IMPACT OF CLIMATIC PARAMETERS ON PATHOGEN,

INSECT PESTS AND CROP PRODUCTIVITY

Santosh.BRAM/14-32

Dept. Of Crop Physiology

IMPACT OF CLIMATIC PARAMETERSPATHOGENS

• Plant diseases occur in all parts of the world where plants grow.

• For a disease to occur and to develop optimally, a combination of three factors must be present:

susceptible plant, infective pathogen and favorable environment.

EFFECT OF TEMPERATURE :• Plants, as well as pathogens, require certain minimum

temperatures to grow and carry out their activities.• At higher temperatures, pathogens become active and, they can

infect plants and cause disease.• canker diseases of perennial plants caused by fungi Nectria, Leucostoma (Cytospora), the oomycete

Phytophthora by bacteria such as Pseudomonas,• infections begin and develop primarily in early spring or in the

fall.• During these periods the temperatures are high enough for

these fungi to grow well but are too low to allow optimum host development.

Temperature affects • the number of spores formed in a unit plant

area • and the number of spores released in a given

time period

EFFECT OF MOISTURE :• It influences the initiation and development of infectious

plant diseases in many interrelated ways.Moisture is indispensable for the germination of fungal spores penetration of the host by the germ tube activation of bacterial, fungal, and nematode pathogens

before they can infect the plant. 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 of disease.

EFFECT OF WIND :Wind influences infectious plant diseases• 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 the wind.• 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 to virus infections.• Low light intensities following inoculation tend to

mask the symptoms of some diseases.

EFFECT OF SOIL PH AND 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 (Plasmodiophora brassicae) severe -pH 5.7

drops between pH 5.7 -6.2 and completely checked -pH 7.8.

• Cotton root rot fungus (Phymatotrichopsis omnivora) exists only in soils contain relatively

high concentrations of calcium carbonate.

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 to pathogens.

• 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 the host• 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 penetration by pathogens.Various micronutrients (Fe, Cu,Mn,Mg,Si) showed

decreased infection when levels of nutrients increased.

EFFECT OF HERBICIDES and AIR POLLUTANTS:• The direct effects may include stimulation or retardation of the growth of the pathogen or in the

susceptibility of the host.• 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.

• Air pollutants cause various types of direct symptoms on plants exposed to high levels of pollutants.

• 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.

IMPACT OF CLIMATIC PARAMETERS onINSECT PESTS

• Abiotic factors play a vital role in the development,longevity,reproduction and fecundity of insect pests.

TEMPERATURE:• The insects are poikilothermic –their body

temperature follows surrounding medium.• Preferred temperature or temperature preferendum• As long as species of optima for development are

not exceeded, there might be positive direct responses of insects to increasing temperature conditions, such as enhanced reproductive potential.

• Temperatures above the specific optimum range lead to decreased growth rates, reduced fecundity and increased rates of mortality.

(Source: Das et al., 2011; Parmesan, 2006; Bale et al., 2002; Thomas et al., 2004; Trumble and Butler, 2009)

• Exposure to lethal low or high temperaturs : instant killing loss of reproductive capacity lethal at ecdysis or pupation lead to dormancy /hibernation/ aestivation

Moisture (Precipitation and Drought):• The water content of insects :50-90%/w.• Humidity preferendum• Increase in the frequency of flooding of fields could tend

to suppress some soil dwelling insect populations. Quite the opposite, drier

conditions would have the opposite effect.• Enhanced summer rainfall and drought conditions on soil

dwelling Agriotes lineatus (wireworms) promote rapid increase in the population of wireworms in the upper soil.

• African chironomid midge (polypedilum vandesplanki) can tolerate dehydration for years.

Exposure to excessive moisture will be lethal by:• Reduce Normal development and feeding

activity• increase disease causing micro organisms • mortality• reduce cold hardiness (cuticle damage)

Oxygen and CO2 :• The combined effect of higher temperatures and CO2

concentration could have high effects on overall growth and development of insects.

