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Environment-Pathogen Interaction in Plant Diseases

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Rajat Sharma

This document summarizes a seminar presentation on the interaction between the environment and plant pathogens in plant diseases. It discusses how climate change impacts the three elements of the disease triangle: the host, pathogen, and environment. It describes how increased carbon dioxide and temperatures can influence pathogen growth and disease development. Specifically, it provides examples of how higher temperatures and carbon dioxide levels can increase the severity of certain diseases in crops like wheat, citrus, and soybean, while decreasing other diseases. The document also reviews historical developments in the field of plant disease epidemiology.

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MASTER’S SEMINAR “Environment-Pathogen Interaction In Plant Diseases” Rajat Sharma H-2017-67-M M.Sc. 2nd Year on
INTRODUCTION • Climate change is a major environmental challenge worldwide. Green house gases (GHG) viz., water vapour (H2O), carbon dioxide (CO2), Methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs) and Ozone (O3) in the atmosphere trap reflected radiation to warm the earth surface (Mahato, 2014). • Human activities are widely involved in increasing global climate changes that directly influences the ecology (Pachauri and Reisinger, 2007 and Ahanger et al., 2013). • According to Inter-govenrmental Panel on Climate Change (IPCC, 2007); the planet earth is experiencing a climate change and atmospheric CO2 is a major GHG, which increased by nearly 30% and temperature by 0.3- 0.6°C.
• This global climate changes by various factors (Pachauri and Reisinger, 2007 and Pachauri et al., 2014) and change or influence all the 3 major elements of disease triangle, viz., host, pathogen and environment (Legreve and Duveiller, 2010). • Crop growth and production can be significantly affected due to high atmospheric CO2 concentration, temperature, changes in precipitation patterns and frequency of extreme weather phenomena and diseases presence will altered under these condition (Rosenzweig and Tubiello, 2007, Ghini et al., 2008 and Chakraborty, 2011). • When the host present pathogens with short life cycles, reproduction rates is high and dispersion mechanisms respond quickly and adapt faster to climate change (Coakley et al., 1999).
• Climate change would affect plant diseases together with anthropogenic processes such as air, water and soil pollution, long-distance introduction of exotic species and urbanization (Regniere, 2012). • These factors contribute to the spread of diseases viz. sudden oak death (Prospero et al., 2009). Elevated temperature and CO2 concentration have impact on plant-disease interaction (Lopez et al., 2012) and posing a higher threat perception of late blight (Phytophthora infestans) of potato and blast (Magnaporthe grisea) and sheath blight (Rhizoctonia solani) of rice (Kobayashi et al., 2006).
Environment-Pathogen Interaction in Plant Diseases
EPIDEMIC Change in disease intensity in a host population over time and space. EPIPHYTOTIC Unger (1833), Whetzel (1920's) Being a plant disease that tends to recur sporadically and to affect large numbers of susceptible plants. EPIDEMIOLOGY Science of disease in populations. Vanderplank(1963) • Study of the spread of diseases, in space and time, with the objective to trace factors that are responsible for, or contribute to, epidemic occurrence.
HISTORY (ANCIENT TO MODERN TIMES) Hippocrates (~400 BC) : First use of "epidemic", widespread disease (human disease. Theophrastus (~340 BC) : Plant diseases in fields, Environmental influences Pliny (~50 AD) : Plant diseases; soil; climate. Duhamel de Monceau : Disease progress curves. (1728 AD) Late 19th Century and forward… Kuhn (1858) - 1st textbook of plant pathology. Ward (1901): Book "Diseases in Plants" emphasized ecology (populations) of disease. Jones (1913) - Role of the environment. Gaumann (1946): "Principles of Plant Infection” -Disease spread, - Conditions leading to an epidemic, -'Infection Chain' (= disease cycle),-compare with medicine (disease of humans).
Large(1952, andothers) -Disease progress curves -Crop losses -Disease assessment (measurement) Horsfall & Dimond (1960)- "Plant Pathology, Volume 3" -Populations -Inoculum density:disease relations -Spore dispersal -Analysis (mathematics) -Forecasting, prediction -Traditional definition ---> Modern definition Gregory(1963, 1973) "The Microbiology of theAtmosphere" -spore dispersal, disease spread Aerobiology Vanderplank (1963) (usedto be van der Plank) "Plant Diseases: Epidemics and Control" -Populations -Rates (dynamic processes) -Analysis, mathematics -Models, theory -Link epidemiology and control -Established the science of plant disease epidemiology Other pioneers: Zadoks (1960-1995), TheNetherlands Kranz (1968-1995),Germany Waggoner (1960-mid --1980s),USA S. Nagaranjan1983-India
ELEMENTS OF AN EPIDEMIC 1) Host 2) Pathogen 3) Environment Interactions of the 3 main components are described by the disease triangle. The Disease Triangle Disease development is also affected by 4. Time 5. Humans Disease Tetrahedron Interactions of the 5 components are described by the disease pyramid.
Environment-Pathogen Interaction in Plant Diseases
Environment-Pathogen Interaction in Plant Diseases
HOST FACTORS All plants can be considered hosts. o Degree of genetic uniformity. o Age – affects disease development depending on plant-pathogen interaction. There are different levels of susceptibility, which include: o Immune - cannot be infected. o Susceptible - can be infected. o Resistant - may or may not be infected.
