• Growth boosters: TiO 2 -NPs interact with plants and
influence their metabolic activities, plant growth and
development. Besides this, they can also alter soil properties like physico-chemical and biological which can
improve soil health and its quality. So, they can be used
as nanofertilizers and nanosensors.
• Protecting agents: TiO 2 -NPs are found to be effectively
used in plant protection against various stresses like cold
stress, drought, salinity stress, heavy metal toxicity and
others. Also, due to their unique properties and chemical
activities they can be utilized for crop protection from
pests and pathogens. So, they can be utilized as bactericides, nanoherbicides and nanopesticides.
For the achievement of above-mentioned benefits, TiO 2 -
NPs are used as carrier agents for smart targeted delivery of
various nutrients and biological molecules which is supposed to get indulged within soil and plant. The detailed
discussion and studies to support the utilization of TiO 2 -NPs
in order to promote agriculture production are given in the
following sections (Table 3).
4.1 Nanoparticles as Growth Promoter
With an objective to promote TiO 2 -NPs use for agricultural
applications, their effects in seed germination as well as in
seedling growth have been investigated in several crop
plants (Tables 2 and 3A) and found contradictory (i.e., both
positive and negative results). There is no agreement on the
responses of plants to TiO 2 -NPs exposure because different
plant species, their growth stages and treatment conditions
seem to display diverse responses (Cox et al. 2016;
Mukherjee et al. 2016; Mattiello et al. 2015; Tan et al. 2018;
Chaudhary and Singh 2020).
TiO 2 –NPs have been reported to promote crop yield by
improving seed germination, growth and development of
wide varieties of plants, viz. Cicer sp., cabbage, Brassica
napus, cucumber, spinach, onion, soybean, maize, tomato,
wheat and many more. Entry of NPs into the seeds plays a
critical significant role in increasing the rate of seed germination (Fan et al. 2016). The priming of seeds with TiO 2 –NPs
could promote seed germination and plant growth by
increasing chlorophyll contents, photosynthesis performance
by improving light absorbance, activate the photochemical
reaction, induction of rubisco activase and nitrate reductase
activity and water conduction (Zheng et al. 2005; Raliya et al.
2015a; Singh et al. 2016). Studies have reported that exposure
to definite doses of TiO 2 -NPs accelerated germination in aged
seeds of spinach and the germination time in Triticum aestivum seeds (Zheng et al. 2005; Feizi et al. 2012; Jiang et al.
2017). Size of NPs plays a very important role in its behavior,
toxicity and reactivity. A treatment of TiO 2 -NPs (*20 nm) to
Canola seeds, improved seed germination and seedling vigor
at 2000 mg l
−1 concentration (Mahmoodzadeh et al. 2013).
Lu et al. (2006) reported an improvement in seed germination
and growth at low concentrations of mixture of TiO 2 -NPs and
nSiO 2.
By virtue of their photocatalytic properties, TiO 2 -NPs
induce oxidation–reduction reactions and increase growth
and development of plant (Hong et al. 2005; Lei et al. 2008;
Li et al. 2015). Besides, photo-attenuation activity of TiO 2 -
NPs protects the chloroplasts from photo-oxidation and
aging and hence, extends the photosynthetic activity of
chloroplasts (Yang et al. 2008). Overall, seed priming and
application of TiO 2 -NPs via roots or leaves (soil amendment
or foliar spray) at low concentrations could be a better
alternative to improve the quality, biomass and yields of
many cultivars (Moaveni et al. 2011; Morteza et al. 2013;
Raliya et al. 2015a, b; Rafique et al. 2018). Du et al. (2011)
had demonstrated that the concentrations of TiO 2 -NPs significantly affect the enzymatic activities of soil enzymes
which in turn affect the soil properties and health. Therefore,
TiO 2 -NP can be utilized as nanofertilizers to improve agriculture output.
Besides, they have a potential to be used as nanosensors
to detect and measure crop’s nutrient content, pest and
pathogens, weeds, moisture level and fertility of soil and
others to increase crop yield. The large surface-to-volume
ratio and high reactivity of TiO 2 -NPs considered suitable as
delivery agents for different molecules, proteins, nucleotides
and other chemicals in plants that may help in crop
improvement. They can be used as a carrier of agrochemicals and facilitate site targeted, controlled and slow release
of nutrients for better growth and high yield.
4.2 TiO 2 Nanoparticles and Crop Protection
Owing to their photo-protective and photocatalytic characteristics, TiO 2 -NPs are known to have potential application
in different formulations in plant protection as they amend
the life span of chemically active ingredients present in
plants (Gogos et al. 2012; Khot et al. 2012). Under biotic
stress, various pests and pathogens involved which infect a
wide species of crop plants and cause a huge crop loss with
reduced quantity and quality of plant products. Many
chemicals as pesticides, bactericides, fungicides are being
used to manage these phyto-pathogens in agriculture to get
better crop yield and efficiency. But they are highly toxic and
cause various human diseases and environmental threats.
Thus, there is an urgent need to find some green alternatives
that can effectively control pests and pathogens resistant to
chemicals/pesticides, in an environmentally friendly manner.
