dormancy and seed germination of plant

Dormancy and Seed Germination of Four Different Plant Species of the Family Leguminosae

Studies on dormancy and seed germination of four different plant species of the family leguminosae which includes, Centrosama pubescens, Sesbania sesban. Sesbania rostrata and Clitoria ternatea were carried out. This involves the use of dormancy-releasing methods like the use of the chemicals; Sulphuric Acid (H2 SO4 ), Hydrogen Peroxide (H2 O2), Ethanol (C2 H5 OH), Methanol (CH3 OH), and Potassium nitrate (KNO3), Hot water treatment, and hormones like Gibberellins and Kinetin.
M.Sc Thesis by Uchenna Charles Njimogu.

ABSTRACT

Studies on dormancy and seed germination of four different plant species of the family leguminosae which includes, Centrosama pubescens, Sesbania sesban. Sesbania rostrata and Clitoria ternatea were carried out. This involves the use of dormancy-releasing methods like the use of the chemicals; Sulphuric Acid (H2 SO4 ), Hydrogen Peroxide (H2 O2), Ethanol (C2 H5 OH), Methanol (CH3 OH), and Potassium nitrate (KNO3), Hot water treatment, and hormones like Gibberellins and Kinetin. The preliminary germination test on intact seeds in hot water for two minutes before germination for Centrosena pubescens and Sesbania sesban and fifteen minutes for Clitoria ternatea and Sesbania rostrata recorded the highest percentage of germination when compared to the control. Treatment of intact seeds with chemicals especially sulphuric acid and hydrogen peroxide were more efficient in breaking seed dormancy while the use of kinetin as a hormone has an edge over gibberellins in the breaking of seed dormancy. The presence of cuticle, macrosclereids, and osteosclereids which are impermeable to water and gas immensely contributed to the high level of dormancy in the seeds as seen in the research. The information gathered in this research will go a long way in eradicating or tackling the problems of dormancy or improving the propagative methods of most forest plants. All these will help the foresters to have access to producing the seedlings to meet the population demands.



CHAPTER ONE

Introduction

In plants, seed germination must occur in the right place and at the right time, for this reason, most species have mechanisms that delay germination, such as seed dormancy (Fenner and Thompson, 2005). The definitions of dormancy in seeds have been a source of controversy (Fenner and Thompson, 2005; Finch-Savage and Leubner-Metzger, 2006). The definition of dormancy that has been proposed recently is that dormancy is an innate seed property determined by genetics that defines the environmental conditions in which the seed can germinate (Finch-Savage and Leubner-Metzger, 2006). Five classes of seed dormancy are recognized, and one of them is physical dormancy (Baskin and Baskin, 2004), which is caused by the seed coat that prevents imbibition of water (Morrison et al., 1998;  Smith et al., 2002).

Physical dormancy refers to seeds that are water-impermeable and is known to occur in 17 families of angiosperms, including the Fabaceae (Baskin and Baskin, 2000; Funes and Venier, 2006).

1.1.0              Sesbania sesban

1.1              Botany

The species, S. sesban (L.) Merrill belongs to the Sub-family: Papilionoideae, Family: Leguminosae or Fabaceae (Dinendra and Azad-ud-doula, 2001; Pandhare et al., 2011; Gupta et al., 2011). The exact origin of S. sesban is unclear, but it is widely distributed and cultivated throughout tropical Africa and Asia. It has also been introduced in tropical America (Mani et al., 2011; Heering et al., 1996; Wiegand et al., 1995). It is an exotic plant to Ethiopia (Mekoya et al., 2009a; Orwa et al., 2009) and is originally from East Africa.

The greatest species diversity occurs in Africa (distributed widely in northern, eastern, southern, and central Africa) with 33 species described (Gillett, 1963; Degefu et al., 2011; Yang et al., 2003; Vadivel et al., 2012; Gupta et al., 2011). Five varieties of S. sesban are recognized botanically (Mani et al., 2011; Gutteridge, 1993) viz., S. sesban var. sesban, S. sesban var. bicolor, S. sesban var. nubica, S. sesban var. zambesiaca, and S. sesban subsp. punctata. The first three varieties are all similar and have been noted for their vigorous growth and high yields, while the rest are less known varieties (Gutteridge, 1993). If the trees planted are widely spaced they usually develop many side branches. The many branches give the tree a shrubby appearance (Orwa et al., 2009).  The scientific classification of Sesbania sesban is given below.

Taxonomical Classification

Kingdom:       Plantae

Unranked:      Angiosperms

Unranked:      Eudicots

Unranked:      Rosids

Order:             Fabales

Family:           Fabaceae

Genus:            Sesbania

Species:           S. seban

Binomial name

Sesbania sesban L.

1.1.2 Habit

S. sesban is a multipurpose tree with different parts of the plant (bark, root, seed, leaf, and stem).  It is a short-lived shrub or small tree up to 8 m tall. Its leaves are pinnately compound, 2-18 cm long with 6-27 pairs of linear-oblong leaflets (26 x 5 mm). The raceme has 2-20 flowers which are yellow with purple or brown streaks on the corolla. Pods are subcylindrical, straight or slightly curved up to 30 cm long and 5 mm wide containing 10-50 seeds.               

Sesbania sesban is a narrow-crowned, deep-rooting single or multi-stemmed shrub or small tree,   1-7 m tall. The trees usually have the main stem but may develop many side branches if widely spaced. The many branches give the tree a shrubby appearance, often tending towards a spreading habit due to its wide branching angle (45-60 deg. mostly).

  • Leaves are paripinnate, long (compound 12 to 18 cm long) and narrow; leaflets in many pairs (made up of 6 to 27 pairs of leaflets) (Mani et al., 2011), rounded or oblong, usually asymmetric at the base, often glaucous and stipules are minute or absent.  
  • Flowers attractive, yellow
  • Variegated or streaked, seldom white, large or small on slender pedicels, solitary or paired in short axillary racemes, usually unpleasantly scented; all petals long-clawed, standard orbicular or obovate.
  • Pods pale yellow, linear, usually 10-20 cm long, cylindrical or compressed, rarely oblong; up to 40 seeds are found in a pod; seeds oblong or subquadrate, brown or dark green mottled with black. Sesbania sesban is propagated through seeds.

1.1.3  Habitats / Environmental Adaptation

It grows well in the subtropics and is significant in extending the nitrogen-fixing forage trees into cooler, higher-elevation regions of the tropics up to 2,000 m. It is outstanding in its ability to tolerate waterlogging and is ideally suited to seasonally waterlogged environments. When flooded, it initiates floating adventitious roots and protects its stems, roots, and nodules with spongy, aerenchyma tissue.  However, its tolerance of highly acid, aluminum saturated soils is not known (Gutteridge,1993).