ENVIRONMENTAL FACTORS i. Moisture -Rain, dew, high humidity. -Dominant factor in diseases caused by oomycetes, bacteria & nematodes. ii.Temperature - Affects disease cycles of pathogens Diseasedevelopment is also affected by  Time factors • Season of the year • Duration & frequency of favorable temp. & rains • Appearance of vectors, etc.  Humans How HumansAffect Development of Epidemics • Site Selection & Preparation. • Selection of Propagative Material. • Introduction of Exotic Pathogens. • Cultural Practices. • Disease control measures.
CLIMATE CHANGE & MICROBIAL INTERACTIONS i. Nitrogen deposition level, CO2 concentration and temperature are important factors affecting soil microbial communities (Garret et al., 2006). ii. Increased CO2 levels in the atmosphere have major consequences on carbon cycling and the functioning of various ecosystems. iii. Short-term and long-term changes in the abiotic conditions not only affect plant growth and productivity but also the populations of microorganisms living on plant surfaces. iv. Any change in phyllosphere microflora, affects plant growth and plants’ ability to withstand aggressive attack of pathogens.
EFFECT OF TEMPERATURE Certain minimum temperature is required by both plants and pathogens to grow. Temperature affects the chain of events in disease cycles such as survival, dispersal, penetration, development and also reproduction rate for many pathogens. Generally high moisture and temperature favours and initiate disease development, as well as germination and proliferation of fungal spores of diverse pathogens (Agrios, 2005).
EFFECT OF TEMPERATURE • Plants, as well as pathogens, require certain minimum temperatures to growandcarryout their activities. • At higher temperatures, pathogens become active and, they can infect plants andcausedisease. • Cankerdiseasesof perennial plants causedby:  fungi Nectria, Leucostoma (Cytospora), the oomycete Phytophthora  bybacteriasuchas Pseudomonas, • Infections beginanddevelop primarily in earlyspring or in thefall. • During these periods the temperatures are high enough for these fungi to growwell but aretoo low to allow optimum hostdevelopment.
TEMPERATURE AFFECTS: 1. The number of spores formed in aunit plant area. 2. The number of spores released in a given time period.
• Due to changes in temperature and precipitation, climate change may alter the growth stage, development rate, pathogenicity of infectious agents, and the physiology and resistance of the host plant (Charkraborty and Datta, 2003). • Sunlight affects pathogens due to the accumulation of phytoalexins or protective pigments in host tissue. • Host plants such as wheat and oats become more susceptible to rust diseases with increased temperature; but some forage species become more resistant to fungi with increased temperature (Coakley et al., 1999).
• With increasing temperature spore germination of rust fungus Puccinia substriata increases (Tapsoba and Wilson, 1997). • In southern Germany, a northward shift of Cercospora beticola, leaf spot of sugar beeet was due to increasing annual mean temperature by 0.8-1°C (Richerzhagen et al., 2011). • Altered temperatures favour over-wintering of sexual propagules which increased the evolutionary potential of a population (Pfender and Vollmer (1999). • Conidia of powdery mildew have the ability to germinate even at 0% relative humidity (RH) (Yarwood, 1978). • Conidia of Erisiphe cichoracearum germinate at temperature from 7 to 32°C with a RH of 60 to 80% (Khan and Khan, 1992); and spores of Erysiphe necator germinate at temperatures from 6 to 23°C with a RH from 33 to 90 % (Bendek et al., 2007).
• Phytophthora infestans, late blight of potato and tomato, infects and reproduces most successfully at high moisture when temperatures are between 7.2°C and 26.8°C. • Infection of Eucalyptus sp. by Phytophthora cinnamomi due to increased soil temperature of 12-30°C (Podger et al., 1990). • Even the incidence of virus and other vector borne diseases also alter. Mild and warmer winters make aphids easy to survive thus spreading Barley yellow dwarf virus (BYDV) and also increase viruses of potato and sugar beet (Thomas, 1989; Mackerron et al., 1993).