Therefore, NP-mediated green pesticides are now become of
unusual significance in crop protection (Chowdappa and
62
R. Singh et al.
influence their metabolic activities, plant growth and
development. Besides this, they can also alter soil properties like physico-chemical and biological which can
improve soil health and its quality. So, they can be used
as nanofertilizers and nanosensors.
• Protecting agents: TiO 2 -NPs are found to be effectively
used in plant protection against various stresses like cold
stress, drought, salinity stress, heavy metal toxicity and
others. Also, due to their unique properties and chemical
activities they can be utilized for crop protection from
pests and pathogens. So, they can be utilized as bactericides, nanoherbicides and nanopesticides.
For the achievement of above-mentioned benefits, TiO 2 -
NPs are used as carrier agents for smart targeted delivery of
various nutrients and biological molecules which is supposed to get indulged within soil and plant. The detailed
discussion and studies to support the utilization of TiO 2 -NPs
in order to promote agriculture production are given in the
following sections (Table 3).
4.1 Nanoparticles as Growth Promoter
With an objective to promote TiO 2 -NPs use for agricultural
applications, their effects in seed germination as well as in
seedling growth have been investigated in several crop
plants (Tables 2 and 3A) and found contradictory (i.e., both
positive and negative results). There is no agreement on the
responses of plants to TiO 2 -NPs exposure because different
plant species, their growth stages and treatment conditions
seem to display diverse responses (Cox et al. 2016;
Mukherjee et al. 2016; Mattiello et al. 2015; Tan et al. 2018;
Chaudhary and Singh 2020).
TiO 2 –NPs have been reported to promote crop yield by
improving seed germination, growth and development of
wide varieties of plants, viz. Cicer sp., cabbage, Brassica
napus, cucumber, spinach, onion, soybean, maize, tomato,
wheat and many more. Entry of NPs into the seeds plays a
critical significant role in increasing the rate of seed germination (Fan et al. 2016). The priming of seeds with TiO 2 –NPs
could promote seed germination and plant growth by
increasing chlorophyll contents, photosynthesis performance
by improving light absorbance, activate the photochemical
reaction, induction of rubisco activase and nitrate reductase
activity and water conduction (Zheng et al. 2005; Raliya et al.
2015a; Singh et al. 2016). Studies have reported that exposure
to definite doses of TiO 2 -NPs accelerated germination in aged
seeds of spinach and the germination time in Triticum aestivum seeds (Zheng et al. 2005; Feizi et al. 2012; Jiang et al.
2017). Size of NPs plays a very important role in its behavior,
toxicity and reactivity. A treatment of TiO 2 -NPs (*20 nm) to
Canola seeds, improved seed germination and seedling vigor
at 2000 mg l
−1 concentration (Mahmoodzadeh et al. 2013).
Lu et al. (2006) reported an improvement in seed germination
and growth at low concentrations of mixture of TiO 2 -NPs and
nSiO 2.
By virtue of their photocatalytic properties, TiO 2 -NPs
induce oxidation–reduction reactions and increase growth
and development of plant (Hong et al. 2005; Lei et al. 2008;
Li et al. 2015). Besides, photo-attenuation activity of TiO 2 -
NPs protects the chloroplasts from photo-oxidation and
aging and hence, extends the photosynthetic activity of
chloroplasts (Yang et al. 2008). Overall, seed priming and
application of TiO 2 -NPs via roots or leaves (soil amendment
or foliar spray) at low concentrations could be a better
alternative to improve the quality, biomass and yields of
many cultivars (Moaveni et al. 2011; Morteza et al. 2013;
Raliya et al. 2015a, b; Rafique et al. 2018). Du et al. (2011)
had demonstrated that the concentrations of TiO 2 -NPs significantly affect the enzymatic activities of soil enzymes
which in turn affect the soil properties and health. Therefore,
TiO 2 -NP can be utilized as nanofertilizers to improve agriculture output.
Besides, they have a potential to be used as nanosensors
to detect and measure crop’s nutrient content, pest and
pathogens, weeds, moisture level and fertility of soil and
others to increase crop yield. The large surface-to-volume
ratio and high reactivity of TiO 2 -NPs considered suitable as
delivery agents for different molecules, proteins, nucleotides
and other chemicals in plants that may help in crop
improvement. They can be used as a carrier of agrochemicals and facilitate site targeted, controlled and slow release
of nutrients for better growth and high yield.
4.2 TiO 2 Nanoparticles and Crop Protection
Owing to their photo-protective and photocatalytic characteristics, TiO 2 -NPs are known to have potential application
in different formulations in plant protection as they amend
the life span of chemically active ingredients present in
plants (Gogos et al. 2012; Khot et al. 2012). Under biotic
stress, various pests and pathogens involved which infect a
wide species of crop plants and cause a huge crop loss with
reduced quantity and quality of plant products. Many
chemicals as pesticides, bactericides, fungicides are being
used to manage these phyto-pathogens in agriculture to get
better crop yield and efficiency. But they are highly toxic and
cause various human diseases and environmental threats.
Thus, there is an urgent need to find some green alternatives
that can effectively control pests and pathogens resistant to
chemicals/pesticides, in an environmentally friendly manner.
Therefore, NP-mediated green pesticides are now become of
unusual significance in crop protection (Chowdappa and
62
R. Singh et al.