Actually the Genus name I'm talking about is Garcinia, i.e. the Garcinia kola, which is called the Bitter Cola. I'm not talking about Cola sp., and both papers I quote, they all refer to Garcinia kola, not gotu kola (as in Centella asiatica).
The main confusion rises in the comparative study of the paper #1 and the paper #2 as follows:
#1 paper says: "Germination percentage was low for Garcinia kola because of its dormancy and impenetrable seed coat."
#2 paper says: "The thin leathery seed cover is not a barrier to water penetration in the embryo, however, decoating or ethanol treatments (soaking in 70% ethanol solution for 1 to 2 hours) can increase germination to >90% after c. 5 months."
If the the thin seed coat is not a barrier to water penetration in the embryo, then what's the point of decoating, or nicking?
Here's the #1 paper I'm referring to (from the World Agroforestry):
ENHANCING GERMINATION OF BITTER COLA (GARCINIA KOLA) HECKEL: PROSPECTS FOR AGROFORESTRY FARMERS IN THE NIGER DELTA
P. O. Anegbeh, C. Iruka, and C. Nkirika
World Agroforestry Centre (ICRAF), International Institute of Tropical Agriculture (IITA)
IITA High Rainfall Station, Onne, P. M. B. 008, Nchia-Eleme, Rivers State, Nigeria
Email: [email protected]
or [email protected]
The study on enhancing germination of Garcinia kola was conducted using 5 pre-treatments. These included soaking seeds in cold water for 96, 72, and 48 hours for treatments 1, 2, and 3 respectively, cutting seeds at the opposite end to the radicle with kitchen knife (nicking) for treatment 4 and control treatment (untreated seeds for treatment 5). The aim of this study was to determine the best pre-treatment for optimum germination of Garcinia kola “seed”. Germination tests were carried out after pre-treatments for 10 months using one hundred seeds for each treatment in ICRAF nursery established at IITA station in Onne, Niger Delta Region of Nigeria. The result showed that seed cutting (nicking) was the most suitable pre-sowing treatment to increase seed germination of Garcinia kola. In the first 6 weeks of testing, germination did not occur in all the treatments. From the seventh week, germination commenced in treatments 1 and 4. Whereas treating the seeds with mechanical scarification (nicking) significantly (P<0.05) enhanced germination of Garcinia kola, seed germination was also significantly (P<0.05) improved, at least for up to 33 weeks, by soaking the seeds in cold water for 96 hours. The wide variation in germination percentage, germination rate and germination speed of G. kola depended on dormancy that was overcome by seed treatments prior to sowing.
Key words: bitter cola, Garcinia kola, germination, scarification.
Garcinia kola Heckel, often called bitter kola, is an indigenous medicinal tree belonging to the family Guttiferae. Morphologically, Garcinia kola resembles Allanblackia floribunda. It is well branched, evergreen, and grown as a medium size tree, reaching 12 m high in 12 years, and found in moist forests throughout West and Central Africa. Garcinia kola has regular fruiting cycle and the tree produces fruits every year. The species is one of the most important trees valued in Nigeria for its medicinal seeds and its exploitation in the natural forests has been very heavy.
The seeds of G. kola have pharmacological uses in treating coughs, throat infections, bronchitis, hepatitis (inflammation of the liver), liver disorders (Farombi et al., 2005). According to Adegoke et al., (1998), seeds of G. kola have inhibitory effects on lipid peroxidation in rat liver homogenates. The seeds which serve as a bitter stimulant also serve as snake repellent when they are placed round the compound (Nair, 1990; Daily Champion, 2004). Other medicinal uses include: purgative, antiparasitic, antimicrobial. The seeds are used to prevent and relieve colic, cure head or chest colds. The seeds constituents include—biflavonoids, xanthones and benzophenones. The antimicrobial properties of this plant are attributed to the benzophenones, flavanones. This plant has shown bronchodilator effect (Orie and Ekon, 1993), anti-inflammatory, antimicrobial, antibacterial and antiviral properties (Ebana et al., 1991; Akoachere et al., 2004). In laboratory tests, Garcinia kola was found to halt the deadly disease caused by Ebola virus in its tracks. The virus causes Ebola haemorrhagic fever - an often-fatal condition. Compounds from the plant have also proved effective against some strains of flu, a contagious respiratory disease also commonly known as influenza (Iwu, 1993). Its by-products are also useful: the wood makes excellent fuel wood; its dense rounded crown makes it an ideal tree for shade around homestead; the branches are used as chewing stick because of its bitter taste and antibacterial activities of its extracts (Taiwo et al., 1999).
