Effect of Various Seed Priming Methods on Germination Characteristics of Black Gram

Black gram (Vigna mungo L. Hepper) is a leguminous crop belonging to the family Leguminoseae and subfamily Papilionaceae. It is popular among the countries around Indian sub-continent and is one of the most consumed legumes in Nepal. It is grown in rainy season mainly in a cereal-pulse cropping system primarily to conserve soil nutrients, soil moisture and soil itself. It not only helps in enhancing soil fertility through biological nitrogen fixation but also increases the yield of the following crop [1]. It is normally grown in areas with an average temperature of 27-30ºC and an annual rainfall of 600-1000mm. In higher rainfall areas it may be grown in the dry season on residual moisture. A dry harvest period is preferable as this forces the crop to mature and reduce the risk of weather damage. It prefers to grow on heavier, well-drained; cotton-black soil with pH 6-7 but it is also grown on lighter soils. Black gram has good tendency to resist drought but frost and prolonged cloudiness can create serious problems in its cultivation. Since it is cultivated on marginal lands under rainfed conditions, lack of nutrients and moisture has resulted in poor germination and establishment. Germination is one of the yields determining factors but it is a challenge to facilitate good germination in soil with poor fertility. Seed priming is accepted technique to improve seed germination. 

Priming is a pre-sowing treatment in which seeds are partly hydrated such that there is initiation of germination process with no observable radicle emergence [2]. Increase in germination rate, greater germination uniformity, vigorous growth, early flowering and higher yield can be observed with the use of primed seeds [3,4]. Various priming methods are available to enhance seed germination. Hydro-priming is achieved by submerging seeds in water whereas in osmo-priming, osmotic solutions having low water potential are used to control water uptake. In halopriming seeds are soaked in solutions of inorganic salts [5]. There are many studies reporting the effects of priming on seeds. According to [6] priming improves the performance of seeds by coordinated germination. In a study conducted by [7] in Black gram, the improvement of primed seeds to germinate in field conditions could be credited to activation of cells which resulted in enhancement of mitochondrial activity leading to the formation of more high energy compounds and vital biomolecules which were made available in early germination stage [8] concluded that seed priming is a suitable method to improve germination, reduce seedling emergence time and improve stand establishment and yield [9] conducted an experiment to evaluate effect of seed priming on seed germination and yield of corn and found that priming methods and duration increased germination percentage and germination rate [10] conducted an experiment to study the influence of halopriming and organic priming on germination and seed vigour in Black gram and concluded halopriming showed better result in comparison to organic priming. Similar conclusion was obtained from [11] in his experiment to observe the suitable method of priming for wheat seeds [12] concluded that priming with NaCl can prepare a suitable metabolic reaction and can improve seed germination under undesirable condition such as salinity stress [13] reported that maximum radicle length of cultivar Sardari (bread wheat) was obtained at 20% PEG6000 solution primed for 24h where germination rate and radicle length decreased with increasing concentrations.

The experiment was conducted in the Agronomy Lab of Institute of Agriculture and Animal Science, Sundarbazar, Lamjung. Locally available Black gram seeds were used in the experiment. The experiment was laid out in Completely Randomized Design (CRD) replicated thrice using Hydropriming, Osmo-priming (PEG-600@1%, 2%, 5% and 10%), Halo-priming (NaCl@ 1% and 2%) and Hormonal priming (GA3 @5 and 10ppm) as treatments and compared with unprimed seeds as control treatment. Presoaking was carried out for 24 hours at 25ºC followed by shade drying for 48 hours except in case of hormonal priming in which presoaking was carried out for 2 hours at room temperature. Before the commencement of experiment, petri and solution dishes were thoroughly cleaned and seeds were rinsed with distilled water. Priming solutions were made with related concentrations using distilled water based on the formula: 

• X% solution = x gm solute + (100-x) ml of solvent (for PEG 600 and NaCl)
• X ppm = x mg of solute + (1000-x) ml of solvent (for GA3) 

Petri dishes each having two layers of germination paper and 25 seeds were provided with control medium which were placed in a germinator at 25ºC for 8 days and data were collected at every 24 hours Seeds with ruptured seed coat and radical length of more than 2mm were considered to be germinated [14,15]. In table 1 each Petri dish ten seedlings were randomly selected for measurement of root length and shoot length. Seedlings were put in different envelopes and oven dried at 72ºC for 48 hrs to measure the dry weight. Germination parameters like germination percentage, germination index, mean germination time and coefficient of velocity of germination along with seedling parameters like vigor index 1&2 were calculated. 

