Review on the Effects of Seed Priming on Performance of Maize Seedlings

Maize ( Zea mays L.) is members of the grass family, Poaceae (Gramineae). It is believed that the crop was originated in Mexico. Maize is an important food crop in southeastern Ethiopian produced in a number of agro ecologies in region. The main objective of this senior seminar is to review the effect of seed priming on performance of maize seedling. The effect of Priming and ambient temperature due to different sowing dates on emergence of maize seedlings. Seed priming also called is osmo conditioning is one of the most promising treatments for reducing the time needed between sowing and seedling emergence. Seeds planted in early spring frequently experience low temperatures stress in soil during Germination and early plant growth. All part of the crop can be used for food and non-food products. In industrialized countries, maize is largely used as livestock feed and as a raw material for industrial products. .Different factors, such as soil moisture stress, temperature extremities, and soil salinity, poor seed bed preparation, weed competition, low seed quality, and extreme disease pressure adversely affect the emergence of maize seed. Seed priming could be used as a viable technology to improve seedling establishment. Rapid and uniform emergence has been achieved by seed priming in some field. Seed priming is an effective technology to enhance rapid and uniform emergence and to achieve high vigour, leading to better stand establishment and yield .There are several priming techniques, such as hydro priming osmo priming, halo priming, matrix priming and bio priming. Keywords : Seed physiological quality, Seed priming, Sowing date, Seedling emergence DOI: 10.7176/JBAH/10-14-05 Publication date: July 31 st 2020

human body cannot synthesize and has to be supplemented ( Krivanek et al,. 2007). Therefore adoption and cultivation of QPM with high concentration of lysine and tryptophan contents therefore could drastically reduce malnutrition, diseases and death among low income maize consumers in the developing countries (Mbuya et al., 2011).
Seed priming, a promising technique have been successfully employed to overcome the problem associated with poor germination and subsequent terratic crop stand under normal and stressful conditions (Jafar et al.,2012;). (Basra et al., 2011;Afzal et al., 2012) have e been tested to improve the maize performance under lown temperature stress. Kernel weight and composition can influence tolerance to cold stress, particularly in sweet corn, with heavier, kernels, containing higher starch, showing better germination ( Trimble et al , 2016 ).In the field, small kernels may have lower emergence under cold conditions (Frascaroli et al.,2013). . Seed priming can increase emergence rate, early seedling growth and stand establishment in many plant species (Khan. et al., 2010) Pre-sowing seed invigoration treatments have beneficial effect on field emergence, crop stand and seedling growth of Maize under low and sub-optimal temperatures (Rashid et al., 2002). Emergence performance of maize seeds varies with sowing dates due to variation in ambient temperature (Farooq et al., 2008) .According to Basu et al. (2005) found that primed seed sown at higher temperature showed higher emergence performance and dry matter compared to low temperature. Medany et al., (2007) stated that optimum temperature for maize growing is between 25 and 30 o C. The objective of this paper is to review the effect of maize seed priming on seedling performance of maize

LITERATUR EREVIEW 2.1. Origin and Botanical Description of the Maize
Origins and taxonomic organization of maize was hotly debated until the late 1970s after which genetic studies, including the use of molecular markers and comparative DNA sequence data allowed breakthroughs in the taxonomy and phylogeny of maize and its wild relatives, including the identification of specific loci involved in the domestication process (van Heerwaarden et al., 2011). Maize was domesticated in the tropical lowlands of southwest Mexico with subsequent introgression from teosinte (Piperno et al., 2009;Huford et al., 2013).
Maize diversified under genetic drift and selection as it was carried through a diverse habitats during its spread by humans both south and north from its origin, including its arrival in the southwestern region of North America by 2260 BC (Merrill et al., 2009). The initial selection for adaptation to a temperate environment then occurred during the subsequent 2000 yrs. in North America (Bouchet et al., 2013). Maize has become adapted to the broadest range of climatic conditions of all crops, from 40S in Chile to 50N in Canada and Russia, from sea level in the West Indies to elevations above 3400 m in the Andes (Bouchet et al., 2013). Maize is propagated by seed. Maize seed needs a soil that is warm moist well aerated and fine to give enough contact between the seed and the soil (Kassie et al., 2012).