In Nigeria, low populations of G. kola are found in home gardens and few stands are found in the wild due to rapid deforestation and heavy exploitation in the natural forests. These factors seriously depleted the populations of the species. But demand for G. kola is currently very high in Nigeria and though few seeds are available in the markets, production of the species is limited due to problem of seed dormancy. The seeds need to be treated to enhance germination. During a priority setting exercise, Garcinia kola was one of the useful indigenous trees prioritized by farmers in West and Central Africa. For many farmers who practice agroforestry, medicinal and fruit trees turn out to have higher priority. However, it is unlikely that rural farmers would plant G. kola on a large scale because the untreated seeds are difficult to germinate. Discouragingly, farmers believe that germination of G. kola takes about six to twelve months and that only few seeds germinate. They also believe that the tree takes a longer time of about eight to ten years to reach reproductive phase. According to Anegbeh, et al., (2005) early flowering and fruiting of very useful indigenous fruit trees enhance food security and harness rural livelihoods.
The challenges to development institutions are to help overcome these problems and to respond to priorities of rural communities, especially in the area of conserving highly endangered and valued species. Information on improving the germination of G. kola is not available in the Niger Delta Region of Nigeria. Therefore, the objective of this study was to break dormancy and improve germination of G. kola within a short time and make the information available to farmers.
MATERIALS AND METHODS
The study was conducted at the International Institute of Tropical Agriculture (IITA) High Rainfall Station, Onne, Nigeria (40 51' N 70 03' E). The Station receives a mean annual rainfall of 2,400 mm. The soil is an Ultisol derived from coastal sediments. They are strongly acidic (pH 4.4) and of low fertility. They are classified as siliceous, isohyperthermic, typic paleudult. The soil is deep, well drained with good physical properties but chemically poor. Temperature varies from 270 C in February and March (warmest months) to 250 C in July (coolest month). Relative humidity varies from 78% in February (driest month) to 89% in July (rainy month). Sunshine also varies from 2 hrs/day (September) to 6hrs/day (February).
Genetically representative fruit samples were collected in 2000 from trees growing in home gardens at Ilile village (Imo State) and Ibiaku Ikot Edet village (Akwa Ibom State) in the Niger Delta Region of Nigeria to increase genetic diversity. This involved random population sampling of 50 to 100 fruits on an individual tree basis to ensure that selection of a particular tree was not influenced by another tree. Ripe fruits of the trees were collected from all parts of the crown since they might have been pollinated by different pollen sources. The containers used for collecting fruits resulted in an open packing arrangement that gave better flow of air around the fruits and thereby facilitated drying and reduced the hazards of mould and decay. Collecting fallen fruits and seeds was avoided because of uncertainty regarding their source; risks of contamination from morphologically similar seeds of nearby related species; their lower physiological quality; and greater risks of contamination of the fruit with soil-borne pathogenic fungi. The bulked seed lot was thoroughly mixed and transported to ICRAF nursery. The seeds were extracted from the fruits at the nursery , washed in clean water and air dried for one week to ensure viability.
Five treatments were used. Treatments 1, 2 and 3 involved soaking 100 seeds of each treatment in clean cold water at room temperature for periods of 96, 72, and 48 hours respectively. For treatment 4, one hundred seeds were nicked near the micropyle, while 100 untreated seeds were used for the control (treatment 5). Concrete boxes with internal dimension of 1 x 1 m and a depth of 10 cm were constructed, placed in the nursery as germination beds and covered with growth chambers. After treatment, 100 seeds from each treatment were distributed on top of the surface of top-soil without touching each other and then covered with the soil to a uniform depth of 2 cm. Manually, water was applied daily so that the medium was kept moist at all times without getting waterlogged. The treatments, which were replicated 4 times, were arranged in randomized complete block design (RCB) because of heterogeneity in soil, and variability in both the growth chambers and the treatment applied (Wahua, 1999).