1.1.4        Distribution

Sesbania sesban is mainly distributed by man, itcan be found in Africa countries such as Nigeria, Egypt, Ghana, Sudan, Uganda, Senegal, Gambia, Guinea, Mali, Niger, South Africa Etc.

In Asia countries it can be found in these countries: Oman, Saudi, Arabia, Yemen, Afghanistan, Iran, Iraq, China, India, Laos, Thailand, Vietnam, Etc. And Also in the Northern Territory of Australia, Etc.

1.1.5  Economic Importance/ Uses

S. sesban got promoted by different organizations in Ethiopia in the 1970s, that different exotic multipurpose fodder trees and alleviate feed shortages, maintain soil fertility, and prevent land degradation (Mekoya et al., 2009b).  In some part of Ethiopia, S. sesban is a Nitrogen-fixing and deep rooting shrub with good-quality foliage, (Desaeger and Rao, 2001) and serve as a protein supplement to poor-quality roughages or as a substitute for commercial protein supplements (Mekoya et al., 2009). Apart from this, its capacity to control soil erosion and hence restore and maintain soil fertility makes it a useful component of traditional agroforestry. Therefore, promoting S. sesban in Ethiopia, where more than 80% of the people are dependent on plants for their health service, (Wondimu et al., 2007). S. sesban tree has a high level of foliage nitrogen and is an excellent supplement to protein-poor roughage (Sabra et al., 2010; Manaye et al., 2009; Orwa et al., 2009). The leaves and tender branches of this tree have high levels of protein (with 20 to 25% crude protein) and are easily digestible when consumed by ruminants. It has a long history of use as a source of cut-and-carry forage (Naik et al., 2011).

  • ANTI-INFLAMMATORY

Effect S. sesban leaf is reported to be used in the treatment of inflammatory rheumatic conditions (Nirmal et al., 2012; Shaikh et al., 2012). Reproductive and milk production enhancement Supplementation of ration with S. sesban is reported to improve the reproductive performance of sheep; and its inclusion up to 30% of the ration improved feed intake, growth rate, the onset of puberty, and sexual development (Sabra et al., 2010; Mekoya et al., 2009a). Moreover, ewes supplemented with S. sesban at 30% of the ration showed a 13% increase in milk production over ewes supplemented with concentrates (Mekoya et al., 2009b).

  • ANTI-DIABETIC ROLE

Different research works (Boddupalli et al., 2012; Pandhare et al., 2011; Ramdas et al., 2010,2012) reported that the aqueous leave extract of S.sesban has an anti-diabetic effect which could be associated with the presence of flavonoids. More specifically, to manage type II diabetes (Vadivel et al., 2012) recommend the use of S. sesban seeds as a natural source of dietary antioxidants.

  • BIOENERGY SOURCE

The stem and thick branches of S. sesban are popular for firewood and charcoal production because it produces a relatively smokeless, quick kindling, and hot burning woody biomass in a short time (Heering, 1995; Orwa et al., 2009; Naik et al.,2011; ).

  • STIMULANT EFFECT

The crude drug extract obtained from the bark of S. sesban has been examined and found to have a potential central nervous system stimulant effect that can be explored for therapeutic advantage as an alternative treatment in medical conditions associated with dizziness and sedative (Naik et al., 2011; Pravin et al., 2012).

  • FIBER SOURCE

The bark of S. sesban can be used for making ropes and fishnet (Orwa et al., 2009).

  • ANTIOXIDANT EFFECT

The flower petals of S. sesban may be valuable natural antioxidant sources that protect the cells against the effect of free radicals by scavenging them and retard the progress of many chronic and degenerative diseases such as cardiovascular diseases and cancer (Kathiresh et al., 2011).

This activity is attributed to the presence of saponins and flavonoids (Mani et al., 2011) which make the plant potentially applicable in both the pharmaceutical and food industries (Kathiresh et al., 2011).

  • DECORATIVE FOOD INGREDIENT

Flowers of S. sesban are known to be added to stews and omelets in some areas, perhaps mainly as a decorative or festive ingredient in foods (Kathiresh et al., 2011; Orwa et al., 2009; Pravin et al., 2012).

  • ANTIMICROBIAL ACTIVITY

Studies also witnessed that extracts from S. sesban flower petals serve as antimicrobial activity (Kathiresh et al., 2012; Mythili and Ravindhran, 2012).In the traditional medicine system of Nigeria, the plant is pounded and mixed with milk and taken as an internal remedy for Guinea worm (Vadivel et al., 2012). Furthermore, Alagesa boopathi (2012) reported that decoction of the leaf is mixed with hot milk and given once a day for seven days for treatment of diarrhea, itches, and skin diseases.

  • LIVE SUPPORT

S. sesban can be used as live support for black pepper, grapes, cucurbits, and betel vine. In addition, its spreading canopies can serve as a shade tree for coffee, tea, cocoa, and turmeric (Kathiresh,2011; Orwa et al., 2009; Naik et al., 2011). It has also been used as a windbreak for bananas, citrus, and coffee (Orwa et al., 2009) and as fencing materials (Sarkar and Prodhan, 2001).

  • POLLUTED WATER AND SOIL TREATMENT

The ability of S. sesban to grow at different ammonium concentrations soil culture has been studied by different workers (Indieka and Odee, 2005; Dan et al., 2011; Dan and Brix, 2009), and it was shown that its seedlings can tolerate ammonium concentrations up to 800mg/L. This high tolerance suggests that this plant has potential for use in treatment systems of waste or polluted water (Indieka and Odee, 2005; Dan et al., 2011; Dan and Brix, 2009) And removal of heavy metals from the soil, that is, phytoremediation of sites contaminated with heavy metals (Yang et al., 2003; Gupta et al., 2011).

  • WEED CONTROL

leaf aqueous extract and dry residue of S. sesban could serve in the inhibition of germination and seedling growth of parthenium, which is currently considered as the most serious weed in Ethiopia in both arable and grazing lands as it caused severe crop losses (Tamado and Milberg, 2000).

dormancy and seed germination of plant

1.2      Sesbania Rostrata

1.2.1 Botany

Sesbania rostrata is a small semi-aquatic leguminous tree, in the genus Sesbania (Capoen, et al 2010). ‘The genus Sesbania belongs to the family Leguminosae and its subfamily is Papilionoideae. There are four subgenera of which Sesbania and Agati are of agricultural value. The genus Sesbania is much more important in Africa, and it has a large number of species. S. rostrata has seeds with a hard seed coat which prevents or delays germination. Taylor, G. B. (2005) to break this dormancy requires scarification, which can be done by different methods: physical abrasion of the seed coat, soaking the seeds in hot water, or concentrated sulphuric acid. The scientific classification of Sesbania rostrata is given below.