• Several insect pests increase their feeding on soybeans in high CO2 atmospheres.

• This is thought to be the result of insect feeding stimulation caused by increased simple sugars in the leaves of the plants. (plants grown in high CO2 atmosphere have a higher C:N ratio).

• Pests increase their feeding in order to fulfill their metabolic needs for nitrogen (Petzoldt and Seamann, 2012).

• In increased CO2 conditions spiracles of insects tend to remain open, lead t excessive water loss.

(Source: Das et al., 2011; Coviella and Trumble, 2000; Chen et al., 2005; Osbrink etal., 1987; Awmack et al., 1997; Roth and Lndroth, 1995)

LIGHT :• Light is an important ecological factor for many

biological processes of insects.• Light acts in regulation and sychronizing life

cycles• A non-lethal factor• Phototaxis : is oriented locomotory movement

towards or away from the light.• Phototropism: in sessile insects, which is light

oriented growth mechanism. this may be of positive or negative response.

Photoperiodism influences• Rhythms of locomotion• Feeding • Adult emergence• Mating and oviposition• Moulting and growthLack of favourable photoperiod leads to

diapause state

AIR :• The air currents carry aphids, leafhoppers and

scale insects (instrumental in dispersal).• Severe wind coupled with heavy rains may

cause mortality and increase the gradient of water vapour conc. and increase rate of evaporation

EDAPHIC FACTORS:• Soil texture, moisture, drainage, chemical

composition and topography affect distribution and abundance of insects• Cut warm Agrotis ipsilon larvae live in soil of

light texture• Chemicals (abundance and distribution) mineral deficiencies (plant deficiencies lead to

poor growth of insects) N deficiency reduce productivity of some insects

IMPACT OF CLIMATIC PARAMETERSCROP PRODUCTIVITY :

• Quantitative measure of crop yield in given measured area of field.

• Many plant and environmental factors influence photosynthesis as well as crop productivity such as light, CO2, temperature, availability of water

LIGHT:• Solar radiation is the primary driver of plant

photosynthesis• increment in light elicits a proportional

increase in photosynthetic rate

• The Photon flux density at which net CO2 exchange in the leaf is zero is called light compensation point.

sun plants : 10-20 u mol m-2 S-1 shade plants : 1-5 u mol m-2S-1 (low

respiration rates)

TEMPERATURE :• Temperature has major effects on

photosynthesis and respiration, plant growth and phenological development.

• At low temperatures severely growth is limited, whereas

• At high temperatures the stomata on the leaves can close so as to limit gaseous exchange, water loss, and consequently active growth.

• The bell-shaped responses to temperature• C4 plants generally have higher temperature optima than C3 plants (lower

rates of photorespiration in C4 plants).

• Temperature controls phenological changes in development from germination and seedling emergence, through vegetative growth to floral initiation and reproductive growth.

• Intracellular freezing: (-7ºC) tissue death resulting from the combined

effects of membrane injury, cytoplasm dehydration and protein denaturation.

• Frost hardiness of plant cells involves cell size, wall thickness, osmotic pressure of

cell sap and membrane properties.

Carbon dioxide :• The CO2 compensation point, the CO2

concentration at which CO2 fixation by photosynthesis balances CO2 loss by respiration and net CO2 is zero.

• Plants with C4 metabolism have a CO2 compensation point of zero or nearly zero (CO2 compensation point of

C3 plants is 35 – 50 ppm, C4 plants 0 – 10 ppm.)

WATER :• When water becomes limiting, cell expansion

is first retarded so that growth is reduced.• stomata begin to close and CO2 uptake is

restricted.• retarded leaf expansion and because of

restricted CO2 absorption.

Other factors :• Factors like herbicides, salinity and water

logging also affect the rate of photosynthesis and productivity.

• Herbicides by interrupting photosynthetic electron flow(Ex. Paraquat, diuron).

• When light reaction is stopped the dark reaction does not happen and thus CO2 is not fixed as carbohydrate. Thus weeds die by starvation.

Thank Q