M.Sc Thesis by Uchenna Charles Njimogu.
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.
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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
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.
Species: S. seban
Sesbania sesban L.
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).
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).
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).
1.2 Sesbania Rostrata
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.
Species: S. rostrata
Binomial name: Sesbania rostrata
Source: Bremek and Oberm
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.
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.
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.
Table 2.0 Species distribution of Sesbania in various regions of the world.
|Region||No. of species||Source|
1.3 Centrosema Pubescens
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.
Sub tribe: Clitoriinae
Species: C. pubescens
Binomial name: Centrosema pubescens
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.
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.