Crop Protection 2

• Genetic manipulation of crops


  Adding a specific stretch of DNA into the plant's genome, giving it new or different characteristics
• Types of Genetic Modification Methods for Crops

  • Traditional Crop Modification
  • Genetic Engineering
  • Genome Editing
• Traditional Crop Modification


  • Traditional methods of modifying plants, like selective breeding and crossbreeding, have been around for nearly 10,000 years
  • Most of the foods we eat today were originally created using a combination of traditional methods
• Genetic Engineering


  • The deliberate modification of the characteristics of an organism by manipulating its genetic material
  • A method that enables scientists to copy a gene with a desired trait in one organism and put it into another
  • Genetic engineering has been used since the 1970s and builds on the scientific advances we have made in the study of DNA
• Genome Editing


  • The newest method that gives scientists more precise and targeted ways to develop new crop varieties
  • Genome editing tools can make it easier and quicker to make changes that were previously done through traditional breeding
• Types of Host Plant Resistance

  • Ecological resistance
  • Genetic resistance

  
• Ecological resistance


  • False or fake; also called pseudo-resistance
  • Resistance of the crop to pest infestation is due to the primary control of environmental factors
• Phenological asynchrony


  • The susceptible stage of the crop does not coincide with the peak of pest population
• Induced resistance


  • Responses of crop plants to normal practices done by farmers such as fertilization or irrigation
• Induced resistance


  • Application of silica (inhibit the penetration process of some pest into the host)
  • Plant receiving well-balanced nutrition is best equipped to withstand diseases
• Genetic resistance


  • Resistance of the crop to pest attack is under the primary control of the genetic factors
• Vertical resistance


  • Also called monogenic, major gene or specific resistance
  • Resistance is governed by one or few genes
• Horizontal resistance


  • Also called minor gene, field, partial or polygenic resistance
  • Resistance is governed by many genes
• Advantages of HPR


  • It is specific (only affects certain pest species)
  • It has a cumulative effect (effects last for many generations)
  • It is persistent (lasts for a long period of time)
  • It has a low initial investment
  • No additional cost to farmers
  • It is compatible with other control tactics
  • Not hazardous to the environment (no residue problem)
• Disadvantages of HPR


  • Require a longer time to produce or develop resistant varieties
  • Incompatibility of resistance with other agronomic traits/characteristics
  • Lack of resistance to polyphagous insects (e.g. cutworms, aphids)
  • Resistance of one pest is tied with susceptibility to other pests
• Insect plant resistance


  The use of resistance crop varieties to suppress insect damage
• Plant resistance


  The consequence of heritable plant qualities that result in a plant being relatively less damaged than a plant without the qualities
• Insect-resistant plant


  • One that yields more than a susceptible cultivar when confronted with insect pest invasion
  • Resistance of plants is relative and based on comparison with plants lacking the resistance characters

  
• Antixenosis/non-preference


  • Plants produce something that drive insects
  • It represents resistance in which the insect is either repelled by or not attracted to its normal host plant
  • Ability of a variety to repel insects causing a reduction in oviposition/feeding
  • Affects the behavior of an insect pest

  
• Antixenosis/non-preference


  • Color, thickness of the cell walls & plant tissues, surface wax on leaves, spines, thorns, trichomes
• Antibiosis


  • Represents resistance in which feeding on the plant causes mortality or the inhibition of growth, development, or physiological processes in the insect
  • Includes all adverse physiological effects of a temporary or permanent nature resulting from the ingestion of a plant by an insect
• Effects of Antibiosis


  • Death of the larvae
  • Abnormal growth rate
  • Failure to pupate
  • Failure of adults to emerge
  • Malformed or undersized adults
• Causes of Antibiosis


  • Toxic metabolites
  • Absence or insufficiency of essential nutrients
  • Unbalanced proportion of nutrients
  • Presence of anti-metabolites that renders some nutrients unavailable
  • Presence of enzymes that inhibit the normal processes of food ingestion & utilization
• Tolerance


  The plant can produce considerable yield despite supporting a population of pests due to the ability of plant to compensate the damage caused by insects
• Pre-existing Defenses


  • Pre-formed structural barriers that help limit pathogen attachment, invasion and infection
• Structural Barriers


  • Cuticular wax
  • Structure of epidermal cell walls
  • Size, location & shapes of stomata and lenticels
  • Thick-walled cells
• Basal resistance


  • Can be triggered when plant cells recognized microbe-associated molecular patterns (MAMPs) or PAMPS (pathogen-associated molecular patterns), including specific proteins, liposaccharides and cell wall components found in pathogen
  • Living plant cells become fortified against attack

  
• Local Acquired Resistance (LAR)

  Resistance around the point of necrosis caused by pathogen infection or by a chemical

  
• Systemic Acquired Resistance (SAR)

  • Resistance that spread systematically and develops in distal untreated parts of the plant which is non-specific and generalized resistance
  • Results in the plant showing enhanced resistance to subsequent infection

  
• Plant activators


  • Salicylic acid, arachidonic acid, 2,6-dichloroisonicotinic acid
• Structural Defenses


  • Cytological defense reaction
  • Cell wall defense structures
  • Histological defenses
• Cell wall defense structures

  • Thickening of cell
  • Callose deposition
  • Papillae formation
• Histological defenses


  • Formation of cork layers
  • Formation of abscission layers
  • Formation of tyloses
  • Deposition of gums at the infection sites
• Chemical Defenses


  • Production of antimicrobial substances in attacked cells
  • Phytoalexins
  • Toxins - antimicrobial substances produced in appreciable amounts only after stimulation by various types of phytopathogens or by chemical or mechanical injury

  
• Effector triggered immunity (ETI)


  Occurs when a plant recognizes a specific pathogen molecule after the basal resistance failed

  
• Hypersensitive response (HR)


  • Necrotic defense reaction; involves a rapid cell death of cells immediately surrounding the point of infection thereby walling off the pathogen and preventing its spread
  • Brought about by the recognition of the elicitors/effector of the pathogen by the host plant & leads to the activation of a cascade of biochemical reactions in the attacked plant cells

  
• Gene-for-gene interaction


  • R gene recognizes a single corresponding pathogen protein (Avirulence gene)
  • If pathogen is recognized: Resistant Plant - Avirulent pathogen
  • If pathogen is not recognized: Susceptible plant - Virulent pathogen
• Plantibodies


  Antibodies that are encoded by animal genes but produced in transgenic plants
• Plantibodies


  • Plantibodies against virus coat proteins; when engineered in plants, plants become resistance to the virus that where the plantibody was derived

  
• Defense through Genetic Engineering

  Using plant-derived genes (R genes) or pathogen-derived genes to generate resistance in susceptible plants