RISK ANALYSIS STUDIES ON THE EFFECTS OF CLIMATE CHANGE STUDY RESULT REFERENCE • In the UK, the effects of climate change on Phoma (Leptosphaeria maculans) were assessed. Epidemics will not only increase in severity but also spread northwards by the 2020s. Evans et al., 2007 • Future scenarios of downy mildew on grapevine (Plasmopara viticola) were simulated from the results of two climate change models. The results suggested that the incidence of disease would increase and the production of grapes in northwestern Italy would decrease. Predicted an increase of the disease pressure in each decade to consequence of more favorable temperature conditions. Salinari et al., 2006 • A model to assess the severity of Phytophthora infestans under climate change was developed A marked shift of the disease in the infestation pressure to higher altitude Kocmankova et al., 2007
STUDY RESULT REFERENCE The effects of elevated levels of CO2 and temperature on the incidence of four major chili pepper diseases  (Anthracnose (Colletotrichum acutatum)  Phytophthora blight (Phytophthora capsici)) and • two bacterial diseases (bacterial wilt (Ralstonia solanacearum) and bacterial spot (Xanthomonas campestris pv. vesicatoria)) were determined. Elevated CO2 and temperature significantly increased the incidence of two bacterial diseases. Anthracnose decreased and Phytophthora blight slightly increased. Shin and Yun, 2010
A summary of the influence of elevated Temperature on some Host and Pathogen Interaction CROP/HOST DISEASE/PATHOGEN CLIMATE CHANGE CHANGE IN DISEASE SEVERITY AUTHOR/REFERENCE Wheat Stripe rust – Puccinia striiformis Elevated average annual temperature Decrease Yang et al., 1998 Wheat Dwarf bunt- Tilletia controversa Elevated temperatures Increase Boland et al., 2005 Wheat Wheat Stripe rust – Puccinias triiformis Higher Temperature Increase Milus et al., 2006 Citrus Anthracnose- Colletotrichum acutatum Elevated Temperatures Increase Jesus Junior et. al., 2007 Potato Late blight – Phytophthora infestans Elevated temperatures causing earlier seasons Increase Hannukkala et al., 2007 Papaya Asperisporium caricae Elevated temperatures and lower relative humidity Decrease Jesus Junior et. al., 2007 Pineapple Fusarium subglutinans Elevated temperatures Decrease Matos et al., 2000 Coffee Meloidogyne incognita Elevated temperatures Increase Ghini et al., 2008
EFFECT OF CO2 a. Increased size of plant organs, leaf area, leaf thickness, more numbers of leaves, higher total leaf area/plant, stems and branches with greater diameter are resulted from increased CO2 levels (Bowes, 1993 and Pritchard et al., 1999). b. Dense canopy favours the incidence of rust, powdery mildew, Alternaria blight, Stemphylium blight and anthacnose diseases. c. Higher CO2 concentrations induce greater fungal spore production. Increased CO2 also enhances photosynthesis, increased water use efficiency and reduced damage from ozone (von Tiedmann and Firsching, 2000); and leaf area, plant height and crop yield are increased at higher doses of CO2 (Eastburn et al., 2011). d. The physiological changes on the host plant due to increased CO2 can conversely result in increase host resistance to pathogens (Coakley et al., 1999).
EFFECT OF C02 i. Under elevated CO2 conditions, potential of dual mechanism i.e., reduced stomata opening and altered leaf chemistry results in reduced disease incidence and severity in many plant pathosystems where the pathogen targets the stomata (Mcelrone et al., 2005). ii. In soybean, elevated concentration of CO2 and O3 altered the expression of 3 soybean diseases, downy mildew (Perenospora manshurica), brown spots (Septoria glycines) and sudden death syndrome (Fusarium virguliforme) (Eastburn et al., 2010). iii. Elevated CO2 also leads to production of papillae and accumulation of silicon by barley plants at the site of appressorial penetration of Erysiphe graminis and changed leaf chemistry that decrease susceptibility to the powdery mildew pathogen (Hibberd et al., 1996).
EFFECT OF INCREASED CO2 CONCENTRATIONS ON PATHOGENS STUDY RESULT REFERENCE • The effect of elevated concentrations of CO2 on the infection of barley by Erysiphe graminis was determined. The percentage of conidia that progressed to produce colonies was lower in plants grown in 700 than in 350ppm CO2. Hibberd et al. (1996) • Interactive effects of elevated CO2 and O3 levels on wheat leaves infected with leaf rust fungus Puccinia triticina were described. Elevated CO2 increased the photosynthetic rates of the diseased plants by 20 and 42% at the ambient and elevated ozone concentrations, respectively. Tiedemann and Firstching (2000). • The effects of elevated CO2 concentrations on the development of Phytophthora parasitica (root rot) in tomato were evaluated. The extra CO2 completely counterbalanced the negative effect of the pathogenic infection on overall plant productivity. Jwa and Walling (2001). • Pyricularia oryzae Cavara and Rhizoctonia solani Kühn were evaluated. Rice plants grown in an elevated CO2 concentration were more susceptible to leaf blast than those in ambient CO2. Kobayashi et al. (2006).
STUDY RESULT REFERENCE • The effects of carbon dioxide (CO2) and ozone (O3) on three soybean diseases (downy mildew, Septoria and sudden death syndrome) were determined in the field. Changes in atmospheric composition altered disease expression. Elevated CO2 reduced downy mildew disease severity. But increased brown spot severity and without effect in sudden death syndrome. Eastburn et al. (2010). • The response of tobacco to potato virus Y was evaluated. The titre of viral coat-protein was markedly reduced in leaves under these conditions at both nitrogen levels. The accumulation of phenylpropanoids, may result in an earlier confinement of the virus at high CO2. Matros et al. (2006). • The germination rates of conidia of C. gloeosporioides were determined. spore germination was reduced and extended incubation period was at 700 ppm, and Anthracnose severity was reduced. Chakraborty et al. (2002).
EFFECT OF MOISTURE • It influences the initiation and development of infectious plant diseasesin many interrelatedways. Moisture is indispensablefor:  The germination of fungalspores  Penetration of the host by the germ tube  Activation of bacterial, fungal, and nematode pathogens before they caninfect theplant.  The spread of pathogens on the same plant and from one plant to another • Moisture increases the succulence of host plants and thus their susceptibility to certain pathogens, which affects the extent and severity ofdisease.
EFFECT OF MOISTURE With increased temperature extreme rainfall events and higher atmospheric water vapour concentrations take place. i. These encourage the crops to produce healthier and larger canopies that retain moisture as leaf wetness and RH for longer periods and results in condition conducive for pathogens and diseases such as late blights and vegetable root diseases including powdery mildews (Coakley et al., 1999). ii. High moisture favours foliar diseases and some soil borne pathogens such Phytophthora, Pythium, R. solani and Sclerotium rolfsii. iii. Drought stress affect the incidence and severity of viruses such as Maize dwarf mosaic virus (MDMV) and Beet yellows virus (BYV) (Olsen et al., 1990 and Clover et al., 1999).
