Climate Change: Plant Disease Management Stella Melugin

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Climate Change Plant Disease Management

• Stella Melugin Coakley
• Oregon State University

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Plant Pathogens in aChanging World
Harald Scherm University of Georgia, Athens
Stella M. Coakley Oregon State University,
Corvallis
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2003 Australasian Plant Pathology 32, 157-165
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Elements of Global Change

• Climate change--- temperature and moisture
• Atmospheric trace gases (CO2, O3, CH4, etc.)
• Land use/ land cover changes
• Invasive species
• Biodiversity loss

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Examples from history

• Asian chestnut blight fungus
• Eliminated American chestnut and with it, several
  phytophagous insects
• In Australia, Phytophthora cinnamoni
• Converted large areas of Eucalyptus forest to
  monocot-dominated open savanna
• Eliminated potential nest sites and food for many
  animals

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How may climate change impact disease management?

• Pathogens are very dependent on environment for
  disease development
• Pathogens often exist at low levels but erupt
  into epidemics rapidly under favorable conditions
  
• Prevention is preferable to management

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Focus on climate warming with increased
precipitation

• Influence pathogen
• Increased overwintering may gt severity
• e.g. Mediterranean oak decline, Dutch elm
  disease, wheat stripe rust
• Influence host
• Rapid growth, increased canopy humidity
• Influence vectors of pathogens

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Mechanisms of impact

• More rapid pathogen development
• Fungus on groundnut
• More rapid vector development
• Vector (Toxoptera sp.) of Citrus tristeza virus
• Increased overwintering of pathogen/vector
• Barley yellow dwarf, potato leafroll virus,
  yellows virus, Oak root rot

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Mechanisms of impact (cont)

• Increased pathogen transmission
• Fusarium moniliforme on Capri fig
• Fungus on oilseed rape
• Increased host susceptibility
• Phytophthora on soybean
• Potato virus Y on potato
• Foliar rust on oats (resistance inactive)

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Evidence of aphid vectors
responding toclimate warming

• Aphids in Britain
• Suction trap network since 1964
• First spring catch related to winter T
• Advance of spring flight phenology by 3 to 6 days
  in past 25 years (Fleming Tatchell 1995)
• During same period, T increased by 0.4oC

Harrington (2002)
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Most severe and least predictable disease
outbreaks

• When geographic ranges are altered by climate
  change
• Allows formerly disjunctive species and
  populations to converge
• Introduction of pathogen that spreads to new
  hosts (sudden oak death, Dutch Elm disease)
• Introduction of new plant which encounters
  pathogens native to area (wheat to Brazil, coffee
  to Asia)

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Limited Prospects for Finding Climate Change
Fingerprints for Plant Diseases

• Few standardized long-term data sets
• Overwhelming influence of management unmanaged
  systems rarely monitored
• Few disease data sets that focus on phenology
  rather than disease intensity
• Overwhelming influence of localized variables
  (e.g. moisture) that may vary more under climate
  change

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Challenges for Modeling Effects of Climate Change
on Plant Diseases

• Uncertainty in climate change projections IPCC
  1996 ?T 1.0 to 3.5oC by 2100
• IPCC 2001 ?T 1.4 to 5.8oC
• Nonlinear response mean temperature insufficient
  to make accurate predictions
• Evolution pathogens likely to adapt genetically

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Where should attention be focused?

• On introduction of new material
• History of host and pathogen populations at site
  of origin
• Prevention of pathogen introduction may not be
  possible but early intervention may prevent more
  extensive losses

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Invasive Pests

• Are both cause and consequence of global change
• In US, cost 137 billion per year 20 due to
  exotic plant pathogens (Pimentel et al. 2000)
• By 1991, 239 exotic plant pathogen species in US
• Rate of introduction
• 1940-70 lt5 per decade (NRC, 2002)
• 1990s considerably higher

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Exotic Plant Pathogens First Detected in the US
in the1990s

• Field crops
• Sorghum ergot
• Soybean rust (Hawaii)
• Karnal bunt
• Forests
• Eurasian leaf rust of poplar
• Leaf spot of hybrid poplar
• Sudden oak death
• Needle blight of spruce
• Ornamentals
• Powdery mildew of Sedum
• Powdery mildew of Nandina
• Powdery mildew /f poinsettia

• Fruits and vegetables
• Cucurbit aphid-borne yellows virus
• Cucurbit yellow stunting disorder virus
• Powdery mildew of tomato
• Phytophthora rot of cabbage
• Plum pox virus
• Tomato yellow leaf curl
• Citrus canker

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1) Can Pest Invasions be Predicted?

• Based on life-history attributes of pest
• Based on invasibility of environment

National Research Council (2002)
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2) Macroevolution Following Introduction of
Exotic Pathogens
Hybridization between related allopatric species
? new pathogen species

• Hybrids with combined host range of both parents
  Melampsora ? columbiana on poplar Newcombe et
  al. (2000) Mycol. Res. 104
• Hybrids with new host specificity Phytophthora
  sp. on alder, a hybrid between P. cambivora and a
  P. fragariae-like species Brasier et al. (1999)
  PNAS 96

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Conclusions

• Challenge will be rapid identification and
  management of new diseases
• Tools for management will change under changing
  global conditions, e.g. water quality issues may
  preclude use of certain chemical controls
  phase-out of methyl bromide
• Important challenges remain in developing
  meaningful models of disease intensity and crop
  losses under climate change

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Conclusions (cont)

• Important lessons can be learned from studying
  patterns of pathogen invasions and pathogen
  evolution in response to global change
• Where hosts go, pathogens will follow
• Best management will be from exclusion or early
  detection and elimination where possible