Agro-Ecologies and Production of Maize in Ethiopia
The maize productivity gap between stressed and high potential areas is not only an issue of technology but also differences in climatic factors. Non-availability of suitable maize varieties is also responsible for such significant yield reduction (Mosisa et al., 2001).Unavailability of improved infrastructure and grain marketing represents major limiting factors for maize production. Wise utilization and conservation of natural resources will also have a significant impact on maize grain production (Mosisa et al., 2001).

Structure, Physiology and Breeding of Maize
The maize plant is often 2.5 m (meters) (8ft) in height, though some natural strains can grow 12 m (40 ft).The stem has the appearance of a bamboo cane and is commonly composed of 20 internodes of 18 cm (7 in) length. (Aorta, 2012) A leaf grows from each node, which is generally 9 cm (3.5 in)in width and 120 cm (4ft) in length (Arora .2012 ) Ears develop above a few of the leaves in the midsection of 18 cm. They are female inflorescences, tightly enveloped by several layers of ear leaves commonly called husks. Certain varieties of maize have been bred to produce many additional developed ears. These are the source of the baby corn used as a vegetable in Asian cuisine (Arora T. 2012). Most global production is provided by hybrid maize (Manuka et al., 2017a, b). Hybrids developed by CIMMYT yield >20% more than OPVs under optimal conditions, and the disparity is magnified to 30->60% under a biotic and biotic stress conditions (Masuka et al., 2017a). However, open-pollinated varieties (OPVs) provide the majority of seed supply in some regions provided by the formal breeding sector (e.g., West Africa), albeit with much regional variation (Kassie et al., 2012) and due to many cited issues including seed supply (Gafney et al., 2016). More resources in terms of breeding support over a longer period of time have been directed toward maize improvement in temperate climates than have been applied, to date, to the improvement in maize production in the tropics  and heterotic patterns are not firmly established in tropical maize populations ( Wen et al., 2011).

Seed Ageing and Salinity Induces Membrane Damage through Oxidative Stress
Biochemical and physiological deterioration during seed aging has been studied mostly under accelerated aging conditions using high temperatures and high seed water content. (Oliveira et al., 2011a;)Some studies indicate that membrane lipid per oxidation is one of the major causes of seed aging under accelerated aging conditions (Oliveira et al., 2011a). However, plants contain numerous antioxidant compounds, both enzymatic and non-enzymatic, which act to prevent oxidative damage by scavenging free radicals before they attack membranes or other seed components (Bhaskaran and Panneerselvam, 2013). Some protective mechanisms involving free radical and peroxide scavenging enzymes, such as (CAT), (POX), (APX) and (SOD), have been evaluated within the mechanism of seed aging (Espanany et al., 2016). Soil salinity may affect the germination of seeds and seedling establishment either by creating an osmotic potential external to the seed and roots, preventing water uptake, or through the toxic effects of sodium ion and Chlorine−ions on the germinating of the seed and plant growth (Iqbal and Ashraf, 2013). In addition to ionic and osmotic components, salt stress, e.g. accelerated aging of seeds, also leads to oxidative stress through an increase in reactive oxygen species (ROS), such as, hydrogen peroxide (H2O2) and hydroxyl radicals (OH) (Bhaskaran and Panneerselvam, 2013).

Priming Effect on the Physiological Potential of Maize Seeds under Abiotic Stress
Seed priming may be an alternative for improving seed vigor. Priming may be performed with the use of substances Journal of Biology, Agriculture and Healthcare www.iiste.org ISSN 2224-3208 (Paper) ISSN 2225-093X (Online) Vol.10, No.14, 2020 that contribute to the expression of the seed physiological potential (Batista, 2016). Seed priming may promote more balanced germination rates and higher germination speed, in addition to faster seedling growth under adverse conditions, for instance, under a biotic stress (Arif et al., 2014). However, few studies have been conducted on seed priming using the amino acid phenylalanine, which is a precursor of phenolic compounds that increase in response to different types of stress, e.g., related to the plant defense systems and adaptation to adverse situations (Stangarlin, 2011). According to Batista (2016), priming with chemical enhances physiological seed quality, producing seeds with high tolerance to stress under high temperature.
2.6. Effect of Seed Priming on Seed Vigor and Early Growth in Maize 2.6.1. Under suboptimal temperature condition Low temperature is one of the major environmental factor that has a significant influence on the growth and development of plants (Farooq et al., 2008a).The negative impact of low temperatures on plant metabolism can be detected from the cellular level to the level of the whole plant (Gay et al., 2008).The potential visual symptoms of chilling injuries in chilling-sensitive plants are leaf and hypocotyls wilting, the appearance of surface pits and large cavities, leaf necrosis, accelerated aging and the rupture of injured tissues, delayed, partial, or uneven ripening and growth decreasing, low temperature stress disturbs cells ultra-structure, enzyme activity, mitochondrial respiratory activity and electron transport (Gay et al., 2008).Accord mining to Saeidnejad et al., (2012) review that low temperature decreased maize seed germination parameters, seedling emergence and growth. Low temperature had deleterious effect on membrane stability, relative water content, starch metabolism and antioxidant activities (Farooq et al., 2008a). 2.6.2. Under optimum temperature conditions The optimum temperature for the germination of maize seed ranges from 25 to 28 °C. A stressful condition in germination lowers the plant population, which leads to reduction of grain yield (Radić et al., 2009).