Taxonomical Classification

Kingdom:        Plantae

Unranked:       Angiosperms

Unranked:       Eudicots

Unranked:       Rosids

Order:              Fabales

Family:            Fabaceae

Subfamily:       Faboideae

Genus:             Sesbania

Species:           S. rostrata

Binomial name: Sesbania rostrata

                                Source: Bremek and Oberm

1.2.2           Habits

S. rostrata can be propagated from stem cutting or seed, growing slowly in the first 30 days, but growing sufficiently by 50-60 days to be incorporated.  Plants established from cutting grow 2 to 2.5 times faster in the first 42 days than seeded plants. Sesbania rostrata is a woody, erect, robust, annual, or short-lived perennial of about 1 to 3 m tall. 

The stem is covered with soft hairs and is 15 mm thick. Leaves are 7 to 25 cm long and paripinnate with 12 to 22 pairs of leaflets. Racemes contain 3 to 15 flowers on a rachis, and flowers are yellow. Pods are curved 15 to 22 cm long, and seeds are small, sub-cylindrical, and light to dark brown.

1.2.3           Habitats

S. rostrata grows naturally in waterlogged and fine-grained fertile soil deposited by water flowing over flood plains (alluvial soils. It tolerates freely drained, poorly drained, and flooded soils with moderate fertility, though it does not grow well in heavy clay soils. It occurs naturally in marshes, floodplains, on muddy river banks, and the edges of pools, but has also been recorded in open savanna.  It tolerates waterlogged soils and flooding to over 1 m deep.

S. rostrata tolerates a pH down to 4.3 to slightly alkaline, but nitrogen-fixation is reduced in acidic conditions. It grows in altitudes up to 1500-1600 m and can endure waterlogged soils and flooding over 1 m deep. It tolerates bimodal and summer rainfall patterns, heavy to medium clay soils, neutral pH, free and impeded soil drainage. It is adapted to low and moderate salinity but seed germination and growth decrease as salinity concentration increases. The ideal water requirement is 600-1000 mm rainfall. It is a tropical plant with an optimal temperature of 25º C. The addition of lime is highly acidic soils and phosphorus in soils with low fertility improves growth and nitrogen fixation of S. rostrata. S. rostrata is a short-day plant with a day length of 12-12.5 hrs. During shorter day lengths it flowers earlier, however, when day lengths are longer than 12 hrs, then it flowers later. Its use as green manure is limited to that part of the year with longer day lengths because during this period vegetative growth is extended and more biomass is produced.

1.2.4           Distribution

Sesbania has been reported in virtually all African countries from the tropical rainfall forests in Zaire to the Nile valley in the Egyptian desert. Sesbania rostrata can also be found in: Nigeria, Botswana, Cameroon, Central African Republic, Chad, Democratic Republic of Congo, Ethiopia, Madagascar, Malawi, Mali, Mauritania, Mozambique, Namibia, Niger, Senegal, Tanzania, Zambia, Zimbabwe, and It is mainly distributed by man.               

1.2.5  Economic Importance/ Uses

Ethnobotanical investigations in the central region of Burkina Faso have shown that Sesbania rostrata is used frequently and widely in traditional medicine to treat gastrointestinal infections, cardiovascular diseases and have antibacterial and antiviral activities (Nacoulma, 1996).

It forms a symbiotic relationship with Gram-negative rhizobia which leads to the formation of nitrogen-fixing nodules on both stem and roots. Capoen, et al (2010). It is mainly used as green manure to improve soil fertility due to its fast growth, high biomass production, and ability to convert large amounts of atmospheric nitrogen into a usable form for plants. Other applications include the production of high-quality forage for livestock and it is a source of fuel-wood. 

Many studies showed that natural antioxidants are more and more the subject of scientific research because of the therapeutic properties related to their structure. Recently, the role of natural antioxidants compounds for their ability to reduce the oxidative damage associated with many diseases such as aging, cardiovascular disease, cancer, inflammatory disease, skin disease, malaria, immune deficiency disease encourage some search for medicinal plants compounds (Fraga et al., 2010). Sesbania rostrata is primarily used as green manure to improve soil fertility. It can accumulate 100 kg/ha of nitrogen in 50 days. It can be used in alley-cropping systems and as a trap crop for insect pests in soybean and for nematodes such as Hirschmanniella oryzae and H. spinicaudata, which affect rice crops. It is used for livestock feed, it is eaten by sheep, goats, and sometimes camels, but unpalatable to cattle. In some countries, leaves are eaten by people, and it is also a source of fuelwood, dry stems serve as a fuel in Madagascar. Sesbania rostrata provides a readily available source of crude protein (CP) content for livestock which can be especially beneficial for small-scale farming. Sesbania is known for exceptionally fast growth rates as well as a very high affinity for association with several nitrogen-fixing rhizobia in the soil that cause the formation of numerous and large nodules in the plant roots. Members of this genus also have several potential uses including forage, poles for light construction, fuelwood, pulpwood, live fences, medicines, shade trees for other crops and gums. Fifty species of Sesbania have been described in tropical and subtropical regions of the world (Gillet, 1963; Burbidge, 1965). In Africa, the most dominant species is S. sesban (S. egyptica). However, there are several species of Sesbania in Africa with unknown agricultural value and these have not been evaluated in agronomic trials.

dormancy and seed germination of plant

Table 2.0        Species distribution of Sesbania in various regions of the world.

RegionNo. of speciesSource
Africa33Gillet, 1963
Australia10Burbidge, 1965
Hawaii7Char, 1983
AsiaUnknownChar, 1983

1.3      Centrosema Pubescens

1.3.1  Botany

Centrosema pubescens, common name centro or butterfly pea, is a legume in the family Fabaceae, subfamily Faboideae, and tribe Phaseolae. It is native to Central and South America and cultivated in other tropical areas as forage for livestock. Seeds of Centrosema pubescens have a mechanical dormancy that has to be broken by soaking the seeds for 3–5 minutes in water at 85 °C (Costa, et al 2009). The scientific classification of Centrosema pubescens is given below.

Taxonomical Classification

Kingdom:        Plantae

Unranked:       Angiosperms

Unranked:       Eudicots

Unranked:       Rosids

Order:              Fabales

Family:            Fabaceae

Tribe:               Phaseoleae

Sub tribe:         Clitoriinae

Genus:             Centrosema

Species:           C. pubescens  

Binomial name: Centrosema pubescens

            Source:            Benth

1. 3.2          Habit

C. pubescens is propagated by seed, planted directly into the ground, or spread over a field typically before the rainy season. It is a perennial trailing-climbing herb with a strong tendency to root at nodes of trailing stems,  having three leaflets arising from the same point (Leaves trifoliolate), leaflets ovate to orbicular, 3 cm long and 1.3-2 cm broad, shortly acuminate and finely pubescent.  Centro is a perennial herb that can reach a height of 45 cm (18 inches). The root system can reach up to 30 cm in depth, Stems grow and branch rapidly, producing a dense mass of branches and leaves on the soil. Stems do not become woody until about 18 months after planting. Leaves are trifoliate, with elliptical leaflets approximately 4 × 3.5 cm (1.6 × 1.4 inches), dark-green and glabrous above but whitish and densely tomentose below. Fruit is a flat, long, dark brown pod 7.5–15 cm (3–6 inches) long, containing up to 20 seeds.