Table 1: Parameters calculated with details

Seed germination: 

Seed priming had significant effect on germination percentage over unprimed one as shown in Table 2. Hydropriming and hormonal priming with GA3 couldn’t improve germination percentage compared to control. As the concentration of PEG600 was increased above 1%, germination percentage also increased up to 5% and then it decreased with higher concentration. There was increase in germination percentage with increase in NaCl level.

Table 2: Effect of different priming methods on germination percentage, root length, seedling length, dry weight, seedling vigor index-1 and seedling vigor index-2. 

Seedling length, dry weight and vigor: 

Table 2 revealed that Hydoprimed seeds induced longest root length while seeds primed with lower concentration of PEG600 and NaCl induced longer roots as compared to control. Priming with PEG 2% resulted in better shoot length. Better dry weight accumulation was seen with hydroprimed seeds. Osmopriming only improved dry weight accumulation at 2% concentration. Although halopriming induced better root length at lower concentration.

it failed to improve dry weight. Hormonal priming wasn’t able to induce better seedling length, dry weight accumulation and vigor. Overall priming with PEG 5% gave best results in germination and seedling characteristics. Hydropriming of seeds didn’t improve SVI-1 but improved SVI-2. Seedling vigor increased above 1% up to 2% and decreased with increasing concentration. Halopriming and hormonal priming couldn’t significantly influence seedling vigor. 

Speed of germination: 

Speed of germination was analyzed with the help of germination index, coefficient of velocity of germination and mean germination time as shown in table 3. Though effect of priming on germination index and coefficient of velocity of germination was inconclusive, overall germination has been improved. Analysis of mean germination time gave satisfactory results to observe effect of seed priming. Unprimed seeds took maximum time to germinate. Hydropriming also reduced the germinating time. As the concentration of PEG increases above 1% MGT decreases up to 5% then MGT increases. Halopriming and hormonal priming gave better speed of germination at lower concentration and with increasing concentration germination slowed down. 

Table 3: Effect of different priming methods on speed of germination

Seed priming seems to influence the germination characteristics and initial seedling growth of Black gram. Hydropriming had an adverse effect on germination percentage but a positive role towards speed of germination also found similar results. Earlier and synchronized germination in hydroprimed seeds is may be due to increased metabolic activities [21]. This can be associated with longer root length resulting in greater dry matter accumulation and seedling vigor [22] found that high seedling dry weight was seen with hydroprimed seeds. 

Osmopriming with PEG gave the best results in germination and its speed which is due to reactive oxygen species which hastened amylase activities and starch breakdown [23,24] found that osmopriming can enhance DNA replication and DNA repair and promote mobilization of reserved materials which contribute to initiate seed germination. Overall parameters are positively affected by increasing concentrations of PEG but further increase can reduce the seedling parameters such as germination percentage and seedling length. This reduction in germination and length is due to increase in osmotic potential in primed seeds which can alter rate of water uptake. 

Although haloprimed seeds performed better than seeds treated with GA3, its performance is inferior to osmopriming. Halopriming accelerated seed germination at lower concentration due to anti-oxidant increment as glutathione and ascorbate in seed which led to higher germination speed via reduction of lipid proxidation activity [25]. Halopriming slowed down germination at higher concentration which may be due to toxic effect of sodium and chloride ions or by creating osmotic pressure [26]. According to [27], there is increase in germination time and decrease in water uptake with increasing osmotic potential. This has led to poor root and seedling length resulting in fewer dry weight accumulation and poor vigor.

Hydropriming of seeds is a cheap and convenient way to improve crop establishment. Halopriming of seeds with low osmotic potential of NaCl of 1% gives better crop establishment than unprimed one. Hormonal priming with GA3 didn’t improve germination and seedling characteristics but slightly reduced germination time at lower concentration. Maybe the effect of hormonal priming will be more significant if grown in different medium. Osmopriming with PEG600 up to 5% concentration was found beneficial for better germination and crop establishment.