Spraying of TiO 2 -NPs sol (average size of 30.6 nm) on
cucumber leaves controlled bacterial angular spot and
downy mildew diseases caused by Pseudomonas syringe pv
lachrymans and Xanthomonas vesicatoria because it form an
adhesive and thin transparent film like covering on the surface of leaf (Zhang et al. 2007). Siddiqui et al. (2019)
observed that application of 0.25 and 0.50 ml l
−1 of TiO 2 -
NPs to plants with, or without, bacterial strain had not only
improved the growth, photosynthetic pigment contents
(chlorophylls and carotenoids), antioxidative enzymes, proline and H 2 O 2 contents, but also increased resistance to
diseases like soft rot, bacterial pocket and leaf spot caused
by Pectobacterium betavasculorum, Xanthomonas campestris pv. Beticola (Pammel) and P. syringae pv. aptata in
beetroot. In the past few years, antimicrobial photocatalyst
technology has been developed. Following this, many photoactivated NP formulations of TiO 2 with Zn and Ag have
been developed and applied to manage bacterial leaf spot on
Rosa ‘Noare’ and tomato caused by Xanthomonas sp. (Paret
et al. 2012, 2013a, b).
Field applications of TiO 2 -NPs formulations significantly
reduced the survival of mentioned pathogens devoid of any
adverse impacts on plants growth. Similarly, Boxi et al.
(2016) reported Ag doped (hollow and solid) TiO 2 -NPs to be
effective against two strong plant pathogens, Fusarium
solani (wilt disease) and Venturia inaequalis (causes apple
scab disease) in presence of visible light that attributed to
oxidative damage to the cell membrane caused by
•
OH
radicals that are generated during photocatalysis, and by
reacting with sulfide and disulfide of cellular proteins (Lin
et al. 2011; Gupta et al. 2013). TiO 2 -NPs take part in catalytic oxidation reaction with oxygen and thiol (-SH) groups
that ultimately lead to cell death by creating blockage of
bacterial respiration. NPs also arrest the production of toxic
pigment that is called naphthoquinone for F. solani which
has a role in fungal pathogenicity (Boxi et al. 2016).
Moreover, a combination of TiO 2 , Al and SiO 2 was found to
be useful in managing downy and powdery mildew in grapes
(Bowen et al. 1992), probably due to their direct effects on
the fungal hyphae, intervention with detection of plant surface and activation of plant antioxidant defense system.
Besides, visible light-activated TiO 2 -NPs co-doped with
nitrogen and fluorine was observed to be effective against F.
oxysporum and could be used as antifungal agents
(Mukherjee et al. 2020).
Shaker et al. (2017) found TiO 2 -NPs as an efficient larvicidal agent against the larvae of cotton leaf worm (Spodoptera littoralis). TiO 2 -NPs also affected some biological
parameters (larval period, pupation, adult emergence, productiveness, hatching of eggs, adult longevity and sex ratio)
of this insect where it caused irregularities in larvae, pupae
and adult stages. TiO 2 -NPs’ application may reduce the
problems caused by S. littoralis of the host crops and
improve yield. Goswami et al. (2010) reported the effects of
Al 2 O 3 , ZnO, TiO 2 and Ag NPs against pest and pathogens.
Al-Bartya and Hamzab (2015) that biosynthesized-TiO 2 -
NPs also were lethal to the larvae of red palm weevil
Rhynchophorus ferrugineus. As they are biosynthesized and
novel with respect to their surface coating and reactivity,
they may be an effective alternative to control
pesticide-resistant pests.
4.3 TiO 2 Nanoparticles and Plants Tolerance
Under Various Stresses
Environmental pollution and climate change directly or
indirectly affects the growth and development of plants
which in turn reduce crop productivity by imposing various
stresses on crop plants. Thus, it is essential to pave ways to
ameliorate the negative effects of different stresses to obtain
optimum yields. In recent years, TiO 2 -NPs are emerging as
potential source for plant improving plant performance
under various abiotic stresses (Frazier et al. 2014). Some
studies have been documented in Table 3C.
