cyanobacterial species Synechocystis PCC 6803 and Anabaena variabilis ATCC
29413 (Powell et al. 1991). Next to glyphosate, atrazine is a commonly used
nitrogen-rich herbicide which inhibits the photosynthesis of weed plants. Atrazine
is only weakly adsorbed to soil particles during treatment and thus leaves the field
mainly as runoff water. Moreover, they can migrate from upper soil surface to lower
ground and reach underground water. Hence, it pollutes soil as well as water.
Atrazine basically inhibits photosystem II (PSII) in many plant species, algae and
cyanobacteria. Novel atrazine-resistant gene has been identified in naturally occurring cyanobacteria, but they lack degradation and catabolism mechanism. However,
trace amount of ammonia compounds was identified in cyanobacteria tank treated
with atrazine (Sajjaphan et al. 2002).
Cyanobacteria not only degrade and accumulate pesticides in soils but also
replace that use by their potential bioactive compounds. Cyanobacteria were able
to produce a wide variety of bioactive compounds which possess antagonistic
activity against competitive organisms. Hence, these bioactive compounds can be
commercially utilized for pest and disease management in agriculture. Novel metabolites from Fischerella sp. were found to have insecticidal activity against larval
grazers (Becher and Jüttner 2006). Ethanolic extract of Nostoc carneum showed
insecticidal activity against cotton leafworm Spodoptera littoralis, and the crude was
found to comprise of fatty acids and terpenes. Extracellular metabolites of Nostoc
muscorum and Oscillatoria sp. reduce the severity of purple blotch disease of onion
caused by Alternaria porri through its antifungal activity, and their metabolites were
mostly comprised of phenols and alkaloids. Precisely the most prevalent compounds
in their filtrates were identified to be beta ionone, norharmane and α-iso-methyl
ionone, and other trace compounds were piperazine derivatives, isocyclocitral,
α-trans-sequicyclocitral, phytol, oleic acid, methyl palmitate, linoleic acid methyl
ester, myristic alcohol and palmityl chloride (Abdel-Hafez et al. 2015). Antagonistic
activity of two commercially available cyanobacterial compounds, viz. oligo-mix
and weed-max on root rot fungal pathogens Alternaria solani, Fusarium solani,
F. oxysporum, Rhizoctonia solani, Sclerosium rolfsii, Sclerotinia sclerotiorum, and
S. minor, was tested individually and also co-inoculated with antagonistic
bio-control agent. Under both the situations, it showed efficient growth suppression
of fungal pathogens (El-Mougy and Abdel-Kader 2013).
5.3.2 Chemical Fertilizers
Chemical fertilizers are used to enhance the plant growth and yield in farm fields.
Massive application of fertilizers leads to several soil-related problems such as soil
acidification, ground water pollution and depletion in soil microorganism. In general, soil possess tremendous amount of natural nutrients, and it is sufficient to have
good plant growth. Plant could not uptake all forms of nutrients, there are certain
nutrient kind present in unavailable form. Clever utilization of nutrients present in
farm soil will reduce the risk of soil contamination. Microbes are used as
144
K. G. Sabarinathan et al.
29413 (Powell et al. 1991). Next to glyphosate, atrazine is a commonly used
nitrogen-rich herbicide which inhibits the photosynthesis of weed plants. Atrazine
is only weakly adsorbed to soil particles during treatment and thus leaves the field
mainly as runoff water. Moreover, they can migrate from upper soil surface to lower
ground and reach underground water. Hence, it pollutes soil as well as water.
Atrazine basically inhibits photosystem II (PSII) in many plant species, algae and
cyanobacteria. Novel atrazine-resistant gene has been identified in naturally occurring cyanobacteria, but they lack degradation and catabolism mechanism. However,
trace amount of ammonia compounds was identified in cyanobacteria tank treated
with atrazine (Sajjaphan et al. 2002).
Cyanobacteria not only degrade and accumulate pesticides in soils but also
replace that use by their potential bioactive compounds. Cyanobacteria were able
to produce a wide variety of bioactive compounds which possess antagonistic
activity against competitive organisms. Hence, these bioactive compounds can be
commercially utilized for pest and disease management in agriculture. Novel metabolites from Fischerella sp. were found to have insecticidal activity against larval
grazers (Becher and Jüttner 2006). Ethanolic extract of Nostoc carneum showed
insecticidal activity against cotton leafworm Spodoptera littoralis, and the crude was
found to comprise of fatty acids and terpenes. Extracellular metabolites of Nostoc
muscorum and Oscillatoria sp. reduce the severity of purple blotch disease of onion
caused by Alternaria porri through its antifungal activity, and their metabolites were
mostly comprised of phenols and alkaloids. Precisely the most prevalent compounds
in their filtrates were identified to be beta ionone, norharmane and α-iso-methyl
ionone, and other trace compounds were piperazine derivatives, isocyclocitral,
α-trans-sequicyclocitral, phytol, oleic acid, methyl palmitate, linoleic acid methyl
ester, myristic alcohol and palmityl chloride (Abdel-Hafez et al. 2015). Antagonistic
activity of two commercially available cyanobacterial compounds, viz. oligo-mix
and weed-max on root rot fungal pathogens Alternaria solani, Fusarium solani,
F. oxysporum, Rhizoctonia solani, Sclerosium rolfsii, Sclerotinia sclerotiorum, and
S. minor, was tested individually and also co-inoculated with antagonistic
bio-control agent. Under both the situations, it showed efficient growth suppression
of fungal pathogens (El-Mougy and Abdel-Kader 2013).
5.3.2 Chemical Fertilizers
Chemical fertilizers are used to enhance the plant growth and yield in farm fields.
Massive application of fertilizers leads to several soil-related problems such as soil
acidification, ground water pollution and depletion in soil microorganism. In general, soil possess tremendous amount of natural nutrients, and it is sufficient to have
good plant growth. Plant could not uptake all forms of nutrients, there are certain
nutrient kind present in unavailable form. Clever utilization of nutrients present in
farm soil will reduce the risk of soil contamination. Microbes are used as
144
K. G. Sabarinathan et al.