnose of mango
  • Soft rot of vegetables caused by Pectobacterium carotovorum pv. carotovorum
  • Mango anthracnose caused by Colletotrichum gloeosporioides
• Predisposition to attack by other pathogens
• Weakness due to disease leading to susceptibility to other pathogens

  • Nematode infection of roots leading to Fusarium, fungal, and bacterial infections
  • Feeding injuries becoming avenues for other pathogens
• YOLANDA DC. MANGAOANG: 'Associate Professor Department of Pest Management'
• Lesson 3.2. Disease Concepts, Symptoms and Signs, and Diagnosis of Plant Diseases
• Disease concept


  • An accurate definition is a prerequisite to understanding this phenomenon and formulation of control measures
  • A healthy plant can carry out its physiological functions to the best of its genetic potential
• Definitions of disease


  • An abnormality or deviation from the normal, an alteration, disorder, impairment, malfunctioning, disturbance, injury, or malady
• Diseased condition


  • The morphological effects, i.e. the symptoms constituting the plant’s response to the abnormal functioning
  • Result from disturbance of physiological processes: photosynthesis, respiration, translocation, root absorption, transpiration, etc.
• Cause of the disease

  • Biotic agents referred to as pathogens
  • Abiotic agents - Unfavorable environmental/physical factors (outside the optimum range of conditions necessary for plant growth)
  • Some authors refer to these as stresses
• Disease is dynamic in nature


  • Considered as a process resulting from continuous irritation of an agent; develops over time
  • Differs from injury which is instantaneous
  • Injury is required for disease to take place, but may or may not lead to disease
• Agrios (2005): 'defined disease as “the series of invisible and visible responses of plant cells and tissues to a pathogenic organism or environmental factor that result in adverse changes in the form, function, or integrity of the plant and may lead to partial impairment or death of plant parts or of the entire plant.”'
• Symptoms and Signs of Plant Disease

  1. Symptom- manifestation of a diseased condition

  2. Kinds of Symptoms: Localized= limited area (spots, galls, rots), Systemic= wide coverage (wilting, yellowing, blight), Primary= direct result of invasion (spots), Secondary= effect on distant or uninvaded parts (wilting, chloro
• Absorption


  Wilts- translocation
• Fruit rots or flower drop

  Reproduction
• Kinds of Symptoms


  • Localized= limited area (spots, galls, rots)
  • Systemic= wide coverage (wilting, yellowing, blight)
  • Primary= direct result of invasion (spots)
  • Secondary= effect on distant or uninvaded parts (wilting, chlorosis)
  • Microscopic= can not be seen by naked eye (enlarged cells)
  • Macroscopic= large to be visible (tumor, spots, chlorosis)
  • Histological= microscopic; requires dissection of tissues for microscopic examination
  • Morphological symptoms= change in form, structure; usually visible by naked eye
• 4 categories of symptoms

  • Pre-necrotic or plesionecrotic= preceding death of cells (wilting; hydrosis; yellowing)
  • Necrotic= death of cells, tissues, organs (rotting, spots, scab, mummification)
  • Hypoplastic= inhibition of differentiation, growth, & development (dwarfing, stunting, chlorosis)
  • Hyperplastic= overdifferentiation, overdevelopment, overgrowth of cells, tissues, organs
  • Hypertrophy= abnormal increase in size (galling, knots, tumors)
  • Hyperplasia= abnormal increase in cell number (galling, knots, tumors)