EFFECT OF WIND Wind influences infectious plantdiseases: • primarily by increasing the spread of plant pathogens and the number of wounds on host plants. • to a smaller extent, by accelerating the drying of wet surfaces of plants. • fungi, bacteria, and viruses that are spread either directly by the wind or indirectly by insect vectors that can themselves be carried over long distances by thewind. • wind-blown rain helps release spores and bacteria from infected tissue and then carries and deposits them on wet surfaces of plants, which, if susceptible, can be infected.
EFFECT OF LIGHT • The intensity and the duration of light may either increase or decrease the susceptibility of plants to infection. • Low light produces etiolated plants, which increases the susceptibility of plants to non obligate parasites. Tomato plants to Botrytis or to Fusarium. • Reduced light intensity generally increases the susceptibility of plants tovirus infections. • Low light intensities following inoculation tend to mask the symptoms of somediseases.
EFFECT OF SOIL pH & SOIL STRUCTURE • The pH of the soil is important in the occurrence and severity of plant diseases caused by certain soil borne pathogens.  Clubroot of crucifers (Plasmodiophorabrassicae) severe -pH 5.7 drops between pH5.7 -6.2 and completely checked -pH7.8.  Cotton root rot fungus (Phymatotrichopsis omnivora) exists only in soils contain relatively high concentrations of calciumcarbonate.
EFFECT OF HOST-PLANT NUTRITION Nutrition affects the rate of growth and the state of readiness of plants. • Nitrogen: abundance results in the production of young, succulent growth, a prolonged vegetative period, and delayed maturity of the plant, make the plant more susceptible topathogens. • Phosphorus: increase resistance by improving the balance of nutrients in the plant or by accelerating the maturity of the crop and to escape infection by pathogens that prefer younger tissues.
Potassium : • Have a direct effect on pathogen establishment and development in thehost. • And an indirect effect on infection by promoting wound healing. • Potassium also increases resistance to frost injury. Calcium: Effects the composition of cell walls and their resistance to penetrationby pathogens. Various micronutrients (Fe, Cu,Mn,Mg,Si) showed decreased infection when levels of nutrients increased.
EFFECTOF HERBICIDES AND AIR POLLUTANTS: i. The direct effects may include stimulation or retardation of the growth of the pathogen or in the susceptibility of the host. ii. Indirect effects include effect on activity of soil microflora, elimination or selection of the pathogen by certain alternate hosts, or alteration of the microclimate of the crop plant canopy. iii. ozone, can affect a pathogen and sometimes the disease it causes. The rate of infection is reduced if the exposure to ozone is early but is increased if exposure occurs late.
EFFECT OF CLIMATE CHANGE ON VECTOR- BORNE DISEASES i. The risk of vector-borne disease at the local and regional level is limited by the climatic requirements of disease vectors (Malmstrom et al., 2011). ii. Both host plant and insect-vector populations are affected by climate change and spread the plant viruses (Jones, 2009). iii. Climate change influences the primary infection of the host, the spread of the infection within the host and/or the horizontal transmission of the virus to new hosts by the vector along with phenology and physiology of the host thereby affect its virus susceptibility and virus ability to infect. iv. Climate change has various effects on vectors like modification of vector phenology, vector’s over-wintering, density, migration and its stability.
CASE STUDY-I
Environment-Pathogen Interaction in Plant Diseases
Environment-Pathogen Interaction in Plant Diseases
CASE STUDY-II
1. POWDERY MILDEW
2. LEAF RUST
3. STEM RUST
Environment-Pathogen Interaction in Plant Diseases
Environment-Pathogen Interaction in Plant Diseases
CASE STUDY-III
Environment-Pathogen Interaction in Plant Diseases
Environment-Pathogen Interaction in Plant Diseases
RESEARCH NEEDS 1. The effectiveness of disease management strategies. Assessing current management strategies and proposing alternatives will prepare us for the challenge of climate change. This will allow our mitigation measures to be more efficient and adaptable to change. 2. The risk of disease must be analyzed to determine the geographical distribution and modification of diseases due to climate change. 3. Plant diseases and crops must be modeled. Mathematical models can be used to perform quantitative analysis of the phytosanitary problems. They provide a very powerful tool to understand and represent interactions among weather, crop and disease variables (Allman and Rhodes, 2004). 4. Mathematical models can help to assess the probability of introduction, reproduction and dispersion of diseases, and the magnitude of their effects on crops yield and quality in current scenarios and under climate change. 5. Factors limiting the survival of pathogens should be characterized (e.g., temperature, humidity, CO2, O3 and radiation).
CONCLUSION • Climate change is an important phenomenon that affects agricultural production. By anticipating the future, we can prepare ourselves for problems caused by climate change, especially those related to agricultural activities. • Global warming may modify areas affected by pests and diseases, studies must be performed to assess pest and disease stages under the effects of climate change, determine the magnitude of disease and identify measures to minimize the risk of infection. • Exposure to altered atmospheric conditions can modify fungal disease expression. Studies had shown that exposure at elevated CO2 increases disease incidence or severity in some cases but in other cases decreased.
