Nanotechnological Interventions in Agriculture

3 Plant Biotechnology Section, Department of Botany, Aligarh Muslim University, Aligarh 202002, India; moc.liamg@meezaahabas (S.T.); moc.liamg@79isawalda (A.W.); moc.liamg@103rihsabnafri (I.B.G.); ni.ca.uma@tb.dazhahsa (A.S.)

Adla Wasi

3 Plant Biotechnology Section, Department of Botany, Aligarh Muslim University, Aligarh 202002, India; moc.liamg@meezaahabas (S.T.); moc.liamg@79isawalda (A.W.); moc.liamg@103rihsabnafri (I.B.G.); ni.ca.uma@tb.dazhahsa (A.S.)

Irfan Bashir Ganie

3 Plant Biotechnology Section, Department of Botany, Aligarh Muslim University, Aligarh 202002, India; moc.liamg@meezaahabas (S.T.); moc.liamg@79isawalda (A.W.); moc.liamg@103rihsabnafri (I.B.G.); ni.ca.uma@tb.dazhahsa (A.S.)

Anwar Shahzad

3 Plant Biotechnology Section, Department of Botany, Aligarh Muslim University, Aligarh 202002, India; moc.liamg@meezaahabas (S.T.); moc.liamg@79isawalda (A.W.); moc.liamg@103rihsabnafri (I.B.G.); ni.ca.uma@tb.dazhahsa (A.S.)

Abolghassem Emamverdian

1 Co-Innovation Centre for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, China; nc.ude.ufjn@nayidrevmame (A.E.); nc.ude.ufjn@ykmar (M.R.)

2 Bamboo Research Institute, Nanjing Forestry University, Nanjing 210037, China

Muthusamy Ramakrishnan

1 Co-Innovation Centre for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, China; nc.ude.ufjn@nayidrevmame (A.E.); nc.ude.ufjn@ykmar (M.R.)

2 Bamboo Research Institute, Nanjing Forestry University, Nanjing 210037, China

Yulong Ding

1 Co-Innovation Centre for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, China; nc.ude.ufjn@nayidrevmame (A.E.); nc.ude.ufjn@ykmar (M.R.)

2 Bamboo Research Institute, Nanjing Forestry University, Nanjing 210037, China

1 Co-Innovation Centre for Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing 210037, China; nc.ude.ufjn@nayidrevmame (A.E.); nc.ude.ufjn@ykmar (M.R.)

3 Plant Biotechnology Section, Department of Botany, Aligarh Muslim University, Aligarh 202002, India; moc.liamg@meezaahabas (S.T.); moc.liamg@79isawalda (A.W.); moc.liamg@103rihsabnafri (I.B.G.); ni.ca.uma@tb.dazhahsa (A.S.)

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

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Abstract

Agriculture is an important sector that plays an important role in providing food to both humans and animals. In addition, this sector plays an important role in the world economy. Changes in climatic conditions and biotic and abiotic stresses cause significant damage to agricultural production around the world. Therefore, the development of sustainable agricultural techniques is becoming increasingly important keeping in view the growing population and its demands. Nanotechnology provides important tools to different industrial sectors, and nowadays, the use of nanotechnology is focused on achieving a sustainable agricultural system. Great attention has been given to the development and optimization of nanomaterials and their application in the agriculture sector to improve plant growth and development, plant health and protection and overall performance in terms of morphological and physiological activities. The present communication provides up-to-date information on nanotechnological interventions in the agriculture sector. The present review deals with nanoparticles, their types and the role of nanotechnology in plant growth, development, pathogen detection and crop protection, its role in the delivery of genetic material, plant growth regulators and agrochemicals and its role in genetic engineering. Moreover, the role of nanotechnology in stress management is also discussed. Our aim in this review is to aid researchers to learn quickly how to use plant nanotechnology for improving agricultural production.