Studies observed that application of TiO 2 -NPs improves
plants growth and development by alleviating stress-induced
toxicity by enhancing antioxidants (Song et al. 2012;
Mohammadi et al. 2014). TiO 2 -NPs application alleviate
toxicity and increased tolerance against cold in chick pea
(Mohammadi et al. 2014), heat in tomato (Qi et al. 2013),
salinity in tomato and barley (Khan 2016; Karami and
Sepehri 2018; Gohari et al. 2020), drought in Triticum
aestivum, Linum usitatissimum (Jaberzadeh et al. 2013;
Aghdam et al. 2016; Mohammadi et al. 2016) and cadmium
toxicity in soybean and rice (Ji et al. 2017; Singh and Lee
2016). Exogenous application of anatase-TiO 2 -NPs not only
ameliorates the damage to flax seed plant under drought
stress but also improves its drought stress tolerance by
improving morphological and physiological traits (Aghdam
et al. 2016; Mohammadi et al. 2016). An enhanced chlorophyll and carotenoids contents, and low levels of H 2 O 2 and
MDA were noticed in plants treated with low concentration
(10 mg l
−1 ) of TiO 2 -NPs, while an improved value of seed
oil and protein contents were reported in plants treated with
higher concentration of TiO 2 -NPs (100 mg l
−1 ). Likewise,
in another study, Faraji and Sepehri (2019) observed that the
exposure of TiO 2 -NPs to wheat plant increased its seed
germination and early growth of seedling under polyethylene glycol (PEG)-stimulated drought stress via counteracting the adverse effects of drought on seed germination,
seed vigor, root and shoot length and fresh weight of seedling. In addition, TiO 2 -NPs application in soil significantly
ameliorate tolerance against Cd stress in soybean and rice by
increasing chlorophyll, photosynthetic rate and growth
parameters; and regulating Cd accumulation (Ji et al. 2017;
66
R. Singh et al.
cucumber leaves controlled bacterial angular spot and
downy mildew diseases caused by Pseudomonas syringe pv
lachrymans and Xanthomonas vesicatoria because it form an
adhesive and thin transparent film like covering on the surface of leaf (Zhang et al. 2007). Siddiqui et al. (2019)
observed that application of 0.25 and 0.50 ml l
−1 of TiO 2 -
NPs to plants with, or without, bacterial strain had not only
improved the growth, photosynthetic pigment contents
(chlorophylls and carotenoids), antioxidative enzymes, proline and H 2 O 2 contents, but also increased resistance to
diseases like soft rot, bacterial pocket and leaf spot caused
by Pectobacterium betavasculorum, Xanthomonas campestris pv. Beticola (Pammel) and P. syringae pv. aptata in
beetroot. In the past few years, antimicrobial photocatalyst
technology has been developed. Following this, many photoactivated NP formulations of TiO 2 with Zn and Ag have
been developed and applied to manage bacterial leaf spot on
Rosa ‘Noare’ and tomato caused by Xanthomonas sp. (Paret
et al. 2012, 2013a, b).
Field applications of TiO 2 -NPs formulations significantly
reduced the survival of mentioned pathogens devoid of any
adverse impacts on plants growth. Similarly, Boxi et al.
(2016) reported Ag doped (hollow and solid) TiO 2 -NPs to be
effective against two strong plant pathogens, Fusarium
solani (wilt disease) and Venturia inaequalis (causes apple
scab disease) in presence of visible light that attributed to
oxidative damage to the cell membrane caused by
•
OH
radicals that are generated during photocatalysis, and by
reacting with sulfide and disulfide of cellular proteins (Lin
et al. 2011; Gupta et al. 2013). TiO 2 -NPs take part in catalytic oxidation reaction with oxygen and thiol (-SH) groups
that ultimately lead to cell death by creating blockage of
bacterial respiration. NPs also arrest the production of toxic
pigment that is called naphthoquinone for F. solani which
has a role in fungal pathogenicity (Boxi et al. 2016).
