Effect of hydropriming on seedling growth of basil (Ocimum basilicum L.).
Basil (Ocimum basilicum L.) belonging to the plant family Lamiaceae, subfamily Nepetoideae, and the genus sensu lato, comprises 65 species. Basil is an annual, 20-60 cm long, white-purple flowering plant, which is originally native to India and other regions of Asia. . Basil is cultivated in agroclimes between 7 to 27 C, with 0.6 to 4.2 m annual precipitation and soil pH 4.3 to 8.2. Rapid and uniform field emergences of seedlings are two essential pre-requisites to increase yield and quality in annual crops . Uniform performance of seeds of cultivated plants is seldom achieved, where a seed lot represents an amalgam of individuals, each with different germination vigor . Various prehydration or priming treatments have been employed to increase the speed and synchrony of seed germination . Hydrating seeds with water and re-drying them before they complete germination is a technique which minimizes the use of chemicals and avoids discarding materials that may be undesirable to the environment . This simple, low cost and low risk intervention also had positive impacts on the wider farming system and livelihoods and the technology has proved highly popular with farmers [17,18,14]. Improved seed invigoration techniques are known to reduce emergence time, accomplish uniform emergence, and give better crop stand in many horticultural and field crops. These include hydropriming, osmoconditioning, osmohardening, hardening, hormonal priming, and soaking before sowing . Seed priming techniques such as hydropriming, hardening, osmoconditioning, osmohardening, and hormonal priming have been used to accelerate emergence of roots and shoots, more vigorous plants, and better drought tolerance in many field crops like wheat , chickpea , sunflower  and cotton . But in production of medicinal plants, seed germination is very important problem. The seeds are occasionally sown in seedbeds having unfavorable moisture because of the lack of rainfall at sowing time , which results in poor and unsynchronized seedling emergence . Seed priming is a treatment that partially hydrates seeds so that germination process begins, but radical emergence does not occur. Priming has been widely reported to enhance seed germination performance of various species of field crops, vegetables, and other plants . Short time hydration treatments, e.g. hydropriming, humidification (incubating seed at high relative humidity) have been widely used to increase seed vigour and extend seed longevity in many plant species . Re-drying after priming is a critical step for maintaining seed quality. Rapid drying following priming can damage seeds resulting in the loss of advancement obtained during priming . Good seedling establishment is an important constraint to such crop production . Poor seedbed, low quality seed, environmental stresses such as high and low temperature and salinity constrains to good establishment include [42,40]. A robust seedling establishment enhances competitiveness against weeds, improves tolerance to environmental stresses and maximizes biological and grain yields . Several approaches including, hardening, seed priming, seed soaking and seed coating have been employed to precondition seeds to improve germination and seedling growth of various crops . Seed priming treatments such as osmopriming, hydropriming, matricopriming, hormonalpriming have been employed to accelerate the germination, seedling growth and yield in most of the crops under normal and stress conditions . Although, the mechanism of seed priming treatments is not fully understood, it has been observed that physiological and biochemical changes take place during the seed treatments . Seed priming accelerates seed germination and seedling establishment under both normal and stressful environments . Priming is one of the physiological methods, which improves seed performance and provides faster and synchronised germination . Hydropriming is the simplest approach to hydrate seeds and minimize the use of chemicals. However, if the seeds are not accurately hydrated, hydration rate cannot be exactly controlled. It was observed that hydropriming practically ensured rapid and uniform germination accompanied with low abnormal seedling percentage [33,36]. Seed quality (viability and vigor) can have a profound influence on the establishment and the yield of a crop. Healthy plants with well developed root systems can better withstand adverse conditions and a vigorous early seedling growth has bean shown to be associated with higher yields . The vigor of seeds can be improved by techniques generally known as seed priming, which enhance the speed and uniformity of germination . The principle of priming is based on the fact that it is possible to hydrate seed in some ways at a moisture level sufficient to initiate the early events of germination but not sufficient to permit radical protrusion. Methods of seed priming can be divided into two groups depending on whether water uptake is uncontrolled (hydropriming) or controlled (osmotic - priming and solid matrix priming) . Water uptake during hydropriming is governed only by the affinity of the seed tissue for water. Seeds are imbibed on moistened blotters or soaked in water. Because water is not limited, seeds can eventually germinate assuming that they are viable, not dormant, and optimal conditions are provided. Therefore, in uncontrolled systems the process must be arrested at a specific time to prevent radical protrusion. In controlled priming the amount of water available for seeds is restricted or the water potential of priming medium can be regulated. Although priming is one of the physiological methods, which improves seed performance and seed faster and synchronized germination , it has been shown that the longevity of primed seeds in storage is often reduced [41,9,38]. Whether the benefits of priming on seed performance could be maintained during dry storage still remains unknown. Seed priming started with Greek farmers who soaked cucumber seeds in milk or honey before sowing to increase germination and emergence .