Different Effects of Seed Priming Techniques can Improve Seed Vigor and Early Seedlings Growth.
There are several priming techniques, such as hydro priming (Kaya et al., 2006), osmo priming (Foti et al., 2008), halo priming , matrix priming (Zhang et al., 2007) and bio priming (Begum et al., 2010).The two most commonly used seed priming methods are hydro priming and osmo priming.
 Hydro priming Hydro priming is the simplest method of seed priming, which relies on seed soaking in pure water and re-drying to original moisture content prior to sowing. (Goswami et al., 2013).It is easily available and uncostly pre-sowing treatment, where seed hydration is achieved by soaking seeds in water (Casenave and Toselli, 2007). Kaya et al. (2006) According to this review hydro priming increased germination and seedling growth under salt and drought stress during germination in sunflower. Hydro-priming plays an important role in the seed germination, radical and plumule emergence in different crop species under saline and non-saline conditions and also have beneficial effect on enzyme activity required for rapid germination. (Rahman et al., 2011).
Beneficial effect of hydro priming on seed germination and seedling growth under both optimal and stress conditions, in various crop plants such as chickpea, maize, rice mung bean and capsicum has been observed (Posmyk andJanas, 2007 and. Harris (2006) has reported improvement in seed yield in various crops at farmer's field by seed priming with water. Caseiro et al., (2004) found that hydro-priming was the most effective method for improving seed germination of onion, especially when the seeds were hydrated for 96 hr compared to 48 hr. The main disadvantages of hydro priming is uncontrolled water uptake by seeds (Caseiro et al. ,2004).This is a consequence of free water availability to seeds during hydro priming, so that the rate of water uptake depends only on seed tissue affinity to water (Caseiro et al. ,2004).
 Bio priming Bio priming involves seed imbibition together with bacterial inoculation of seed (Gulick et al., 2012). As other priming method, this treatment increases rate and uniformity of germination, but additionally protects seeds against the soil and seed-borne pathogens. (Gulick et al., 2012). It was found that bio priming is a much more effective approach to disease management than other techniques such as pelleting and film coating (Muller and Berg, 2008). Nowadays, the use of bio priming with plant growth-promoting bacteria as an integral component of agricultural practice (Timmusk et al., 2014). In pearl millet, bio priming with Pseudomonas fluorescent isolates enhanced plant growth and resistance against downy mildew disease (Raj et al., 2004). Bio priming with rhizo bacteria improved germination parameters of radish seeds under saline conditions (Kaymak et al., 2009).
 Osmo priming It is standard priming method that involves the use of adverse osmotic solution like mannitol, polyethylene glycol or salts such as chlorides, sulphates, nitrates to control water potential (Chen et al., 2010;Papastylianou and Karamanos, 2012). The usefulness of osmo priming with Potassium Nitrite (KNO3) was shown in different plant species (Kaya et al., 2006;Eskandari and Kazemi, 2011).Osmo priming is the most widely used type of seed priming in which seeds are soaked in aerated low water potential solution. Priming of seeds in osmoticums has Journal of Biology, Agriculture and Healthcare www.iiste.org ISSN 2224-3208 (Paper) ISSN 2225-093X (Online) Vol.10, No.14, 2020 been reported to be an economical, simple and a safe technique for seedling establishment and crop production under stressed conditions (Guzman and Olave, 2006).  Solid matric priming Solid matrix priming (SMP), matric conditioning in which water uptake by seeds is controlled (McDonald, 2000). The use of solid medium allows seeds to hydrate slowly and simulates natural imbibition process occurring in the soil (McDonald, 2000).
 Halo priming Halo-priming refers to soaking of seeds in solution of inorganic salts i.e., sodium chloride (NaCl), Potassium Nitrite ( KNO3) and Calcium dichloride ( CaCl2) e.t.c. A number of studies have shown a significant improvement in seed germination, seedling emergence and establishment and final crop yield in salt affected soil in response to halo-priming 2006). Priming with sodium chloride (NaCl) and Potassium chloride (KCl) was helpful in removing the deleterious effects of salts (Iqbal et al., 2006). It is a pre-sowing soaking of seeds in salt solutions, which enhances germination and seedling emergence uniformly under adverse environmental conditions and normal condition. Inorganic salts are used. Review the effects of sodium chloride (NaCl) priming with potassium Nitrite ( KNO3) on the germination traits and seedling growth of four Helianthus annuus Cultivars under salinity conditions and review that germination percentage of primed seeds was greater than that of un-primed seeds ( Bajehbaj, 2010).
 Hormonal priming It is soaking of seed in hormone solution is referred as hormonal priming. GA3, Salicylic acid, Ascorbic acid, Cytokine's etc. can be used for this investigated the primed seeds of carrot, onion and tomato showing that priming these seeds with GA3 increased the germination percentage and rate (fzal et al., 2006).Review that the effect of hormonal priming with ABA, salicylic acid, or ascorbic acid on Wheat germination and seedling growth under normal and saline conditions (Bahrani and Pourreza, 2012).