Moreover, a combination of TiO 2 , Al and SiO 2 was found to
be useful in managing downy and powdery mildew in grapes
(Bowen et al. 1992), probably due to their direct effects on
the fungal hyphae, intervention with detection of plant surface and activation of plant antioxidant defense system.
Besides, visible light-activated TiO 2 -NPs co-doped with
nitrogen and fluorine was observed to be effective against F.
oxysporum and could be used as antifungal agents
(Mukherjee et al. 2020).
Shaker et al. (2017) found TiO 2 -NPs as an efficient larvicidal agent against the larvae of cotton leaf worm (Spodoptera littoralis). TiO 2 -NPs also affected some biological
parameters (larval period, pupation, adult emergence, productiveness, hatching of eggs, adult longevity and sex ratio)
of this insect where it caused irregularities in larvae, pupae
and adult stages. TiO 2 -NPs’ application may reduce the
problems caused by S. littoralis of the host crops and
improve yield. Goswami et al. (2010) reported the effects of
Al 2 O 3 , ZnO, TiO 2 and Ag NPs against pest and pathogens.
Al-Bartya and Hamzab (2015) that biosynthesized-TiO 2 -
NPs also were lethal to the larvae of red palm weevil
Rhynchophorus ferrugineus. As they are biosynthesized and
novel with respect to their surface coating and reactivity,
they may be an effective alternative to control
pesticide-resistant pests.
4.3 TiO 2 Nanoparticles and Plants Tolerance
Under Various Stresses
Environmental pollution and climate change directly or
indirectly affects the growth and development of plants
which in turn reduce crop productivity by imposing various
stresses on crop plants. Thus, it is essential to pave ways to
ameliorate the negative effects of different stresses to obtain
optimum yields. In recent years, TiO 2 -NPs are emerging as
potential source for plant improving plant performance
under various abiotic stresses (Frazier et al. 2014). Some
studies have been documented in Table 3C.
Studies observed that application of TiO 2 -NPs improves
plants growth and development by alleviating stress-induced
toxicity by enhancing antioxidants (Song et al. 2012;
Mohammadi et al. 2014). TiO 2 -NPs application alleviate
toxicity and increased tolerance against cold in chick pea
(Mohammadi et al. 2014), heat in tomato (Qi et al. 2013),
salinity in tomato and barley (Khan 2016; Karami and
Sepehri 2018; Gohari et al. 2020), drought in Triticum
aestivum, Linum usitatissimum (Jaberzadeh et al. 2013;
Aghdam et al. 2016; Mohammadi et al. 2016) and cadmium
toxicity in soybean and rice (Ji et al. 2017; Singh and Lee
2016). Exogenous application of anatase-TiO 2 -NPs not only
ameliorates the damage to flax seed plant under drought
stress but also improves its drought stress tolerance by
improving morphological and physiological traits (Aghdam
et al. 2016; Mohammadi et al. 2016). An enhanced chlorophyll and carotenoids contents, and low levels of H 2 O 2 and
MDA were noticed in plants treated with low concentration
(10 mg l
−1 ) of TiO 2 -NPs, while an improved value of seed
oil and protein contents were reported in plants treated with
higher concentration of TiO 2 -NPs (100 mg l
−1 ). Likewise,
in another study, Faraji and Sepehri (2019) observed that the
exposure of TiO 2 -NPs to wheat plant increased its seed
germination and early growth of seedling under polyethylene glycol (PEG)-stimulated drought stress via counteracting the adverse effects of drought on seed germination,
seed vigor, root and shoot length and fresh weight of seedling. In addition, TiO 2 -NPs application in soil significantly
ameliorate tolerance against Cd stress in soybean and rice by
increasing chlorophyll, photosynthetic rate and growth
parameters; and regulating Cd accumulation (Ji et al. 2017;
66
R. Singh et al.