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Environmental pollution is a serious menace to all kinds of life and threatens our fragile environment that is so vital for our survival.
The air pollutants cause direct and indirect effect on microbial community.
Air pollution damage to vegetation has been recognized for more than 125 years. Air pollutants are a fact of modern life. The susceptibility of pollution stressed plants to microbial
pathogens may be altered and the disease development may be influenced. Interactions between air pollutants and plant pathogens on a given host may affect pathogenesis.
Thus plant diseases may be either enhanced or
Urbanization, industrialization, transportation, and energy consumption are increasing at an unprecedented scale in big cities because the infrastructure development in major cities has not kept pace with the population influx, thereby giving rise to poor planning, faulty traffic systems and
blatant disregard poor vehicle maintenance.
Air pollution is said to exist when a wide range of
inorganic gases, organic compounds, inorganic metallic substances and smoke particles are discharged into the atmosphere by the motor vehicles, factories, power plants, home furnaces and waste incineration plants.
The diverse emissions into the atmosphere bring about
qualitative or quantitative changes in the normal composition of the air that may adversely affect human health and plant life.
Some times natural causes such as forest or grassland
Air pollutants are any aerial substances that have the potential to cause adverse effects on plants, animals or cultural assets.
At present more than 300 substances are known which can be emitted into the air, and are significant as air
Environmental pollution is a product of the anthropogenic activities.
Human has unconsciously interfered with the environment so much that its deterioration in many areas has reached alarming proportions, basically due to massive industrial
development, rapid increase of automotives and exponential growth of world population and its food consumption.
Between 100 and 200 million tons of man-made air pollutants are released each year into the atmosphere in the United States. According to U.S. EPA’s
Inorganic Pollutants
OZONE (O
3)
Ozone is an active form of oxygen that causes a variety of symptoms, including tissue collapse, interveinal necrosis, and markings on the upper surface of leaves known as stipple (pigmented yellow, light tan, red brown, dark brown, red, black, or purple), flecking (silver, or bleached straw-white), mottling, chlorosis or bronzing, bleaching, and a marginal rolling and scorching of leaves.
Growth is stunted.
Flowering and bud formation are depressed.
Young plants generally are the most sensitive to ozone; mature plants, relatively resistant.
Ozone is brought down from the stratosphere by
turbulence in strong vertical down-drafts during severe electrical storms; more important, it is produced when sunlight reacts with nitrogen oxides and hydrocarbons formed by refuse burning and combustion of coal or petroleum fuels, especially the exhaust gases from internal-combustion engines.
When oxidant levels in the air are high, more than 90 percent is ozone.
Exposure of sensitive plants for 4 to 6 hours at levels of
0.02 to 0.04 parts per million (ppm) of air or more will produce injury patterns.
Ozone inhibits a number of pathogenic fungi or their effects are pronounced by it.
Facultative parasites are affected more than facultative saprophytes.
Manning et al. (1970) investigated invasion of potato leaves by Botrytis cinerea under the stress of ozone.
Invasion of the leaves by the fungus was enhanced when plants were exposed to (0.15-0.25 ppm ozone) for 6-8h.
Kochhar et al. (1982) studied the effect of single acute
ozone exposure (0.3 ppm for 2 h) of clover on pathogenesis of Rhizoctonia solani followed by 0.04-0.16 ppm through out the season.
The effect of sulphur dioxide (0.1 and 0.2 ppm) for
Fluorida (F)
The typical injury by gaseous (primarily hydrogen fluoride (HF) and silicon tetrafluoride (SiF4) or particulate fluorides is a yellowish mottle to a wavy, reddish-brown or tan
“scorching” at the leaf margins and tips of broadleaved plants, and a “tipburn” of grasses and conifers.
A narrow, chlorotic to dark-brown band often occurs between living and dead tissue.
Leaves and fruits, such as apple, apricot, citrus, fig, peach, plum, and prune, may fall prematurely.
Fruits may soften or become necrotic at the blossom end.
Sulfur Dioxide (S02)
The exposure of succulent, broadleaved plants to SO2 (and its byproduct, sulfuric acid) usually results in dry, papery
blotches that are generally white to tan or straw-colored and marginal or interveinal.
Both the upper and lower leaf surfaces are affected. The leaf veins normally remain green.
Chlorosis (yellowing) and a gradual bleaching of the surrounding tissues is fairly common.