Materials and methods
In order to determine the impact of hydropriming on germination of basil seeds, an experiment was conducted in 2010 at Laboratory Sciences, Islamic Azad University Shahr-e-Qods Branch by a completely randomized design with three replications and the first, seed viability was determined by Tetrazolium test method. After disinfecting, seeds were put in disinfected Petri dish. Each Petri dish contained 100 seeds. Afterwards dried seeds were located in Petri dishes and treated with distilled water at temperature of 25[degrees]C for seven days. Statistical experimental design was randomized completely block, with three replications. The differences between the means were compared using Duncan's test (P < 0.05).
Three replicates of 100 seeds were put between double layered rolled. The rolled paper with seeds was put into sealed plastic bags to avoid moisture loss. Seeds were allowed to germinate at 25 [+ or -] 1[degrees]C for 8 days. Germination was considered when the radicles were 2 mm long. Germination percentage was recorded every 24 h for 8 days. Root length and shoot length were measured after the 8th day. Seedling vigour index was calculated by the following formula:
Germination percentage x Seedling dry weight = Seedling vigour index
Data analyses were performed using the Spss statistical software (Version 15). Mean separations were performed by Duncan's multiple range test (DMRT) at 5% level.
Results and discussion
The results showed that the effect of hydropriming was significant on germination in P [less than or equal to] 0.05. Germination percentage, mean germination time and seedling dry weights of basil were significantly affected hydropriming (P [less than or equal to] 0.05). Germination Percentage for P2 (hydropriming for 8 h) and P3 (hydropriming for 12h) was significantly higher than that for P1 (for 4 h) (Table 1). Hydropriming of seeds in water for 8 and 12 h before sowing improved field performance of basil. The efficiency of seed hydropriming for better seedling establishment is also reported in barley , lentil  and chickpea . However, the resultant effect of priming depends on duration of seed soaking [3,15]. Kumar et al.  found safe maximum lengths of time for which seed should be primed, beyond which it could be damaging to the seed or seedling. Recommended safe limits were 24 h for maize and rice, 10 h for chickpeas and 8 h for pearl millet. In our research, optimal time of hydropriming for pinto bean seeds was 7 h, statistically similar with 14 h. A longer time of hydro-priming seems to have a negative effect on seed quality of pinto bean. Optimum stand establishment and early achievement of maximum ground cover are essential for the efficient use of resources like water and light [27,14]. There is a linear relationship between ground cover and light interception . Consequently, ground cover is strongly related with plant biomass, pods per plant, grains per pod, grains per plant, harvest index and grain yield per unit area. Ground cover also has the practical advantage as a simple, quick and nondestructive measurement, allowing frequent sampling . Therefore, it can be used as a reliable index to predict the yield potential of pinto bean cultivars. The superiority of Talash and COS16 in ground cover led to the production of comparatively more plant biomass, pods and grains per plant and grain yield per unit area. Although mean grain weight of Khomain was higher than that of other cultivars, but it produced the lowest number of pods and grains per plant, leading to lower grain yield per unit area. This is also reflected in significantly positive correlation of grains per plant and negative correlation of 1000 grain weight with grain yield per unit area. Therefore, photo-assimilates directed to less number of grains in khomain and resulted in production of comparatively larger grains. However, this superiority was not sufficient to compensate the reduction in number of grains per plant, compared with other cultivars. Similar results were reported for black bean  and common bean . No significant interaction of seed priming x cultivar on measured traits suggest that hydropriming for 7 h is the best pretreatment to improve field performance of all pinto bean cultivars. However, hydropriming duration may differ by plant species [5,39,17,14]. Like germination percentage, prime seeds had lower MET compared with un-primed seeds. These positive effects are probably due to the stimulatory effects of priming on the early stages of germination process by mediation of cell division in germinating seeds [37,36]. There are several reports that seed priming can homogenize seed germination in a short period of time [23,29,44].
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Kasra Maroufi, Young Researchers Club, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran.
(1) Hossein Aliabadi Farahani, (2) Payam Moaveni and (1) Kasra Maroufi
(1) Young Researchers Club, Shahr-e-Qods Branch, Islamic Azad University, Tehran, Iran.
(2) Islamic Azad University, Shahr-e-Qods Branch, Tehran, Iran.
Table 1: Means Comparison Hydropriming Gremination Seedling dry Seedling (Hourse) percentage wegheit vigour 4 82 c 0.060 b 4.92 c 8 85 b 0.061 b 5.18 b 12 91 a 0.079 a 7.18 a Means within the same column and factors, followed by the same letter aren't significantly difference.
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|Title Annotation:||Original Article|
|Author:||Farahani, Hossein Aliabadi; Moaveni, Payam; Maroufi, Kasra|
|Publication:||Advances in Environmental Biology|
|Date:||Jul 1, 2011|
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