• These highlight how the host–pathogen interactions make it difficult to devise general principles that govern changes across fungal pathosystems. So increase or decrease disease will be in function of the host and pathogen. • Climate change may affect the actual, spatial and temporal distribution of diseases; however, the magnitude of these effects remains unclear. • Disease risk analysis based on host-pathogen interactions should be performed, and research on host response and adaptation should be conducted to understand how an imminent change in the climate could affect plant diseases.
Environment-Pathogen Interaction in Plant Diseases

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Environment-Pathogen Interaction in Plant Diseases

  • 1. MASTER’S SEMINAR “Environment-Pathogen Interaction In Plant Diseases” Rajat Sharma H-2017-67-M M.Sc. 2nd Year on
  • 2. INTRODUCTION • Climate change is a major environmental challenge worldwide. Green house gases (GHG) viz., water vapour (H2O), carbon dioxide (CO2), Methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs) and Ozone (O3) in the atmosphere trap reflected radiation to warm the earth surface (Mahato, 2014). • Human activities are widely involved in increasing global climate changes that directly influences the ecology (Pachauri and Reisinger, 2007 and Ahanger et al., 2013). • According to Inter-govenrmental Panel on Climate Change (IPCC, 2007); the planet earth is experiencing a climate change and atmospheric CO2 is a major GHG, which increased by nearly 30% and temperature by 0.3- 0.6°C.
  • 3. • This global climate changes by various factors (Pachauri and Reisinger, 2007 and Pachauri et al., 2014) and change or influence all the 3 major elements of disease triangle, viz., host, pathogen and environment (Legreve and Duveiller, 2010). • Crop growth and production can be significantly affected due to high atmospheric CO2 concentration, temperature, changes in precipitation patterns and frequency of extreme weather phenomena and diseases presence will altered under these condition (Rosenzweig and Tubiello, 2007, Ghini et al., 2008 and Chakraborty, 2011). • When the host present pathogens with short life cycles, reproduction rates is high and dispersion mechanisms respond quickly and adapt faster to climate change (Coakley et al., 1999).
  • 4. • Climate change would affect plant diseases together with anthropogenic processes such as air, water and soil pollution, long-distance introduction of exotic species and urbanization (Regniere, 2012). • These factors contribute to the spread of diseases viz. sudden oak death (Prospero et al., 2009). Elevated temperature and CO2 concentration have impact on plant-disease interaction (Lopez et al., 2012) and posing a higher threat perception of late blight (Phytophthora infestans) of potato and blast (Magnaporthe grisea) and sheath blight (Rhizoctonia solani) of rice (Kobayashi et al., 2006).
  • 6. EPIDEMIC Change in disease intensity in a host population over time and space. EPIPHYTOTIC Unger (1833), Whetzel (1920's) Being a plant disease that tends to recur sporadically and to affect large numbers of susceptible plants. EPIDEMIOLOGY Science of disease in populations. Vanderplank(1963) • Study of the spread of diseases, in space and time, with the objective to trace factors that are responsible for, or contribute to, epidemic occurrence.
  • 7. HISTORY (ANCIENT TO MODERN TIMES) Hippocrates (~400 BC) : First use of "epidemic", widespread disease (human disease. Theophrastus (~340 BC) : Plant diseases in fields, Environmental influences Pliny (~50 AD) : Plant diseases; soil; climate. Duhamel de Monceau : Disease progress curves. (1728 AD) Late 19th Century and forward… Kuhn (1858) - 1st textbook of plant pathology. Ward (1901): Book "Diseases in Plants" emphasized ecology (populations) of disease. Jones (1913) - Role of the environment. Gaumann (1946): "Principles of Plant Infection” -Disease spread, - Conditions leading to an epidemic, -'Infection Chain' (= disease cycle),-compare with medicine (disease of humans).
  • 8. Large(1952, andothers) -Disease progress curves -Crop losses -Disease assessment (measurement) Horsfall & Dimond (1960)- "Plant Pathology, Volume 3" -Populations -Inoculum density:disease relations -Spore dispersal -Analysis (mathematics) -Forecasting, prediction -Traditional definition ---> Modern definition Gregory(1963, 1973) "The Microbiology of theAtmosphere" -spore dispersal, disease spread Aerobiology Vanderplank (1963) (usedto be van der Plank) "Plant Diseases: Epidemics and Control" -Populations -Rates (dynamic processes) -Analysis, mathematics -Models, theory -Link epidemiology and control -Established the science of plant disease epidemiology Other pioneers: Zadoks (1960-1995), TheNetherlands Kranz (1968-1995),Germany Waggoner (1960-mid --1980s),USA S. Nagaranjan1983-India
  • 9. ELEMENTS OF AN EPIDEMIC 1) Host 2) Pathogen 3) Environment Interactions of the 3 main components are described by the disease triangle. The Disease Triangle Disease development is also affected by 4. Time 5. Humans Disease Tetrahedron Interactions of the 5 components are described by the disease pyramid.
  • 12. HOST FACTORS All plants can be considered hosts. o Degree of genetic uniformity. o Age – affects disease development depending on plant-pathogen interaction. There are different levels of susceptibility, which include: o Immune - cannot be infected. o Susceptible - can be infected. o Resistant - may or may not be infected.