1.3.3  Habitats/ Environmental Adaptation

C. pubescens grows well in soils without fertilizer if it adapts to the environment. For optimal yields, it is best to grow C. pubescens in wet and humid soils, but it can grow in any soil type from sandy to clay soil depending on its location. C. pubescens grows best in a soil pH between 4.9 – 5.5, but will still survive in soils with a pH as low as 4. This plant is also able to endure soils with a high level of manganese.

The growing season for Centro ranges between 4–8 months, but the seeds typically mature within 4–6 months. Centro has versatile rainfall requirements, with its optimal range between 1500–1700 mm, but can still grow with a minimum of 800 mm and can withstand 3–4 month dry periods.

This plant can be cultivated in regions with rainfall ranging from 1000 mm to 1750 mm per year. However, it has a reasonable drought tolerance thanks to its deep root system, so it can take up water from a significant depth. It grows well in nutrient-poor soils.    

A typical seed planting depth is 2.5–5 cm. The shallower depth is used when the soil moisture is appropriate, but when the soil is dry the seed should be planted deeper to reach moisture.

In general, well-drained soils of medium to high fertility but some germplasm is also adapted to acid soils of somewhat lower fertility;  some tolerance of water-logging. Most productive under high rainfall conditions (>1,500 mm/year), but because of its taproot system, able to persist also under dry-subhumid conditions with 3-5 dry months. Warm-season growth only. Shade-tolerant can persist under 80% shade.

1.3.4  Distribution

Native to sub-humid and humid regions of Central America and northern South America. Now naturalized also in tropical Africa and Asia.

1.3.5  Economic Importance/Uses

Centrosema pubescens is widely used as forage and a source of protein to grazing cattle from southern Mexico to Colombia. In the nineteenth century, it was cropped in Indonesia and the Malay Peninsula. It is well adapted to tropical conditions and altitudes below 600 m from sea level.  Centrosema pubescens is grown as a cover crop because it naturally suppresses weeds and is very tolerant to drought. Centro is unable to tolerate cold temperatures but has very low soil and rainfall requirements. This plant is not suitable for human consumption but provides benefits through soil fertility and animal health.

Centrosema pubescens is a promising forage in regions looking for an alternative to enhance the protein content of livestock feed. It is easy to manage and improves soil nitrogen levels. It does not require any special technology or equipment to plant.

Centrosema pubescens can be intercropped with grasses, thus increasing the protein of the cattle diet. The leaves can also be used as a cheap source of protein for broiler chickens. It is a good source of calcium and potassium for animals.

dormancy and seed germination of plant

1.4      Clitoria Ternatea

1.4.1  Botany

Clitoria ternatea plant is named rather bluntly after the clitoris because the deep blue flowers resemble the shape. The most common English name is butterfly pea. The most widely known species of the genus is Clitoria ternatea also known as butterfly pea. The scientific classification of Clitoria ternatea is given below.

Taxonomical Classification

Kingdom:        Angiosperm

(Unranked):     Eudicots

(Unranked):     Rosids

Order:              Fabales

Family:            Fabaceae

Genus:             Clitoria

Species:           C. Ternatea

Binomial name: Clitoria ternatea

1.4.2  Habit

The Clitoria ternatea L. (Blue and white variety) is an ornamental perennial climber with conspicuous blue or white flowers; it is commonly called ‘Gokarn’ English Butterfly Bean. C. ternatea is a vigorous, strongly persistent, stems fine twining, sparsely pubescent, suberect at the base, 0.5-3 m long.  The butterfly pea is a 90 to 162 cm tall, long-lived perennial herb with erect habit. Its flowers are blue and flat, 6-12 cm long similar to those of beans. The thick horizontal root may grow to more than 2 cm long. The leathery leaves consist of three to five leaflets. Leaves pinnate with 5 or 7 leaflets;  petioles 1.5-3 cm long;  stipules persistent, narrowly triangular, 1-6 mm long, subulate, prominently 3-nerved;  rachis 1-7 cm long;  stipels filiform, to 2 mm long;  leaflets elliptic, ovate or nearly orbicular, 1.5-5 cm long, 0.3-3 cm wide, with apex acute or rounded, often notched, and base cuneate or rounded, both surfaces sparsely appressed pubescent.  Flowers axillary, single or paired; color ranges from white, mauve, light blue to dark blue;  pedicles 4-9 mm long, twisted through 180º so that the standard is inverted.  Bracteoles persistent, broadly ovate or rounded, 4-12 mm long.  Calyx 1.7-2.2 cm long with a few fine hairs;  tube campanulate, 0.8-1.2 cm long;  lobes triangular or oblong, 0.7-1 cm long, acute or acuminateStandard obovate, funnel-shaped, 2-5.5 cm long, 2-4 cm wide, notched or rounded at apex, blue with a pale yellow base, or entirely white, a few fine hairs at apex. Pods linearoblong, flattened, 4-13 cm long, 0.8-1.2 cm wide, with margins thickened, and style persistent, sparsely pubescent when mature, pale brown, dehiscent when dry.  Seeds 8-11/pod, oblong, somewhat flattened, 4.5-7 mm long, 3-4 mm wide, olive-brown to almost black, shiny, often mottled, minutely pitted;  23,000 seeds/kg.

Morphology can vary with different growing conditions, which have no significant distinguishing morphological characters, which are normally towards the upper end of the size ranges of descriptions in the taxonomic literature.

1.4.3  Habitat/ Environmental Adaptation 

Clitoria ternatea is commonly found by waysides, thickets, scrub jungles. It is widely cultivated in the tropics.

1.4.4    Distribution

This plant is native to Nigeria, South Africa, Mozambique, Guinea, Ivory Coast, Ghana, Cameroon, Benin, Chad, Kenya, Mali, Malawi, Togo, Uganda, Zambia, Zimbabwe, Tanzania, Ethiopia, Burundi, Somalia, Senegal, Angola, Cabinda, ETC. India Ocean: Mauritius

1.4.4    Economic Values/Uses

Leaves of this plant have been used traditionally to treat urinary troubles, eye swelling, night blindness, scabies, dropsy, antipyretic and skin diseases, etc. Many of the medicinal values are evaluated by many workers such as Anti-diabetic, Anti-compulsive, Anti-bacterial, Hepatoprotective Antihelmintic, and many more.