1. Introduction

Agriculture is one of the most promising sectors to play in the world economy as it provides food for humans and animals and produces raw materials for various industries. For decades, the demographic data of the world population has been constantly changing, and the number of people is expected to exceed 9.7 billion by 2050 [1]. Moreover, according to the estimation of the Food and Agriculture Organization [2], the agriculture sector needs to produce twice as much food to meet the global demands by 2050. The increasing world population, decreasing cultivable land, high rate of deforestation and changing climatic conditions, especially increasing temperature and CO₂ levels, stress the need to develop new technologies to enhance the yield and productivity of plants during challenging environmental conditions. The challenges of abiotic stress on plant development and growth are among the emerging ecological impacts of climatic change [3]. Plants are fixed and hence exposed to extreme environmental situations such as drought, heavy metals, light intensities, UV, flood, etc., and these stressors from the environment can cause various stress to a variety of species [4,5]. These stressful conditions induce reactive oxygen species (ROS) which in turn cause degradation of the membrane, increase cell toxicity and retard plant growth. Meanwhile, antioxidant systems through enzymatic and non-enzymatic methods remove ROS and relieve stress produced due to oxidation.

However, in field conditions, distinctive effects on plants frequently take place due to this combination of stresses leading to unanticipated physiological effects [6]. Nowadays, various methodologies have been explored focusing on stress tolerance in plants. An effort has been made to breed crops with stress-tolerant traits in the past few decades by considering two important approaches, viz., conventional and mutation breeding. However, the uncertainty of results and the time-consuming process were the drawbacks of these two processes [7]. Introduction of exogenous genes or changing the expression level to improve stress tolerance and obtaining a genetically modified plant is another method [7]. However, this practice is limited and unacceptable in many countries leading to the limitation of this technique. Priming is another approach to make the plants resistant to environmental stresses. Chemical priming is helpful in the establishment of resistance because it induces the existing defense mechanism of the plant without resorting to genetic changes. Pre-treating or priming plants with natural or synthetic compounds enhanced response under stresses such as heat, salinity, drought, etc., in comparison to unprimed plants [8]. The defense mechanism of plants is enhanced by priming due to its ability to activate and amplify those signals which can control the accretion of ROS, redox signaling and expressions of the genes involved in resisting stresses [9]. Most frequently utilized priming agents are amino acids, polyamines, melatonin fungicides, phytohormones, reactive nitrogen, sulfur and oxygen species, etc. [10,11,12].

Today, the application of nanotechnology and its tools in the chemical priming field improved the effectiveness of the chemicals used for priming and thus reduced the chemical release into the environment [13]. Nanotechnology is a novel and innovative approach to develop and design real-world applications of materials at the nanoscale [14,15]. In the agricultural sector, nanotechnology has a great role in dealing with various issues such as making crop plants more resistant to biotic and abiotic stresses and increasing the productivity of the plants. In addition to this, problems associated with the overuse of fertilizers and pesticides and their harmful impact in relation to the environment could also be tackled with a targeted and proper use of nanotechnology [16,17]. Gradually, the nanotechnological intervention in agricultural sectors is increasing and making this sector an income-generating business [18]. Overall, the use of nanotechnology will enhance food quality and global production in an environmentally friendly way by solving the problem associated with water and soil [19,20].

Furthermore, NPs participate in growth and development and also provide protection to the plants. During stress responses, NPs can also modify and change the expression of the genes that cause biosynthesis and organization of cells, electrons and transport of energy [21]. The diverse physicochemical characteristics of nanoparticles is due to their smaller size. They are known for higher reactivity, biochemical activity and solubility due to a higher surface-to-volume ratio [22]. The target-specific and low-quantity release of NPs make them different from various other elements used in plants [23] In addition, the behavior of NPs depends strongly on their chemical composition, particle size and function. Moreover, NPs play a significant role in protecting the plant against different stressors, accelerating the scavenging of ROS, protecting photosynthetic machinery and reducing osmotic and oxidative stress [24,25,26]. Different types of NPs with their unlimited potential to revolutionize the agricultural sector have been used these days along with their benefits and drawbacks [19,27]. From various studies, it was established that nanoparticles are crucial for crop improvement, but their actual working mechanism and mode of interaction are still at an initial stage [28,29].