  • 13. ENVIRONMENTAL FACTORS i. Moisture -Rain, dew, high humidity. -Dominant factor in diseases caused by oomycetes, bacteria & nematodes. ii.Temperature - Affects disease cycles of pathogens Diseasedevelopment is also affected by  Time factors • Season of the year • Duration & frequency of favorable temp. & rains • Appearance of vectors, etc.  Humans How HumansAffect Development of Epidemics • Site Selection & Preparation. • Selection of Propagative Material. • Introduction of Exotic Pathogens. • Cultural Practices. • Disease control measures.
  • 14. CLIMATE CHANGE & MICROBIAL INTERACTIONS i. Nitrogen deposition level, CO2 concentration and temperature are important factors affecting soil microbial communities (Garret et al., 2006). ii. Increased CO2 levels in the atmosphere have major consequences on carbon cycling and the functioning of various ecosystems. iii. Short-term and long-term changes in the abiotic conditions not only affect plant growth and productivity but also the populations of microorganisms living on plant surfaces. iv. Any change in phyllosphere microflora, affects plant growth and plants’ ability to withstand aggressive attack of pathogens.
  • 15. EFFECT OF TEMPERATURE Certain minimum temperature is required by both plants and pathogens to grow. Temperature affects the chain of events in disease cycles such as survival, dispersal, penetration, development and also reproduction rate for many pathogens. Generally high moisture and temperature favours and initiate disease development, as well as germination and proliferation of fungal spores of diverse pathogens (Agrios, 2005).
  • 16. EFFECT OF TEMPERATURE • Plants, as well as pathogens, require certain minimum temperatures to growandcarryout their activities. • At higher temperatures, pathogens become active and, they can infect plants andcausedisease. • Cankerdiseasesof perennial plants causedby:  fungi Nectria, Leucostoma (Cytospora), the oomycete Phytophthora  bybacteriasuchas Pseudomonas, • Infections beginanddevelop primarily in earlyspring or in thefall. • During these periods the temperatures are high enough for these fungi to growwell but aretoo low to allow optimum hostdevelopment.
  • 17. TEMPERATURE AFFECTS: 1. The number of spores formed in aunit plant area. 2. The number of spores released in a given time period.
  • 18. • Due to changes in temperature and precipitation, climate change may alter the growth stage, development rate, pathogenicity of infectious agents, and the physiology and resistance of the host plant (Charkraborty and Datta, 2003). • Sunlight affects pathogens due to the accumulation of phytoalexins or protective pigments in host tissue. • Host plants such as wheat and oats become more susceptible to rust diseases with increased temperature; but some forage species become more resistant to fungi with increased temperature (Coakley et al., 1999).
  • 19. • With increasing temperature spore germination of rust fungus Puccinia substriata increases (Tapsoba and Wilson, 1997). • In southern Germany, a northward shift of Cercospora beticola, leaf spot of sugar beeet was due to increasing annual mean temperature by 0.8-1°C (Richerzhagen et al., 2011). • Altered temperatures favour over-wintering of sexual propagules which increased the evolutionary potential of a population (Pfender and Vollmer (1999). • Conidia of powdery mildew have the ability to germinate even at 0% relative humidity (RH) (Yarwood, 1978). • Conidia of Erisiphe cichoracearum germinate at temperature from 7 to 32°C with a RH of 60 to 80% (Khan and Khan, 1992); and spores of Erysiphe necator germinate at temperatures from 6 to 23°C with a RH from 33 to 90 % (Bendek et al., 2007).
  • 20. • Phytophthora infestans, late blight of potato and tomato, infects and reproduces most successfully at high moisture when temperatures are between 7.2°C and 26.8°C. • Infection of Eucalyptus sp. by Phytophthora cinnamomi due to increased soil temperature of 12-30°C (Podger et al., 1990). • Even the incidence of virus and other vector borne diseases also alter. Mild and warmer winters make aphids easy to survive thus spreading Barley yellow dwarf virus (BYDV) and also increase viruses of potato and sugar beet (Thomas, 1989; Mackerron et al., 1993).
