ReviewEmerging technology applications for improving seed germination
Introduction
World food grain production rate was about 2547.1 million metric tons, while the consumption reached even higher in accordance with the report of United Nations Food and Agriculture Organization (FAO), in the year 2016. This has created fears on whether our agricultural lands will be able to feed its population in short term. Whereas in long term, it has been anticipated that the world needs to increase its production further, to feed a population of 9 billion by 2050. Therefore, food security has become an important alarming issue across the globe. With the fast development of urbanization and industrialization, the dominant way to secure food safety is by improving yield of grain and germination along with the quality of crops in outlook of the actuality that cultivatable lands are hard to increase (Edmondson, Davies, Gaston, & Leake, 2014) and the natural resources are depleting at a rapid rate.
The seed has the major independent structure, responsible for next generation of plants, maintaining the germplasm, improving species diversity and production capacity (Sharififar, Nazari, & Asghari, 2015). By definition, germination involves those processes which initiate with the uptake of water by the inactive dry seed and conclude with the development of the embryonic axis (Bewley & Black, 1994). Hence, seed germination is a very important stage of plant life and is influenced by both intrinsic and extrinsic factors. The most important factors for germination include water, temperature, oxygen, and light (Raven, Evert, & Eichhorn, 2005, p. 639). During favorable condition seed germination and seed establishment takes place quickly. Whereas, during extreme condition an intrinsic block to germination exists called, dormancy; is a mechanism that slows down germination during unsuitable ecological condition, when the chance of sustenance of seedling is very short (Bewley, Black, & Halmer, 2006). Hence, for the seed to start the action of germination the state of dormancy has to be shaken. The simplest method employed to demolish the dormancy is controlling the salinity, humidity, and temperature of the environment in which seeds are kept initially (Baskin & Baskin, 1998). But in this method, though germination takes well at the initial stage when the nursery seedlings are transferred to actual field condition they showed a reduced growth rate. Another method applied to overcome the period of dormancy is the alteration of plant hormones like abscisic acid and gibberellic acid artificially, by inducing some other hormone (Sozzi & Chiesa, 1995). Seed stratification and scarification are employed to remove the dormancy period and hence improved the germination. Irrigation is also a significant parameter that controls the level of germination. But in the current scenario, since water is a scarce resource, the availability of water to the required levels in fields along with the quality of water used is a matter of concern. The most common method used to enhance germination is through the use of fertilizers or pesticides (Ramteke, Narwade, Gurav, Chavan, & Wandre, 2013). It was observed that common fertilizers like phosphate, diammonium, urea, and many other pesticides were used to increase seed germination yield. Though the fertilizer application increased the yield to a great extent their adverse effects on the environment and living organisms remain a major concern.
The germination power and growth yield of agricultural seeds are enhanced by application of chemical and physical methods that lead to structural damage, genetic dissimilarity in seeds to great extent and cause negative effects to life and nature. An effort has been taken up by the research community to check the impact of the application of some novel technologies on seed germination and growth rate (Harris et al., 2001). The novel technologies discussed in this review paper has been used in many mass transfer processes such as in gelation, extraction, and coagulation etc. However, in recent years, these technologies have also broadly been applied as an efficient technique for breaking dormancy and improving the germination characteristics of seeds. Hence, the application of these novel technologies will represent a good score for improving the yield of agricultural production. These emerging techniques offer several other advantages over time-honored chemical and physical treatments. First, the amount of pesticides is reduced, thus decreasing negative impact on the environment and living organisms. Second, the very low genetic deviation is caused in seeds. Another benefit is that these novel techniques can also be employed on seed even during storage, for disinfection prior to sowing (Joshi, Mahendran, Alagusundaram, Norton, & Tiwari, 2013).
The main objective of this review paper is to summarize the contribution of novel technologies namely: high pressure processing, pulsed electric field, ultrasound, ozone processing, ultraviolet, magnetic field, microwave radiation, non-thermal plasma, electrolyzed oxidizing water, and plasma activated water on germination rate, growth rate, growth characteristics and yield of seed. The reasons for the positive and negative impact of these technologies and their mechanism of action on seeds are presented in Fig. 1.