Data collection and analysis:
In the nursery, the criterion for germination was a visible protrusion of the shoot apex or epicotyls on the surface of the soil. Germination was recorded daily until no further germination occurred. Data on percentage germination, cumulative germination, complete dormancy period (the number of days from sowing to start of germination), total dormancy period (the number of days from sowing to completion of germination), differential dormancy period (the difference between the total and complete dormancy periods), germination rate (total number of seeds germinated /number of days in the germinator) (Djavanshir and Pourbeik, 1976) and germination speed (number of days required for 50% of the germinating seeds to emerge) were collected. Procedurally, the data were analysed using analysis of variance. Before statistical analysis, data were transformed into arcsin values (cumulative germination) and square root values (dormancy). Means and standard errors were calculated.
Hypogeal germination was found in seeds of Garcinia kola. Treatments studied had profound effects on dormancy periods of G. kola. Results revealed that dormancy periods were significantly (P<0.05) shorter in treatment 4 than the other treatments (Fig. 1.). The reduction in dormancy periods in treatment 4 can be explained by the fact that the seeds were nicked and this enhanced their ability to imbibe water necessary for hydrolysing substances stored in the dormant embryos. It is noteworthy that treatment 4 recorded the shortest total dormancy period, which is the period required for completion of germination. The dormancy in G. kola contributed to the longest periods observed in the untreated seeds of the control (Treatment 5). It appeared that seeds of G. kola restricted water supply and gaseous exchange into the embryos and inhibited germination in the control treatment.
Clearly, treatment 4, nicked seeds, recorded an impressive 100% germination (Fig. 2) in the seeds of this highly endangered valuable agroforestry tree in seven months. The 100% germination recorded for treatment 4 would aid prospect for rural farmers who were initially discouraged by the long periods required for the seeds to germinate. This is also an indication of the remarkable results achieved through the tree domestication efforts of World Agroforestry Centre.
Treatment 4 had the highest germination rate (Fig. 3). Optimum germination rate (100%) was obtained in 7 months for the seeds that were nicked. This germination rate was followed by treatment 3. As expected, treatment 4 gave the fastest germination speed of 12 days (transformed data) for 50% germination (Fig. 4). This was followed by treatment 1 (27 days), treatment 2 (28 days), treatment 3 (28 days). The untreated seeds, in treatment 5, were the slowest as they required 29 days for 50% germination. The results of this study are positive indication of how effective germination can be enhanced in difficult-to-germinate seeds by closely studying the dormancy and germination in G. kola.
Nicking was very effective in enhancing germination of G. kola. Germination percentage was low for G. kola because of its dormancy and impenetrable seed coat. It appears embryos in seeds of G. kola have built-in dormancy mechanism. Nicking seeds of G. kola prior to sowing is a dependable way to speed up germination of G. kola. Earlier workers have shown that mechanical scarification and water are features that enhance germination in seeds of tropical trees (Awodola, 1994; Agboola and Adedire, 1998; Aduradola, 1999). Different storage conditions have been reported to influence germination of Chrysophyllum albidum (Egharevba and Uwadiae, 1995). Esenowo and Adebona (1990) have showed that heat treatment caused some metabolic changes within the dormant seeds of Corypha umbraculifera (L) and enhanced germination. High temperature and high humidity can have negative effect on seed germination. Since the natural regeneration of this species consists of scattered individuals, domestication of Garcinia kola would require improvement in germination and planting by cuttings. The results have greatly helped focus tree domestication activities to specifically address the needs of some rural communities in the Niger Delta Region of Nigeria. Garcinia kola has agroforestry potentials as a wind breaker because it has good canopy. In addition to this potential as a wind breaker species, its hard wood is suitable for tool handles. Rural farmers increasing appreciate good quality G. kola developed by World Agroforestry Centre at IITA station, Onne, Rivers state. The training of farmers and availability of improved planting materials would give farmers in the Niger Delta Region of Nigeria opportunity to improve their health, income generation, and sustainable livelihoods because Garcinia kola provide not only a valuable source of medicine for the rural villagers, but many other useful products and services as well.