  • 21. RISK ANALYSIS STUDIES ON THE EFFECTS OF CLIMATE CHANGE STUDY RESULT REFERENCE • In the UK, the effects of climate change on Phoma (Leptosphaeria maculans) were assessed. Epidemics will not only increase in severity but also spread northwards by the 2020s. Evans et al., 2007 • Future scenarios of downy mildew on grapevine (Plasmopara viticola) were simulated from the results of two climate change models. The results suggested that the incidence of disease would increase and the production of grapes in northwestern Italy would decrease. Predicted an increase of the disease pressure in each decade to consequence of more favorable temperature conditions. Salinari et al., 2006 • A model to assess the severity of Phytophthora infestans under climate change was developed A marked shift of the disease in the infestation pressure to higher altitude Kocmankova et al., 2007
  • 22. STUDY RESULT REFERENCE The effects of elevated levels of CO2 and temperature on the incidence of four major chili pepper diseases  (Anthracnose (Colletotrichum acutatum)  Phytophthora blight (Phytophthora capsici)) and • two bacterial diseases (bacterial wilt (Ralstonia solanacearum) and bacterial spot (Xanthomonas campestris pv. vesicatoria)) were determined. Elevated CO2 and temperature significantly increased the incidence of two bacterial diseases. Anthracnose decreased and Phytophthora blight slightly increased. Shin and Yun, 2010
  • 23. A summary of the influence of elevated Temperature on some Host and Pathogen Interaction CROP/HOST DISEASE/PATHOGEN CLIMATE CHANGE CHANGE IN DISEASE SEVERITY AUTHOR/REFERENCE Wheat Stripe rust – Puccinia striiformis Elevated average annual temperature Decrease Yang et al., 1998 Wheat Dwarf bunt- Tilletia controversa Elevated temperatures Increase Boland et al., 2005 Wheat Wheat Stripe rust – Puccinias triiformis Higher Temperature Increase Milus et al., 2006 Citrus Anthracnose- Colletotrichum acutatum Elevated Temperatures Increase Jesus Junior et. al., 2007 Potato Late blight – Phytophthora infestans Elevated temperatures causing earlier seasons Increase Hannukkala et al., 2007 Papaya Asperisporium caricae Elevated temperatures and lower relative humidity Decrease Jesus Junior et. al., 2007 Pineapple Fusarium subglutinans Elevated temperatures Decrease Matos et al., 2000 Coffee Meloidogyne incognita Elevated temperatures Increase Ghini et al., 2008
  • 24. EFFECT OF CO2 a. Increased size of plant organs, leaf area, leaf thickness, more numbers of leaves, higher total leaf area/plant, stems and branches with greater diameter are resulted from increased CO2 levels (Bowes, 1993 and Pritchard et al., 1999). b. Dense canopy favours the incidence of rust, powdery mildew, Alternaria blight, Stemphylium blight and anthacnose diseases. c. Higher CO2 concentrations induce greater fungal spore production. Increased CO2 also enhances photosynthesis, increased water use efficiency and reduced damage from ozone (von Tiedmann and Firsching, 2000); and leaf area, plant height and crop yield are increased at higher doses of CO2 (Eastburn et al., 2011). d. The physiological changes on the host plant due to increased CO2 can conversely result in increase host resistance to pathogens (Coakley et al., 1999).
  • 25. EFFECT OF C02 i. Under elevated CO2 conditions, potential of dual mechanism i.e., reduced stomata opening and altered leaf chemistry results in reduced disease incidence and severity in many plant pathosystems where the pathogen targets the stomata (Mcelrone et al., 2005). ii. In soybean, elevated concentration of CO2 and O3 altered the expression of 3 soybean diseases, downy mildew (Perenospora manshurica), brown spots (Septoria glycines) and sudden death syndrome (Fusarium virguliforme) (Eastburn et al., 2010). iii. Elevated CO2 also leads to production of papillae and accumulation of silicon by barley plants at the site of appressorial penetration of Erysiphe graminis and changed leaf chemistry that decrease susceptibility to the powdery mildew pathogen (Hibberd et al., 1996).
  • 26. EFFECT OF INCREASED CO2 CONCENTRATIONS ON PATHOGENS STUDY RESULT REFERENCE • The effect of elevated concentrations of CO2 on the infection of barley by Erysiphe graminis was determined. The percentage of conidia that progressed to produce colonies was lower in plants grown in 700 than in 350ppm CO2. Hibberd et al. (1996) • Interactive effects of elevated CO2 and O3 levels on wheat leaves infected with leaf rust fungus Puccinia triticina were described. Elevated CO2 increased the photosynthetic rates of the diseased plants by 20 and 42% at the ambient and elevated ozone concentrations, respectively. Tiedemann and Firstching (2000). • The effects of elevated CO2 concentrations on the development of Phytophthora parasitica (root rot) in tomato were evaluated. The extra CO2 completely counterbalanced the negative effect of the pathogenic infection on overall plant productivity. Jwa and Walling (2001). • Pyricularia oryzae Cavara and Rhizoctonia solani Kühn were evaluated. Rice plants grown in an elevated CO2 concentration were more susceptible to leaf blast than those in ambient CO2. Kobayashi et al. (2006).
  • 27. STUDY RESULT REFERENCE • The effects of carbon dioxide (CO2) and ozone (O3) on three soybean diseases (downy mildew, Septoria and sudden death syndrome) were determined in the field. Changes in atmospheric composition altered disease expression. Elevated CO2 reduced downy mildew disease severity. But increased brown spot severity and without effect in sudden death syndrome. Eastburn et al. (2010). • The response of tobacco to potato virus Y was evaluated. The titre of viral coat-protein was markedly reduced in leaves under these conditions at both nitrogen levels. The accumulation of phenylpropanoids, may result in an earlier confinement of the virus at high CO2. Matros et al. (2006). • The germination rates of conidia of C. gloeosporioides were determined. spore germination was reduced and extended incubation period was at 700 ppm, and Anthracnose severity was reduced. Chakraborty et al. (2002).
  • 28. EFFECT OF MOISTURE • It influences the initiation and development of infectious plant diseasesin many interrelatedways. Moisture is indispensablefor:  The germination of fungalspores  Penetration of the host by the germ tube  Activation of bacterial, fungal, and nematode pathogens before they caninfect theplant.  The spread of pathogens on the same plant and from one plant to another • Moisture increases the succulence of host plants and thus their susceptibility to certain pathogens, which affects the extent and severity ofdisease.
  • 29. EFFECT OF MOISTURE With increased temperature extreme rainfall events and higher atmospheric water vapour concentrations take place. i. These encourage the crops to produce healthier and larger canopies that retain moisture as leaf wetness and RH for longer periods and results in condition conducive for pathogens and diseases such as late blights and vegetable root diseases including powdery mildews (Coakley et al., 1999). ii. High moisture favours foliar diseases and some soil borne pathogens such Phytophthora, Pythium, R. solani and Sclerotium rolfsii. iii. Drought stress affect the incidence and severity of viruses such as Maize dwarf mosaic virus (MDMV) and Beet yellows virus (BYV) (Olsen et al., 1990 and Clover et al., 1999).
