Apprenticeship Level 3 Production

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ApprenticeshipLevel 3 - Production

• Bacterial And Viral Diseases

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Bacteria

• Prokaryotic microscopic organisms
• Free living single cells, or
• Filamentous colonies
• Reproduce via binary fission
• 2 daughter cells are identical to mother cell
• Dont usually produce resistant resting spores
• Need host or growth medium to survive
• For rapid spread, plant infecting bacteria
  usually require
• Warmth
• Moist conditions

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Bacterial Diseases on Plants

• Less common than fungal or viral diseases
• They can be either
• parasites, saprophytes, or autotrophs
• Symptoms include
• Cankers, Wilts, Shoot Blights, Leaf Spots,Scabs,
  Soft Rots, Galls
• Generally, cannot invade healthy tissue need
  wound or opening to infect.
• Control methods usually cultural in nature (dont
  use antibiotics on large scale)

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Prunus leaf spot
Xanthomonas prunii
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Bacterial wilt of cucurbits
Erwinia tracheiphila
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Crown gall
Agrobacterium radiobacter var. tumefaciens
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Controlling Bacteria

• Chemicals not too effective
• Biological agents
• Only one available - Agrobacterium radibacter
  var. radiobacter
• Used to outcompete the pathogenic strain - A.
  radibacter var. tumefaciens which causes crown
  gall
• Also, strain K 84 (Dygall) is registered as a
  disease protective dip, since it will antagonize
  the pathogenic strain

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Controlling Bacteria

• Cultural controls satisfactory
• Since they rely on moisture (for dispersal
  reproduction)
• Reduce free water by
• Avoid splashing or overhead irrigation
• Provide good air circulation (drying)
• Provide good drainage
• Use disease-free planting stock
• Minimise handling/wounding
• Minimise damage by plant-feeding pests
• Disinfect cutting tools propagation areas

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Controlling Bacteria

• Cultural controls (continued)
• Wash hands, clothing tools (sanitation)
• Pasteurize growth media, if possible
• Manage cropping dont plant susceptible crops in
  contaminated soils
• Prune destroy infected tissues
• Remove destroy infected plants galls
• Clean growing area after cropping before
  planting again

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Bacterial Canker

• Infection caused by bacteria
• Pseudomonas syringae
• Also called bacterial blast or gummosis
• Hosts infected include the Prunus family,
  Cherry, Plums, Pear, Tomato, Sour cherry, Prunes,
  Almonds
• Very troublesome in the Pacific Northwest but
  also been reported in England, Continental
  Europe, Australia, and New Zealand

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Symptoms

• Brown spots develop on leaves in the spring,
  sometimes surrounded by a yellow halo.
• The spotted areas fall out giving a distinctive
  'shot hole' appearance.
• Cankers enlarge rapidly on the stems in spring.
  Stems with cankers exude gum.
• Leaves on cankered stems are yellow, then rapidly
  shrivel and die.

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Disease Development

• Infections occur through leaf scars and wounds.
  These give rise to small cankers in which the
  bacteria survive the winter.
• Rain or water splash, and pruning tools spread
  the bacterium.
• Bacteria overwinter in active cankers, in
  infected buds, and on the surface of infected and
  healthy trees and weeds.
• The bacterium reproduces best between 21ºC and
  25ºC.
• The disease seems to be more severe after cold
  winters and prolonged spring rains.

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Disease Cycle

• The bacteria can survive from one season to the
  next in bark tissue at canker margins, in
  apparently healthy buds and systemically in the
  vascular system.
• Bacteria multiply within these overwintering
  sites in the spring and are disseminated by rain
  to blossoms and to young leaves.
• After leaves abscise in autumn, the bacteria may
  enter the tree through fresh leaf scars.
• Outbreaks of bacterial canker are often
  associated with prolonged periods of cold,
  frosty, wet weather late in the spring or with
  severe storms that injure the emerging blossom
  and leaf tissues.

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Cultural Controls

• Pruning should be carried out in the summer
  during dry weather, as infection of the branches
  occurs in autumn and winter.
• Cultivar choice some resistance evident in
  certain host cultivars.
• Prevent frost damage excessive wet periods
  (reduce susceptibility)
• Prevention (clean seed, soil, stock, etc.)

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Viruses

• Viruses are "submicroscopic" entities that infect
  individual host plant cells.
• Viruses are obligate parasites They can only
  replicate themselves within a host's cell.
• In the virus infected plant, production of
  chlorophyll may cease (chlorosis, necrosis)
• Cells may either grow and divide rapidly or may
  grow very slowly and be unable to divide

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Viral Diseases

• gt 400 viruses infect plants few are economically
  important pathogens
• The infection remains forever
• Viruses are transmitted from plant to plant by
  living factors insects, mites, fungi and
  nematodes
• Or non-living factors rubbing, abrasion or other
  mechanical means (including grafting or other
  forms of vegetative propagation)
• Occasionally transmitted in seed.

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Virus Disease Symptoms

• The symptoms of most virus diseases can be put
  into four categories
• Lack of chlorophyll formation in normally green
  organs.
• Stunting or other growth inhibition
• Distortions
• Necrotic areas or lesions

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Cucumber Mosaic Virus (CMV)

• Vectored by aphids
• Affects variety of vegetables (tomato, pepper,
  cucumber, melons, squash, spinach, celery,
  beets), ornamentals (chrysanthemums, petunia) and
  weeds
• General symptoms
• Slight yellowing/mottling of older leaves
• Expanding leaves twist and curl
• Stunted plants with less fruit
• Control options
• removal, sanitation, control weeds aphids

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Tomato Spotted Wilt Virus (TSWV)

• Vectored by thrips infected plant material
• Affects ornamentals, weeds, pepper, lettuce
  solonaceous (tomato) family
• General symptoms
• Inward leaf cupping with off-colour foliage
• Wilting/yellowing of plant
• On fruit while to yellow concentric rings
• Control options
• Eliminate source (weeds, thrips, sanitation)

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Principles of Disease Control

• Host susceptibility
• Pathogen virulence
• Pathogen-favourable environmental conditions

EQUALS WHAT? A susceptible ______ meets a
virulent ___________ in a favourable_________!
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Disease Triangle