Final Exam

• Plant pathogens are microorganisms that can attack plants and cause disease
• Bacteria cause:

  • leaf blight
  • leaf spots
  • canker
• Fungi cause:

  • powdery mildew
  • anthracnose
  • alternaria blight
• Viruses cause:

  • tobacco mosaic virus
  • tomato spotted wilt
• Viroids cause:

  • citrus excortis
  • avocado sunblotch
• The disease life cycle includes:

  • inoculation
  • pathogen comes in contact with host
  • pre-penetration
  • attachment to host
  • spore germination
  • appressorium formation
  • growth of nematodes
  • penetration
  • using natural openings or wounds
  • infection
  • intimate contact
  • colonisation
  • intercellular or intracellular
  • growth and reproduction
  • growth and spread within host until death or limit is reached
• Symbiosis:

  Close association of two different species living together, where at least one party benefits
• Parasitism:

  One organism benefits at the expense of the host
• Commensalism

  One partner benefits, while the other is neither helped nor harmed
• Mutualism

  Both parties benefit from each other
• Functions of the leghaemoglobin:

  • oxygen supply to the bacteroid
  • maintenance of low free oxygen concentrations to prevent nitrogenase damage
• Hemiparasites are green plants that can perform photosynthesis but depend on their host for supply of water and nutrients
• Holoparasites are totally dependent on their hosts for all water and nutrient requirements
• Hemiparasites:

  • supply themselves with carbohydrates
  • import carbon via transpiration
  • get most of their nutrients from haustorial attachments
  • high rates of transpiration
  • low shoot water potential
  • may live independent of host for some period
  • found in light areas
• Holoparasites:

  • dependent on host for all water and nutrients
  • no chlorophyll
  • will die after germination if all endosperm nutrients are exhausted and a haustorium has not been established
  • root parasites
  • found in dark places
  • all or most of the vegetative body is hidden within the host, with only flowers surfacing
• Mention two similarities between the carnivorous plant leaf as an all-in-one organ and the animal digestive tract:

  1. Highly acidic digestive fluids
  2. Pepsin-like enzymes to break down animal proteins
• Mention the advantages that carnivory offers plants in habitats where soil nutrient supply is scarce:

  Carnivory provides extra source of NPK nutrients from prey, which can be allocated to reproduction. Nitrogen can be used to produce additional RuBisCO to increase photosynthesis, and carbon can be used as an energy source and bypass photosynthesis
• Marginal benefit:


  increased rate of photosynthesis per unit of photosynthate invested in structures
• Marginal cost:


  unit photosynthate required for the production of additional carnivorous structures
• Facilitation:

  modification of the environment to benefit neighbouring plants
• Competition:


  utilisation of a large share of available resources to the detriment of the neighbours
• Resource competition:

  utilisation of the same pool of growth-limiting resource
• Interference competition:

  allelopathy

  production of chemicals that negatively affect neighbours
• Explain the adaptive strategies employed by plants to maximise resource acquisition

  quick growth for increased sunlight and shading of neighbours

  differing root depth

  promote leaf senescence for nutrients for new tissues

  high root length density
• Direct defence:

  accumulation of toxic compounds to reduce feeding and destroy pathogens
• Indirect defence:

  release of volatiles that attract predators of herbivores
• What is environmental sustainability?

  The ability to maintain natural resources and ecological balance for present and future generations
• Explain the role of plant beneficial microbes in promoting environmental sustainability

  Issue:

  • Haber-Bosch process causes nitrogen deposition
  • water acidification
  • eutrophication
  • decreased decomposition and altered nutrient cycling

  Cyanobacteria as fertilisers:

  • break down pollutants -> help in bioremediation
  • boost soil fertility
  • improved agro-ecosystem health and food security
  • increased crop productivity and quality
  • fix nitrogen
  • release oxygen as byproduct