  • 30. EFFECT OF WIND Wind influences infectious plantdiseases: • primarily by increasing the spread of plant pathogens and the number of wounds on host plants. • to a smaller extent, by accelerating the drying of wet surfaces of plants. • fungi, bacteria, and viruses that are spread either directly by the wind or indirectly by insect vectors that can themselves be carried over long distances by thewind. • wind-blown rain helps release spores and bacteria from infected tissue and then carries and deposits them on wet surfaces of plants, which, if susceptible, can be infected.
  • 31. EFFECT OF LIGHT • The intensity and the duration of light may either increase or decrease the susceptibility of plants to infection. • Low light produces etiolated plants, which increases the susceptibility of plants to non obligate parasites. Tomato plants to Botrytis or to Fusarium. • Reduced light intensity generally increases the susceptibility of plants tovirus infections. • Low light intensities following inoculation tend to mask the symptoms of somediseases.
  • 32. EFFECT OF SOIL pH & SOIL STRUCTURE • The pH of the soil is important in the occurrence and severity of plant diseases caused by certain soil borne pathogens.  Clubroot of crucifers (Plasmodiophorabrassicae) severe -pH 5.7 drops between pH5.7 -6.2 and completely checked -pH7.8.  Cotton root rot fungus (Phymatotrichopsis omnivora) exists only in soils contain relatively high concentrations of calciumcarbonate.
  • 33. EFFECT OF HOST-PLANT NUTRITION Nutrition affects the rate of growth and the state of readiness of plants. • Nitrogen: abundance results in the production of young, succulent growth, a prolonged vegetative period, and delayed maturity of the plant, make the plant more susceptible topathogens. • Phosphorus: increase resistance by improving the balance of nutrients in the plant or by accelerating the maturity of the crop and to escape infection by pathogens that prefer younger tissues.
  • 34. Potassium : • Have a direct effect on pathogen establishment and development in thehost. • And an indirect effect on infection by promoting wound healing. • Potassium also increases resistance to frost injury. Calcium: Effects the composition of cell walls and their resistance to penetrationby pathogens. Various micronutrients (Fe, Cu,Mn,Mg,Si) showed decreased infection when levels of nutrients increased.
  • 35. EFFECTOF HERBICIDES AND AIR POLLUTANTS: i. The direct effects may include stimulation or retardation of the growth of the pathogen or in the susceptibility of the host. ii. Indirect effects include effect on activity of soil microflora, elimination or selection of the pathogen by certain alternate hosts, or alteration of the microclimate of the crop plant canopy. iii. ozone, can affect a pathogen and sometimes the disease it causes. The rate of infection is reduced if the exposure to ozone is early but is increased if exposure occurs late.
  • 36. EFFECT OF CLIMATE CHANGE ON VECTOR- BORNE DISEASES i. The risk of vector-borne disease at the local and regional level is limited by the climatic requirements of disease vectors (Malmstrom et al., 2011). ii. Both host plant and insect-vector populations are affected by climate change and spread the plant viruses (Jones, 2009). iii. Climate change influences the primary infection of the host, the spread of the infection within the host and/or the horizontal transmission of the virus to new hosts by the vector along with phenology and physiology of the host thereby affect its virus susceptibility and virus ability to infect. iv. Climate change has various effects on vectors like modification of vector phenology, vector’s over-wintering, density, migration and its stability.
  • 49. RESEARCH NEEDS 1. The effectiveness of disease management strategies. Assessing current management strategies and proposing alternatives will prepare us for the challenge of climate change. This will allow our mitigation measures to be more efficient and adaptable to change. 2. The risk of disease must be analyzed to determine the geographical distribution and modification of diseases due to climate change. 3. Plant diseases and crops must be modeled. Mathematical models can be used to perform quantitative analysis of the phytosanitary problems. They provide a very powerful tool to understand and represent interactions among weather, crop and disease variables (Allman and Rhodes, 2004). 4. Mathematical models can help to assess the probability of introduction, reproduction and dispersion of diseases, and the magnitude of their effects on crops yield and quality in current scenarios and under climate change. 5. Factors limiting the survival of pathogens should be characterized (e.g., temperature, humidity, CO2, O3 and radiation).
  • 50. CONCLUSION • Climate change is an important phenomenon that affects agricultural production. By anticipating the future, we can prepare ourselves for problems caused by climate change, especially those related to agricultural activities. • Global warming may modify areas affected by pests and diseases, studies must be performed to assess pest and disease stages under the effects of climate change, determine the magnitude of disease and identify measures to minimize the risk of infection. • Exposure to altered atmospheric conditions can modify fungal disease expression. Studies had shown that exposure at elevated CO2 increases disease incidence or severity in some cases but in other cases decreased.
  • 51. • These highlight how the host–pathogen interactions make it difficult to devise general principles that govern changes across fungal pathosystems. So increase or decrease disease will be in function of the host and pathogen. • Climate change may affect the actual, spatial and temporal distribution of diseases; however, the magnitude of these effects remains unclear. • Disease risk analysis based on host-pathogen interactions should be performed, and research on host response and adaptation should be conducted to understand how an imminent change in the climate could affect plant diseases.