Growth suppression, reduction in yield, and heavy, premature defoliation may also occur.
Full-grown and nearly full-grown leaves and young plants are most susceptible to SO2. Young and old leaves are
Chlorine (Cl
2)
Chlorine injury is somewhat similar to that caused by sulfur dioxide and fluorides, in that it is marginaland interveinal.
Two types of damage generally can occur:
(1) with broadleaved plants, necrotic, bleached, or tan-to-brown areas that tend to be near the leaf margins, tips, and between the principal veins.
Impact of Air Pollution on Plant Diseases
Air pollutants directly toxic to the pathogens possible impair their growth and reproduction and thereby partially or wholly inhibit the diseases.
Air pollutants on the other hand, by modifying the host physiology may render it more susceptible to infection and pathogenic damages.
Atmospheric pollutants may adversely affect the spore
Air pollutants cause specific diseases in plants thus behave as plant pathogens.
In nature plants remain exposed to multiple pathogenic situations.
These pathogens to which plants remain exposed interact in nature and the ultimate effect on the host is the result of their interactive actions.
Secondly, air pollutants develop relationship with various kinds of biotic pathogens influencing the incidence and
intensity of the biotic diseases.
It these two groups of the pathogens abiotic (e.g. air
pollutants) and biotic (e.g. fungi, bacteria, viruses etc.) co-exist in a common pathosystem, it is quite apprehensible that they may become vulnerable to greater pathogenic damages caused by the biotic pathogens or the plants
infected with biotic pathogens may become more sensitive and suffer greater damages caused by the pollutants.
Conidial germination of the powdery mildew fungi was reduced at both the concentrations of sulphur dioxide. With increase in the duration of exposure, a
corresponding decrease in the conidial germination occurred.
Spore germination of some fungi like Phytophthora infestans was inhibited by SO2.
Laurence et al. (1979) reported 38% decrease in the number of lesions caused by Helminthosporium maydis
on maize exposed to 0.15 ppm SO2, 14 h daily for 8
days, before inoculation.
Couey (1965) observed 60% reduction in spore
germination of Alternaria spp. with treatment of ppm SO2
According to Heagle (1982) stimulated acid rain caused inhibition of growth of Cronartium fusiforme on leaves of yellow oat inoculated with aeciospores.
Lawry (1977) studied the fungal population in soils at the sites exposed to acid rain from strip-mines and observed a decrease in fungal species diversities.
Sharp (1967) determined that high ionic concentrations in the atmosphere reduced the germination of Puccinia
Pengendalian
The solution to the air pollution problem is complex and involves:
1.Enforced use of special, adjusted control devices on motor vehicles and aircraft.
2. Stopping emissions at the source (the smoke stack or combustion chamber) by such “scrubbing systems” as electrostatic precipitators, filtering devices including fabric filters, absorption equipment, gravity
settling chambers, sonic and ultrasonic collectors, and byproduct recovery. 3. Public awareness and adequate enforcement of federal, state, and local legislation.
4. Plant breeding and selection of less susceptible crops for critical areas. 5. Using less susceptible plants or cultivars.
Ozone inhibits a number of pathogenic fungi or their effects. ozone enhanced the predisposition of the leaves of plants to
B. cincerea inoculated one day after exposure.
The rate of enhancement depended on the level of O3
induced injury, which was influenced by the cultivar, leaf and ozone concentrations.
Trifoliate leaves of all the cultivars were less predisposed to the fungus than the primary leaves.
The effect of sulphur dioxide was observed on conidial germination of some powdery mildew fungi.
Conidial germination of the powdery mildew fungi was reduced at both the concentrations of sulphur dioxide.
With increase in the duration of exposure, a corresponding decrease in the conidial germination occurred.
Spore germination of some fungi like Phytophthora infestans was inhibited by SO2.
Exposure 0.04 ppm sulphur dioxide for 24-72h continuously caused reduction in spore germination, penetration and
hyphal production of Microsphaera alni infecting lilac leaves. 38% decrease in the number of lesions caused by
Helminthosporium maydis on maize exposed to 0.15 ppm SO2, 14 h daily for 8 days, before inoculation.
Acid rain caused inhibition of growth of Cronartium fusiforme on leaves of yellow oat inoculated with aeciospores.
The exposure of plant foliage to acid rain has also implications on root diseases.
