The increased projection of population growth has questioned on the global food demand as it need to be doubled by 2050. But the sudden arrival of biotic and abiotic stress has disrupted the food production cycle which can be alarming in future days
(Tilman et al., 2011). The use of agrochemicals to get rid of biotic stresses are another challenging factor in sustainable agriculture system as they have toxic residual effect in environment as well as in food chain. A novel emerging and innovative method, nanotechnology was discovered about a half century ago for industrial application only, which afterwards attracted many researchers and crop scientist to implement this technique in an ecofriendly way to develop a green and sustainable agriculture strategy
(Mukhopadhya and Sharma, 2013). With its wider and potential application in Agricultural sciences, it has become one of the promising approaches to target a broad range of pests (Ul
Haq et al., 2020). This technology includes a combination of methods and techniques to convert a material in to an ultramolecular level which is more reactive and potential. Application of chemicals is not suitable in sustainable agriculture due to its low-impact compounds and toxic residues in environment. The use of nanotechnology in agriculture aims to decrease the use of agrochemicals and to increase the nutrient uptake through nano-based fertilizers
(El-Ghamry et al., 2018). These nanoparticles show high permeability, stability and solubility. Role of nanoparticles on growth of some selected cereals were checked by Jyothi and Hebsur in 2017.
Nanoparticles (NP) are a minimum of 100 nm in size and made up of gold, silver, silicon, copper, titanium dioxide, zinc oxide and carbon. Due to large surface area to volume ratio and small size, they can absorb, react and carry compounds like DNA, RNA, proteins or small molecular drugs with high efficiency. They offer more advantages than agrochemicals by reducing toxic substances, increasing shelf life and improving solubility
(Worrall et al., 2018). These nanoparticles have the potential to work more effectively when directly applied to any plant parts such as roots, seeds, foliage
etc. Two key mechanisms present behind the nanotechnology-based plant protection. Firstly, it can be directly applied as to protect crop and secondly, they act as carrier for the existing chemicals for effective delivery at target sites. The methods for synthesis of nanoparticles are quite diverse whereas the green nanoparticle synthesis is easy, rapid and conducted in ambient pressure and temperature. Without any doubt, more in depth research on agricultural nanotechnology surely leads towards new generation pesticides in upcoming days. In this review, we have discussed the potential effect and function of different nanoparticles on various plant pathogens.
Potential effect of NPs against phytopathogens
In recent years, plants are mostly affected by many biotic agents which can cause a yield loss of up to 100%. Previous studies have shown that 20 to 40% yield loss was observed per year and 10% is only in fruit crops
(Pattanayak and Das, 2020) .Nanoparticles are one of the new frontiers of sustainable agriculture. The direct effect of several nanoparticles has proved its potentiality against a wide range of plant pathogenic micro-organisms and insects through different approaches (Fig 1 and Table 1). The tremendous prospects of nanoparticles in monitoring and managing the pathogens can advance the existing and future agriculture by increasing the growth curve vertically.
Effect of silver NPs on phytopathogens
The potentiality of NPs has been examined in laboratory conditions as well as in open field conditions in different experiments. Several NPs have proved its effectiveness in suppressing a wide range of plant pathogens. Silver NPs are getting popular due to its “green synthesis” mechanism in plant pathogens
(Das and Pattanayak 2020). In 2007, Kim and his coworkers tested the three different types of silver nanoparticles against plant pathogenic fungi like
Fusarium oxysporum f.
sp.
cucumerinum,
Fusarium oxysporum f.
sp.
lycopersici,
Fusarium solanum,
Pythium aphanidernatum,
Alternaria alternata,
Alternaria brassicola,
Cladosporium cucumerinum etc in vitro and proved the inhibitory effect of silver NPs against the above pathogens. Many plant pathogenic bacteria and fungi such as
Magnaporthe grisea and
Bipolaris sorokiniana can also be suppressed significantly with the application of silver NPs
(Jo et al., 2009). Similarly, in another experiment, highest inhibitory effect was observed in case of
Proteus vulgaris,
Escherichia coli and
lowest in staphylococcus aureus.
Effect of zinc NPs on phytopathogens
Several zinc-based NPs are proved as one of the effective control measures against plant pathogenic fungi and bacteria. Antifungal activity has been observed in many zinc NPs against
Botrytis cinerea,
Penicillium expansum at 12 mmol L-1
(He et al., 2018). Growth and morphological changes such as hyphae thinning, modification in clumping tendency
etc, have been observed due to zinc NPs at 9mmol L-1 concentration
(Arciniegas-grijalba et al., 2017). Similarly, zinc NPs directly affect the colonization behavior of many bacteria
viz.
Proteus aeruginosa in vitro (Jayaseelan et al., 2012). Characteristics of zinc NPs such as size and concentration are directly proportional to the effectiveness of NPs. It was observed that decrease in particle size of NPs resulted in increased antibacterial effect against
Escherichia coli and
Staphylococcus aureus.
Effect of Copper NPs on phytopathogens
Several copper formulated NPs are available commercially which are used to protect the plants against fungi. Copper based fungicides are playing a major role in plant disease management from early periods. These NPs mainly affect the DNA, protein and lipids resulting in suppression of the pathogenic fungi. An
in vitro study has shown the inhibitory effect against several fungi like
Alternaria alternata,
Phoma destructive,
Curvularia lunata and Fusarium oxysporum (Kanhed et al. 2013). A potential nanometallic fungicide was prepared by using high concentration of copper NPs in biological reduction method which proved its effectiveness against red root rot of tea. A mixture of Copper NPs with soda lime glass powder has tested against bacteria which proved its antibacterial effect against various gram positive and gram-negative bacteria. Pomegranate blight caused by
Xanthomonas axonopodis pv.
punicae can be controlled by the application of copper NPs
(Mondal and Mani, 2012).
Influence of NPs as growth promoters in plants
Use of nanoparticles as a growth promoter is one of the new and novel techniques in agriculture. The NPs can play the role of biofertilizer to enhance the plant growth by supplying proper nutrients or making them available to the plant system. This ecofriendly approach has increased its popularity due to its sustainable characters such as high reactivity, higher bioactivity, surface effects
etc. Nano biofertilizers are mostly used in farming to improve the nutrient efficiency. These are the modified form of synthetic fertilizers which help to improve the soil fertility, quality as well as enhance the quality of plant system by adding proteins, carbohydrates
etc.
Nano fertilizers are mainly available in three types such as nanoscale fertilizer, nanoscale coating and nanoscale additives. These nano fertilizers can alter the seed vigor, increase chlorophyll formation to increase the photosynthesis rate which positively impacts the plant growth.
Tarafdar et al., (2012) have observed the increase in availability and uptake of nutrients after foliar application of encapsulated nano fertilizers. Foliar application of zeolite-based nanoparticles can prevent the loss of nutrients through denitrification, leaching loss, volatilization or any other methods. Some nano fertilizers negatively impact the growth of plant by affecting the seedling growth and germination.