Section snippets
High pressure processing (HPP)
High pressure processing is one of the food processing technology which improves quality and safety of food at both solid and liquid condition. It is carried out at ambient temperature and at very high pressures of range 300–800 MPa for about 3–5 min, using a transmitting fluid (typically water). HPP in food application is governed by two relevant scientific laws. The first is Le Chatelier's principle, which states that as the pressure of a system in equilibrium is altered it tends to come back
Pulsed electric field processing (PEF)
PEF treatment involves the process of exposing the food materials sandwiched among two electrodes to short pulses (μs) at very high voltages (kV/cm). In common, the treatment systems of PEF consist of treatment chamber, fluid handling system, pulse generator, and monitoring system (Zhang, Barbosa-Cánovas, & Swanson, 1995). When the electric field is employed for few microseconds it changes the basic cell structure and breaks down the membrane of the cell. This process is known as
Ultrasound (US)
The term “ultrasound” describes to the pressure waves of frequencies over the range 20 kHz. The power ultrasound used in food treatment comprises sound waves of frequencies ranging from 20 to 100 kHz and sound intensity of 10–1000 W/cm2 (Piyasena, Mohareb, & McKellar, 2003). The use of these pressure waves is often combined with added parameters like temperature, pressure and chemical treatment at moderate intensities (Raso, Palop, Pagan, & Condón, 1998). During the process of sonication, sound
Ozone processing
Ozone (O3) is a molecule that exists in gaseous state and is produced from the oxygen molecule due to the combined effect of ultraviolet rays and electric discharges in the atmosphere. It possesses a half-life of about 12 h in the gaseous phase and 20–25 min in aqueous form and hence is highly unstable. This instability causes the ozone gas to decompose violently at a very high temperature (Streng, 1961). Hence low concentration of ozone is used at commercial scale. Ozone being a powerful
UV light
Ultraviolet (UV) is an electromagnetic light radiation which is generated from the sun or light source and is imperceptible to the human eye. UV light falls between the wavelength of range 100–400 nm. It is further subcategorized into four bands: UV-A from 315 to 400 nm; UV-B from 280 to 315 nm; UV-C from 200 to 280 nm and the vacuum UV from 100 to 200 nm. The UV light is studied to have a broad application in the food industry. It has wide antimicrobial action with the power to inactivate
Magnetic field
The area around a magnet, where the force that is capable of magnetizing surrounding body exist is called a magnetic field. It exists around electric current, varying electric fields, and magnetic dipoles. It was when a U.S. patent was granted to Hofmann, the first proposal of use of magnetic force lines in food preservation as a non-thermal technology was introduced (Hofmann, 1985). Seed germination was affected by two levels of field lines namely electromagnetic field exerted by the
Microwave radiation
Microwaves are electromagnetic energy has a frequency range from 300 to 300,000 MHz and falls between infrared and radio waves. Microwave (MW) radiation has very small energies that are insufficient to ionize atoms, hence they are also called non-ionizing radiations (Piyasena, Dussault et al., 2003). When MW radiation penetrates through a material, part of the energy is transmitted, part is reflected, and the remaining is absorbed by the material. The interaction of the electric field component
Non-thermal plasma (NTP)
Plasma is a high energy state and comprises of negative and positive ions, electrons, neutral molecules, with the concentrations of each balanced making plasma as neutral overall (Misra, Tiwari, Raghavarao, & Cullen, 2011). The types of plasma generated are thermal and non-thermal plasma (NTP) based on the mean temperatures of their heavy particles like ions and neutral species. In the thermal plasma, all the particles are in thermodynamic equilibrium, while a significant difference in kinetic
Electrolyzed oxidising water (EOW)
Electrolyzed oxidizing water (EOW), also called as strongly acidic electrolyzed water (SAEW) was introduced in Japan. To produce EOW electricity is passed through a solution of dilute saltwater within which a membrane is placed to separate anode and cathode. The reaction at electrodes generates two products namely sodium hydroxide and hypochlorous acid (Joshi et al., 2013). The first kind is water formed from positive side (anode) called as EOW with pH (2.3–2.7), ORP greater than 1000 mV and
Plasma activated water (PAW)
Plasma is fourth and high energy phase of matter has found a broad application in agriculture and food industry since nineteenth century. However, during mid-twentieth century scientists revealed a new application in plasma technology; a new kind of water which is free of chemicals, salt and harmful processes called plasma activated water (PAW) were produced on exposing water to plasma. Water generated through plasma technology possessed to have a high value of pH and comprises of O radical, H
Conclusion
In this study, we reviewed and summarized the contribution of emerging technologies on various seed germination. The reasons for the positive and negative impact of these technologies and their mechanism of action on seeds are presented. Ultrasound, UV-A, UV-C and non-thermal plasma treatment were supported to be effective in enhancing seed germination where the surface modification of treated seeds have important causes whereas in the pulsed electric field and microwave treatment, the
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