In Southeast Asia, flowers are used to color food. In Malay cooking, an aqueous extract is used to colour glutinous rice for kuih ketan (also known as pulut tai tai in Peranakan/Nyonya cooking) and in Nyonya chang. In Kelantan, it is used to colour white rice for Nasi kerabu. In Thailand, a syrupy blue drink is made called nam dok anchan, it is sometimes consumed with a drop of sweet lime juice to increase acidity and turn the juice into pink-purple. In Burmese and Thai cuisine the flowers are also dipped in batter and fried.

It is a highly palatable forage legume, generally preferred by livestock over other legumes. It is well known medicinal plant used by many herbal practitioners to treat many diseases. Almost all parts of this plant are reported to have medicinal properties.

In traditional Ayurvedic medicine, it has been used for centuries as a memory enhancer, nootropic, antistress, anxiolytic, antidepressant, anticonvulsant, tranquilizing, and sedative agent. It was used traditionally in an attempt to treat sexual ailments, like infertility and gonorrhea, to control menstrual discharge, and also as an aphrodisiac. In animal tests, the methanolic extract of Clitoria ternatea roots demonstrated nootropic, anxiolytic, antidepressant, anticonvulsant and antistress activity. The active constituents include tannins, resins, starch, taraxerol, and taraxerone.

dormancy and seed germination of plant

1.5      Aim and Objectives

1.5.1  Aim

To determine the efficiency of some physical, chemicals, and hormonal treatments in breaking seed dormancy of Sesbania sesban, Sesbania rostrata, Centrosema pubescens, and Clitoria ternatea.

1.5.2  Objectives

To provide useful information to botanists and agriculturists and others on the methods enhancing seed germination and propagation because of their enormous socio-economic, medicinal potentials.

CHAPTER TWO

Literature Review

2.1      Seed Germination

By definition, germination incorporates those events that commence with the uptake of water by the quiescent dry seed and terminate with the elongation of the embryonic axis (Bewley and Black, 1994). Seed germination is a mechanism, in which morphological and physiological alterations result in the activation of the embryo. Before germination, the seed imbibes water, resulting in the expansion and elongation of the seed embryo. When the radicle has protruded from the covering seed layers, the process of seed germination is said to be completed (Hermann et al., 2007).

Seed germination is controlled by several mechanisms and is necessary for the growth and development of the embryo, resulting in the eventual production of a new plant. Under unfavorable conditions, seeds may become dormant (secondary dormancy) to maintain their germination ability. However, when the conditions are favorable seeds can germinate.

The visible sign that germination is complete is usually the penetration of the structures surrounding the embryo by the radicle; the result is often called visible germination. Virtually the cellular and metabolic events that are known to occur before the completion of germination of non-dormant seeds also occur in imbibed dormant seeds; indeed, the metabolic activities of the latter are frequently only subtly different from those of the former. Hence, a dormant seed may achieve virtually all of the metabolic steps required to complete germination, yet for some unknown reason, the embryonic axis (i.e., the radicle) fails to elongate. By affecting hormonal balance in the seed, environmental parameters including salinity, acidity, temperature, and light, can influence seed germination (Ali-Rachedi et al., 2004; Alboresi et al., 2006).

2.1.2  Germination Process

Germination commences with the uptake of water by imbibition of the dry seed, followed by embryo expansion. This usually culminates in rupture of the covering layers and emergence of the radicle, generally considered as the completion of the germination process. Radicle protrusion after seed germination depends on embryo growth driven by water uptake. The uptake of water by seed is triphasic, with a rapid initial uptake (phase I, i.e. imbibition) followed by a plateau phase (phase II). A further increase in water uptake (phase III) occurs only when germination is completed, as the embryo axis elongates and breaks through its covering structures (Schopfer and Plachy, 1984; Bewley, 1997b; Manz et al., 2005). Cell elongation is necessary, and is generally accepted to be sufficient, for the completion of radicle protrusion; cell division is not essential (Barroco et al., 2005).

The following processes noted below have been reported during germination, namely:

  • Imbibition of water: The first step in the process of seed germination is imbibition or absorption of water. The seed takes in water through the micropyle which results in swelling of the seed. Imbibitions may be defined as a physical process in which living or dead plant materials take up water or liquid mainly by adsorption due to the presence of hydrophilic or lyophilic colloids inside them through the submicroscopic capillaries present on the general surface of the body.
  • Hydration and enzymes activation: hydration of seed causes formation or activation of various enzymes systems. In the process of germination, numerous enzymes like lipases, proteinases, hydrolases, phosphatases, etc. are either activated or de novo synthesized. It is evidenced that the plant growth regulators affect the synthesis or activation of some of these enzymes.
  • Breakdown of reserve material in the seed by the enzymes.
  • Transport of breakdown products from the nutritive tissue to the embryo.
  • Synthesis of new material from breakdown products. Carbohydrates, Fats, and Proteins are digested to products ATP (adenosine triphosphate) which is converted to ADP (adenosine diphosphate) to release energy for biological activities.

2.1.3  Conditions Necessary for Germination

Seed germination is affected by various environmental conditions.

Various environmental factors, such as light and temperature (Chauhan & Johnson, 2010) affect seed germination and dormancy. Temperature and light play critical roles in regulating seed germination (Chauhan et al; 2006a). A non-optimal temperature could result in the inhibition of germination and ultimately in the induction of dormancy (Toorop et al; 2011). Light can induce dormancy in positively photoblastic seeds when those seeds are sown in the soil (Toorop et al; 2008).  Before a seed can germinate a set of stages must be completed, including the availability of food stores in the seed. Such food stores include starch, protein, lipid, and nutrients, which become available to the seed embryo through the activity of specific enzymes and pathways (Miransari and Smith, 2009).

  • Temperature Effect

The plants growing in the different regions require different temperatures for growth.

Temperature: is another important factor in regulating seed germination. The temperature of the soil is significantly higher with the maximum variation occurring at the soil surface. This pattern leads to a daily fluctuation that can accelerate germination and modify the response of light-sensitive species. According to Labouriau and Pacheco (1978), the effects of the temperature can be evaluated from changes in the percentage, velocity, and relative frequency of germination during the incubation time. Seeds from different species require alternating temperatures to optimize germination. This necessity most probably reflects an adaptation to the natural fluctuation of the habitat or may be associated with the dormancy process. Whatever the cause, this requirement can confer, in most cases, an adaptive advantage for the species. (Borges and Reindeer., 1993; Copeland and McDonald, 1995).

  • Water

Water is an important factor for growth. In its presence various physiological activities like water absorption, translocation of food materials, activation of enzymes and protoplasm, etc. take place.