Effect of Seed Priming on Maize Seedling Emergence
Different factors, such as soil moisture stress, temperature extremities, and soil salinity, poor seed bed preparation, weed competition, low seed quality, and extreme disease pressure adversely affect the emergence of maize seed. Seed priming could be used as a viable technology to improve seedling establishment. Rapid and uniform emergence has been achieved by seed priming in some field crops (Murungu et al., 2004).

Importance of Seed Priming in Plant G
 Germination Primed seeds enhanced uniform seedling emergence which may contribute to regular crop establishment, it often exhibit an increased germination rate and greater germination uniformity (Galhaut et al., 2014).Priming may also induce structural and ultra-structural modifications that could facilitate subsequent water uptake and attenuate initial differences between the seeds in terms of imbibition, thus resulting in a more uniform germination (Galhaut et al., 2014). In mung bean plants, faster seedling establishment resulting from priming may contribute to a total increase in yield up to 45% (Rashid et al., 2004). Priming-induced increase in germination may be associated to a change in plant hormone biosynthesis and signaling. Priming has been reported to increase gibberellins (GA)/abscisic acid (ABA) ratio (El-Arab et al., 2006) and this may be a direct consequence of a priming impact in gene expression pattern (Schwember et al., 2010). Ethylene also directly influences germination speed and percentage. Increase in ethylene production during priming may promote endo-β-mannase activity facilitating endosperm weakening and post-priming germination (Chen and Arora, 2013).
 Plant growth and development Plants produced from primed seeds often exhibit a faster growth than unprimed ones (Chen and Arora, 2013). The beneficial impact of priming on plant growth may be due to an improved nutrient use efficiency allowing a higher relative growth rate (Muhammad et al., 2015). A higher growth of seedlings issued from primed seeds may also be analyzed in relation to a direct impact of pretreatment on cell cycle regulation and cell elongation processes (Chen and Arora, 2013). The growth parameters of chickpea were significantly affected by seed priming (Guptaand Singh, 2012).
 Yield Yield increase may also result from a higher plant density observed as a -consequence of priming-induced increase in germination percentage (Murungu et al., 2004 andHarris et al., 2004). Seed priming treatment resulted in increased crop growth rate in treated sets which encouraged deposition of more photo assimilates in key plant parts, greatly affecting the final yield (Srivastava and Bose, 2012). Highest grain yield of Pusa Basmati 1121 was obtained with hydro-priming at 60 kg/ha of N application applied in 3 splits (Mahajan et al., 2011). Binang et al. (2012 also demonstrated that priming had a significant effect on the number of tillers number of fertile panicles, and consequently grain yield of new rice varieties.