Nanomaterials (NMs) have become an elemental part of NPs due to their distinctive characteristics in terms of physical, chemical, mechanical and thermal properties. The NMs can be natural or tailored by using physical, chemical or biological methods [30]. In terms of the recent progress, an emphasis has been placed on the use of nanomaterials (NMs) or engineered nanoparticles (ENPs) in agriculture sectors. Nowadays, engineered NPs are used as nanoherbicides and nanopesticides by considering two important factors: controlling the release of agrochemicals with minimized nutrient loss and enhancing plant morphogenesis by targeting particular cellular organs of plants. These days, nanomaterials are present in different aspects of day-to-day life, such as the environment, agriculture, food and cosmetic industry, waste water treatment, medicine, energy information and communication [31,32,33,34,35]. Various NMs such as single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), silver, silicon, zinc, iron and titanium dioxide (TiO₂) have been observed to improve plant growth and development [19,27,36]. Therefore, NPs are involved in different aspects of agriculture such as making the plant resistant to disease and pests, improving nutrient absorption, acting as a carrier for various vital compounds and improving the effectiveness of fungicides, pesticides, herbicides and the delivery of fertilizers leading to a boosted growth of plants [27,37]. However, the use of NMs for the improvement of the crop and sustainable agriculture is still in its initial phase. Hence, to address the problems in agriculture, the knowledge of NPs and their application in agriculture is crucial for workers. It is also mandatory to build up a fundamental understanding of NPs in relation to agriculture. This section briefly describes the role of nanotechnology in different aspects. Considering the importance of nanotechnology, the aim of this review is to summarize the available information and developments on nanotechnological interventions in agriculture. Furthermore, the current communication relates to the use of tailored NMs for sustainable agriculture with a special emphasis on handling plant stress.

2. Nanoparticles: Scientific Aspects

The term “nano” is derived from a Greek word that means “dwarf”, and it signifies 10 −9 parts of any unit [38]. It can be organic or inorganic molecules having dimensions of less than 100 nm and a wide surface area [39]. Plants react differently in the presence of different NPs depending on the size, shape and chemical and physical properties of the NPs [40]. Figure 1 describes the different types of NPs based on function, morphology, chemical structure and physiochemical properties. Applied NPs in agriculture are categorized into three groups, i.e., organic, inorganic (metal and metal oxide NPs) and combined NPs [27]. In most studies, inorganic NPs are used, i.e., metal 25% and metal oxides 54%, while carbon-based NPs are used in only 10% of studies; ZnO, TiO₂, CuO and CeO₂ are the most commonly utilized metal oxide NPs, whereas Ag NPs are most commonly used in the metallic NP group [41]. Various other distinctive forms of NPs are core-shell NPs, polymer-coated magnetite NPs, photochromic polymer NPs, Au NPs, Pd NPs and Ni NPs, while some other NPs are metal oxides, for example, MgO NPs, TiO₂ NPs, CeO₂ NPs, ZrO₂ NPs and ZnO NPs. All these NPs have a specific set of properties and can be synthesized by conventional or unconventional approaches [42]. Generally, two processes (top down and bottom up) are employed for the synthesis of NPs [43,44] ( Figure 2 ). Different lithographic techniques, for example, milling, grinding, etc., are employed to break down bulk material into substances at the nanoscale in top-down approaches. While in the case of bottom-up approaches, atoms self-assemble into new nuclei and eventually grow into particles with a nanoscale that also includes physical and chemical methods. Toxic starting materials, high running costs, toxic contamination and high temperature are required in these methods to obtain the final products [43,44]. Several attempts have also been performed to use biological catalysts, viz., plants, bacteria, fungi and yeast, in order to avoid obstacles found in physical and chemical methods [45].