  • Aeration (O2)

Oxygen is necessary for respiration during which the food material is oxidized to release energy. “Siegel, S .M; Rosen, L.A (1962) Oxygen is required by the germinating seed for metabolism”. “Oxygen is used in aerobic respiration, the main source of the seedling’s energy until it grows leaves, Raven, Peter H; Ray F. Evert; Susan E Eichhorn (2005)”. Oxygen is an atmospheric gas that is found in soil pore spaces, if a seed is buried too deeply within the soil or the soil is waterlogged, the seed can be oxygen-starved. Some seeds have impermeable seed coats that prevent oxygen from entering the seed, causing a type of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange and water uptake from the environment.

  • Light

“Crocker (1930) well recognized that in most species, light is a critical factor in controlling germination”. The seeds in which germination is favored by light are called photoblastic. Exposure to light breaks down the germination inhibitors in some types of seeds, particularly wildflowers that produce small seeds.

Many seeds have a light requirement for germination, which may involve only a brief exposure, as in the case of lettuce, an intermittent treatment (e.g., succulents of the genus Kalanchoe), or even a specific photoperiod involving short or long days. Phytochrome is the main sensor for light-regulated seed germination. Interestingly, all light-requiring seeds exhibit seed coat dormancy, and removal of the outer tissues of the seed allows the embryo to germinate in the absence of light. The effect that light has on the embryo is thus to enable the radicle to penetrate the seed coat. This penetration often involves some enzymatic weakening of the enclosing tissues.

2.2                  Dormancy

“Despite the fact that many researchers study dormancy, there is no unambiguous definition of the phenomenon, perhaps because it is manifest and broken in different ways in different species (Bewley and Black, 1994; Vleeshouwers et al., 1995;)”. For the sake of simplicity, seed dormancy is regarded here as the failure of an intact viable seed to germinate under favorable conditions. The seeds of some species are prevented from completing germination because the embryo is constrained by its surrounding structures. This phenomenon is known as coat-enhanced dormancy; embryos isolated from these seeds are not dormant. In other species, the second category of dormancy is found in which the embryos themselves are dormant (embryo dormancy).

Seed dormancy could be considered as a block to the completion of germination of an intact viable seed under favourable conditions. (Finch-Savage and Leubner- Metzger, 2006).

However, Quinliven, (1971) and Quinliven and Nichol, (1971) noted that dormancy should not be confused with seed coat dormancy, external dormancy, or hard sidedness, which is caused by the presence of a hard seed covering that prevents water and oxygen from reaching and activating the embryo. It is a physical barrier to germination, not a true form of dormancy.

It is worthwhile pondering why so little progress has been made toward understanding dormancy. Undoubtedly, one contributing factor is that we do not know all the defining events in germination, e.g for seeds with coat-enhanced dormancy, the use of isolated embryos is unsatisfactory because they are no longer dormant. Some interesting observations have been made using isolated dormant embryos, but again, these are composed of several tissue types; moreover, the cellular bases for the imposition and breaking off their dormancy may be different from those for seeds with coat enhanced dormancy.

2.3      Effect Of Chemical Treatments

This challenge of seed coat imposed dormancy has also been demonstrated by other members of the Acacia generic name; Acacia tortilis (Forsk), Acacia Seyal (Del), and Acacia nilotica (L) (Msanga, 1998; Albrecht, 1993).

Acid scarification is another method of physical scarification that has been found valuable in the breaking of seed dormancy during plantation establishment (Gonçalves et al., 2011; Pipinis et al., 2011). In other words, the use of acid scarification and exposure time in breaking seed dormancy in A.auriculiformis is poorly documented.

Reports of earlier works on Enterolobium cyclocarpum (Agboola and Adedire, 1998) Piliostigma reticulatum (Aduradola, 1999), and Adansonia digitata (Adio et al., 2006) found that treatment with acid significantly promoted germination of the species seeds. The observed significant differences indicated that acid treatment of seeds stimulated prompt and uniform germination.

  • Sulphuric Acid H2SO4

Agbogidi et al. (2007) noted that soaking of Dacryodes edulis seeds in concentrated

H2SO4 reduced the germination period considerably and concluded that it was the best method, though, dangerous to handling.

Chemical scarification with concentrated H2SO4 was potent in breaking seed dormancy of Gmelina arborea Mensah and Agbagwa (2004)

Some researchers indicated the positive effect of concentrated Sulphuric acid (H2SO4) for one until two hours for scarification of a hard coat of honey locust and stratification did not affect seed germination.

Fordham (1996) in studying on seed germination of some leguminous species, found a seed of Honey locust required relatively long periods of sulphuric acid two and half hours pretreatment, the seed of Albizia julibrissin need two hours time pretreatment with sulphuric acid to the effect of rapid general germination.

  • Hydrogen peroxide H2O2

It has been known for long that pretreatment of seeds with oxidants such as H2O2 (in a dose-dependent manner) leads to breaking, primary seed dormancy (Jann and Amen, 1977), secondary dormancy provoked by salinity, high-temperature stresses (Kürsat and Kabar, 2010), or dormancy due to presence of germination inhibitors (Ogawa and Masaki, 2001). Hydrogen peroxide has been known to function as a stress signal in plants (Hung et al., 2005) and hence exogenously applied H2O2 in a dose-dependent manner has been reported to ameliorate seed germination in many crops (Patade et al., 2012; Gregario et al.,2010; Liheng et al., 2009; Azevedo et al., 2005). However, in cotton, Saeed (1974) reported that other than enhancing the germination rate, H2O2 pre-treatment of seeds neither increased the germination percentage nor the root length. There is limited information available on the role of H2O2 in cottonseed germination.

  • Potassium Nitrate KNO3

In many garden plants, potassium nitrate breaks seed dormancy and increases healthy seedlings. Potassium nitrate increases the level of oxygen by decreasing the oxygen available for citric acid cycle (Bewley and Black., 1994). L. latifolium seeds were released from physical dormancy in different concentrations of KNO3, other research has shown that nitrogenous compounds play a regulatory role in breaking seed dormancy in some plant species (Bethke et al., 2004; Rouhi et al., 2010.

  • Ethanol 99%

Alcohol stimulates germination in hard coat seeds, particularly those of the Fabaceae by softening the waxy seeds coat thereby allowing the inflow of water and gaseous exchange. Ethanol has been reported to have a stimulatory effect on the germination of seeds of many plant species Taylorson and Hendricks, (1979); Bewley and Black, (1982). Stimulation of the germination of caryopses by ethanol was reported in Panicum dichotomiflorum, Taylorson, and Hendricks, (1979), different mechanisms by which ethanol might break dormancy have been reported.

Ethanol might accelerate germination by promoting the uptake of oxygen ( Adkins et al., 1984).

It was suggested that ethanol might break dormancy by promoting the Kerbs cycle and glycolysis (Adkine et al., 1984; Corbineau et al., 1991).

  • Methanol 99%

Alcohol pretreatment has been reported to be effective in the breaking of dormancy and improvement of germination in seeds, particularly those of Fabaceae (Etejere et al., 1982).

Methanol (methyl alcohol) has been reported to stimulate seed germination and biomass accumulation in a number of plant species and may act as the Carbon source for these plants (Rowe et al.,1994; Morales-Payan and Santos,1997).Studies with soybeans and cottonseeds how that methanol mimics the effects of weathering,

Stimulated or accelerated aging, and maybe a useful screening tool for evaluating seed quality and seedling performance.

Methanol absorbed in the plant, rapidly metabolized to CO2 in plant tissue due to the smaller size of methanol rather than CO2 (Morales-Payan and Santos, 1997).

2.4      Effect Of Hot Water On Seed Germination And Dormancy

“Iliamna remota seeds are dormant and may require treatment to break dormancy. Without seed pretreatment, only a few I. remote seeds germinated (McDonnell, pers. obs.)”. “However, when seeds were exposed to cold moist stratification (Flood et al. 2000), scarification (Swinehart and Jacobs 1998, Wadmond 1932), and hot water (Wadmond 1932, Hilscher and Preece 1994, McDonnell et al. 2006), higher seed germination than controls resulted”.

2.5      Effect Of Hormonal Treatment

  • Gibberellin Acid

Plant hormones can affect different plant activities including seed dormancy and germination. Gibberellic acid (GA3) is the most common hormone to accelerate the breaking of dormancy (Rogis et al. 2004; Chauhan et al. 2006a; Gashi et al. 2012).

GA is intimately associated with the release of dormancy of seeds of many species. For many species, soaking the seed in a solution of GA can overcome dormancy and jump-start germination. Higher germination percentage, faster and more uniform germination of treated seeds is possible.

One notable exception where GA enhances germination where they looked at the germination of difficult to germinate species and obtain better germination with GA3 treatment, however, GA is used to enhance fruit and seed.

Tang et al. (2012) found that exogenous GA3 applications promoted higher germination in annual bluegrass (Poa annua), Meadow foxtail (Alopecurus aequalis), and Alaska chickweed (Stellaria aquatic).

Plant hormones can affect different plant activities including seed dormancy and germination (Graeberet et al., 2012). Gibberellic acid (GA3) is the most widely used PGR to improve seed germination in different plant species (Bao & Zhang, 2011; Shen et al., 2012). For example, long ago apple and peach seed germination was reported to be enhanced by the application of GA3 (Rouskas et al., 1980; Mehanna et al., 1985). Gibberellins can activate dormant seeds, although the hormone does not control seed dormancy (Bewley, 1997; Miransari and Smith, 2009). GAs plays a key role in dormancy release and the promotion of germination.

In addition, growth regulators such as gibberellic acid (GA3) can induce seed germination without after-ripening in plants (Bewley & Black 1994).

  • Cytokinin

Cytokinin has been shown to have stimulatory effects on the germination of seeds of a wide range of plant species (Jones and Stoddart, 1977; Thomas, 1997; Miyoshi and Mii, 1995).

Cytokinin was reported to have a slightly promotive effect on the germination of intact seeds of cultivated rice (Roberts, 1963). It also stimulated the germination of dehusked, but not of intact seeds of dormant red rice (Cohn and Butera, 1982).

2.6      Seed Coat/ Anatomy Effect

The seed covering helps to impose dormancy in seeds. The seed coat which includes pericarp, testa, etc, may act as a hindrance to the seed, which may be hard for oxygen and water to penetrate.

In this case, seeds can be classified as being hard or dormant. Some members of legumes is said to be in the category of hard seediness (Harrington, 1916). The seed coat is one of the problems that causes dormancy, which prevents germination to take place.

Some water-permeable seeds are impermeable to gases. Dormancy can be made easier by the treatment that can soften the hard coat, crack, or prick the hard seed coat, which can imitate the soften of the hard coat or covering it with chemicals like hydrogen peroxide, sulphuric acid, etc.

Furthermore, taxonomically related species often share the same type of dormancy, most species of the Fabaceae exhibit physical dormancy caused by advanced morphological structures of the seed coat. The seed coats consist of four distinct layers which are: the cuticle, the macrosclereids, osteosclereids, and the parenchyma layer (Schmidt, 2000). The cuticle is the outer layer that has a waxy and water-repellent character. Macrosclereids or palisade vertical cells. Osteosclereids is a layer of more loosely packed cells and the parenchyma layer is made up of little differentiated cells.

CHAPTER THREE

Materials And Methods

3.1     Experimental Site

“The experiment was conducted at the Centre for Ecological Studies of the University of Port Harcourt, Rivers State, Nigeria”.

3.2       Sources Of   Materials:

            “Matured seeds were collected from IITA Ibadan; the seeds are Centrosema pubesecens, sesbania sesban, sesbania rostrata, and clitoria ternatea”. “The seeds were harvested in 2014 and the experiment started in October 2014”. “The seeds were stored in the refrigerator.   

Petri dishes and chemicals namely: Potassium nitrate (KNO3), Hydrogen peroxide (H2O2), Sulphuric acid (H2SO4), Ethanol (C2H5OH), and Methanol (CH3OH) were from Joechem chemical shop, Choba junction, Port Harcourt, Rivers State”.

3.3      Methods

  • Viability Test Carried Out By Flotation Method

The viability test of the seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea was determined by the floating method. The viable seeds settled at the bottom while the others floated (non-viable or dead seeds) to the top. The seeds that settled at the bottom of the container were used for the experiments.

  • Determination of Water Uptake

Seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were properly cleaned with cottonwood to remove dirt and were weighed on an analytical weighing balance, after weighing, the different seeds were poured into different beakers and 10 ml of distilled water was added and then incubated for intervals of 1 h, 4 h, 8 h, 24 h and 48 h after which the moist content was determined.

Germination Procedures

Each treatment was replicated five (5) times with ten (10) seeds per petri dish. Each petri dish was lined with 9 mm Whatman filter paper, moistened with 5 ml of distilled water or the required chemicals/ hormone solution, and germinated at 25 oC. The Petri dishes were observed daily and moistened when necessary.

Each treatment had a control set up alongside. The experiments were observed daily and germination was recorded when the radicle protrudes through the seed coat. The final germination was recorded after 14 days.

Germination of intact seeds.

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were germinated without any treatment or pre-treatment and treated as described in the germination procedure.  

Soaking in Hot water

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked in hot water for 2 mins, 4 mins, 10 mins, 15 mins, 20 mins, and 30 mins and later transferred to different disposable Petri dishes and treated as described in germination procedure.  

Treatment with H2SO4

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked in H2SO4 for different duration 2 mins, 4 mins, 10 mins, 15 mins, 20 mins, and 30 mins; rinsed under a tap running water and distilled water and transferred to their respective petri dishes and treated as described in germination procedure.  

Treatment with Hydrogen peroxide (H2O2)

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were treated in H2O2 for different duration 2 mins, 4 mins, 10 mins, 15 mins, 20 mins, and 30 mins, and was rinsed under running tap water and later transferred to different disposable petri dishes and treated as described in germination procedure.   

Treatment with 99% Ethanol

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked in Ethanol for 2 mins, 4 mins, 10 mins, 15 mins, 20 mins, and 30 mins and was rinsed under a running tap and later transferred to different disposable petri dishes and treated as described in germination procedure.  

Treatment with 99% Methanol

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked in Methanol for 2, 4, 10, 15, 20, and 30 mins and was rinsed under a running tap and later transferred to different disposable petri dishes and treated as described in germination procedure.  

Treatment with KNO3

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were pre-treated with 2 % KNO3 concentration and placed as described in the germination procedure.  
  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked in water for 24 hrs and germinated in KNO3 in 1 mM, 5 mM, and 10 mMand later transferred to different disposable petri dishes and treated as described in germination procedure.  
  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked in KNO3 for 24 hrs and germinated in KNO3 in 1 mM, 5 mM, 10 mM, and100 mM and later transferred to different disposable petri dishes and treated as described in germination procedure.  
  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked in KNO3 for 24 hrs and germinated in water in 1 mM, 5 mM, 10 mM, and100 mM and later transferred to different disposable petri dishes and treated as described in germination procedure. 

Treatment with GA3

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked inGA3 for 24 h and germinated with water, and treated as described in the germination procedure.  
  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were germinated in GA3 and treated as described in the germination procedure.  
  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea weresoaked inwater for 24 h and germinated in GA3, and treated as described in the germination procedure. 

Treatment with Kinetin

  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were germinated in kinetin and treated as described in the germination procedure.  
  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked inkinetin for 24 h and germinated in water, and treated as described in the germination procedure.  
  • Intact seeds of Centrosema pubescens, Sesbania sesban, Sesbania rostrata, and Clitoria ternatea were soaked inwater for 24 h and germinated in kinetin and treated as described in the germination procedure.   

Seed Coat Analysis

 Dry seeds for the experiment were collected from IITA, fixed in FAA (formalin, acetic acid, and alcohol) for 12 hrs. Thereafter, the specimens were dehydrated in a series of different percentages of ethanol (30 % and 50 %) and stored in 70 % ethanol and sectioned (Agbagwa, et al., 2007). The sections were stained in 1 % Safranin red for two minutes, counter-stained with Alcian blue, mounted on a slide, viewed, and photographed with Optika B-1000 FL LED microscope.

CHAPTER FOUR

Results/ Discussion

A         Sesbania sesban

4.1      Germination

            The result of the intact seeds of sesbania sesban germinated at 25 oC in the dark and light condition gave 0 % germination after 14 days of incubation under laboratory conditions.

Also, germination of intact seeds under field conditions gave 0 % germination. The results indicated that the intact seeds of Sesbania sesban are dormant and do not germinate under natural conditions.

4.2      Water Absorption

The result of the water uptake of intact seeds of Sesbania sesban, Sesbania rostrata, Clitoria ternatea, and Centrosema pubescens is shown in figure 4.2.0 a

The water absorption capacity was determined using the McWatters et al., 2002 method

equation (5)

Where, Wa is water absorption (d.b. %), Wf is the weight of seeds after immersion (g) and Wi is the weight of seed before immersion (g).

dormancy and seed germination of plant

Figure 4.2.0a

PY; sensu Baskin and Baskin, 2004, stated that seeds with a water-impermeable seed coat have physical dormancy and such seeds occur in 16 families of angiosperms (Baskin et al 2000). Baskin et al ., 2000 stated that in all cases, PY is associated with water-impermeable layers of macrosclereids. The water imbibition of the seed of Sesbania rostrata was from 0.51 to 70.91, Sesbania sesban gave 2.45 to 25.4, Centrosema pubescens gave 8.02 to 35.8, and Clitoria ternatea recorded0.9 to 86.36.

4.3.1  Hot Water Pretreatment

dormancy and seed germination of plant

 Figure 4.3.1a: Shows the effect of hot water treatment on the germination of intact seeds of Sesbania sesban.

Pretreatment of intact seeds in hot water for 2 mins before incubation gave the highest germination (28 %) when compared to the control (0 %) and other treatments. Percentage germinations decreased with a further periods of immersions (4 mins to 30 mins), with 20 and 30 mins of immersion giving the lowest germination of 8 %. Generally, the results indicate enhancement of germination when intact seeds are pretreated in hot water when compared to control. Hot water pretreatment has been reported to improve germination in the seeds of T.indica by Muhammad and Amusa 2003, and this finding supports my results that showed promotion of germination of Sesbania sesban when pretreated with hot water. The decrease in germination could be attributed to the reduction of the temperature of the water with time. The mechanisms of the hot water effect might be the softening or loosening of seed coat integrity and structure, thus allowing the entry of water and diffusion of oxygen into the seed to permit germination.

Means with the same letter are not significantly different.

dormancy and seed germination of plant

Figure 4.3.1b: Shows the effect of H2SO4 treatment on the germination of intact seeds of Sesbania sesban.

The results showed a gradual increase in percentage germination from 2 mins immersion (28 %) to 15 mins immersion (54 %) and then decreased slightly from 20 mins (52 %) to 30 mins (48 %). These results are higher than the control which gave 0 %, 15 mins gave the highest percentage (54 %). H2SO4  has been used by several workers to break seed dormancy of Gmelina arborea byMensah and Agbagwa (2004).

Means with the same letter are not significantly different.

dormancy and seed germination of plant

Figure 4.3.1c: shows the effect of hydrogen peroxide (H2O2) pretreatment on the percentage germination of intact seeds of Sesbania sesban.

The percentage germination of H2O2 pretreatments were 0 mins – 0 %, 2 mins -56 %, 4 mins- 56 %, 10 mins – 58 %, 15 mins – 60 %, 20 mins – 44 %  and 30 mins – 34 %, 15 mins pretreatment gave the highest germination while the 30 mins gave the lowest. These results were higher than the control treatment.  Hydrogen peroxide increases germination in the pea seeds by Gregorio et al. 2012.

Means with the same letter are not significantly different.

dormancy and seed germination of plant

Figure 4.3.1d: shows the effect of 99 % Ethanol pretreatment on the percentage germination of intact seeds of Sesbania sesban.

Germination showed a progressive increase from 2 mins (16 %) immersion to 30 mins immersion (56 %) while the control gave 0 %. Ethanol has been reported to have stimulatory effects on the germination of seeds of many plant species (Taylorson and Hendricks, 1979; Bewley and Black, 1982; Ikeda, 1963). Means with the same letter are not significantly different.

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