The experiment was conducted in the 2015 cropping season at the University of Uyo teaching and research farm, Use Offot in Uyo LGA of Akwa Ibom State to evaluate the morphological characteristics and yield of four cassava genotypes that were treated with Gibberellic Acid (GA3). The experiment was laid out in a randomized complete block design with a split plot arrangement. The main effect was the growth hormones (GA3 application). While the sub treatments were four cassava genotypes. The cassava genotypes used were TMS 98/0505, TMS 30572, TMS 01/1412 and Obubit Okpo. Data collected were plant height, number of functional leaves per plant, number of branches, leaf area, number of tuber per plant, length of tubers, circumference of tubers and root yield(t/ha). Data obtained were subjected to Analysis of Variance (ANOVA) and significant means were compared with least significant difference (LSD) at 5% probability level. Results showed significant differences in growth and yield parameters. Plants treated with gibberellic acid (GA3) sprouted earlier (100%, 100% and 100%) at 2, 3 and 4 weeks after planting (WAP) compared to plants without gibberellic acid (42.25%, 62.5% and 96.25%) respectively. Gibberellic acid (GA3) treated plants produced the highest number of leaves per plant (13.42, 26.40, 74.11, 122.40, 135.60, 159.75 and 174.77) at 1, 2, 3, 4, 5, 6, 7 and 8 months after planting (MAP) respectively while untreated cassava plants had the least number of leaves per plant (11.49, 22.36, 54. 66, 75.13, 98.70, 129.45, 149.84 and 165.44) respectively. Plants treated with gibberellic acid (GA3) also had the highest number of branches per plant (22.66) at 8MAP compared to that (17.77) observed in untreated plot. Plants treated with gibberellic acid (GA3) had the longest tuber (50.22cm) and widest tuber circumference (28.06cm) while untreated plants had (33.44cm) and (23.00cm) respectively. Plants treated with gibberellic acid (GA3) had significant tuber yield (34.30 t/ha) compared to (25.98 t/ha) harvested from untreated plot. The study therefore suggests that application of Gibberellic acid (GA3) could enhance cassava growth and yield. Among the cassava varieties, TMS 01/1412 performed best in all the growth and yield parameters assessed, followed by TMS 98/0505 and TMS 30572 while the least was from Obubit Okpo.
1.1 BACKGROUND OF THE STUDY
Cassava (Manihot esculenta, Crantz) maintains a prominent positive position among tropical crops. It gives high yield under optimum conditions and has little demand for labour. Cassava is one of the most important root crops in the tropics, feeding over 50 million Nigerians with more than 70% of their daily energy requirements (Nnodu et al., 2006). The crop is one of the most dominant and main crop components in crop mixtures in south-eastern Nigeria (Ikeorgu and Iloka, 1994) and it is gradually gaining importance as an industrial crop (Mouneke and Mbah, 2007). Nigeria’s annual production of cassava is estimated at 49 million tonnes (Aba, 2010) while about 90 percent of it is used as food (Awoyinka, 2009). Yet Nigeria, the world’s largest producer of cassava (FAOSTAT, 2010) has not attained self-sufficiency in cassava production as 100 million tonnes of the commodity is required annually to contribute in guaranteeing food security for the nation where about 65 percent are food-insecure, that is, insufficient access to the amount and variety of food for a healthy and productive life (Aba, 2010).
According to Alves, (2002) and FAO, (2004), cassava is typically perceived to be grown by resource poor small farmers. It can be produced with family labour by basic inputs only and low production risk (Nweke, 2005). Cassava grows over a wide range of ecological conditions and is more tolerant to low soil fertility, drought, pest and diseases, (Udoh et al, 2005, Nnodu et al, 2006). Cassava has advantage of being available all year round since it can be left in the ground after maturity for up to three years before harvesting without spoilage. It also has high productivity per unit area of land (30-40t/ha) with minimal inputs.
1.2 ORIGIN AND DISTRIBUTION OF CASSAVA
Cassava originated from North Eastern Brazil and it was introduced into West Africa by the Portuguese explorers in 15th Century. However, the secondary centre of origin is said to be Central Africa (Rogers, 1963), which today is not considered among the World leading cassava producing Countries. After the 16th Century, the species gradually spread through the various regions of Sub-Sahara Africa and the inhabitants of the region then took cassava to Madagascar. From the West Coast of Central America, Spanish Explorers and traders also took cassava to the Philippines, then to South East Asia. Cassava was also introduced to Southern India from East Coast of Central America from where the Dutch introduced it to Indonesia and Pacific Island (Truman, 2009).
Cassava is grown over a wide range of environments, between latitudes 300N and 300S covering a wide range of temperature (25 – 38oC) and rainfall (1000-2500mm), which improves its vegetative growth. Cassava tolerates drought of about 4 to 6 months but does not tolerate water logging (Hahn et al, 1997). Cassava is also cultivated in semi arid ecological zone as a cash crop. Soils suitable for cassava production are mostly ultisol with low to medium humus contents and the crop adapts to well drained soils from sandy loamy, loamy sand to silt with pH of 5.0 -5.8 but is extremely susceptible to excessive flooding.
1.4 ECONOMIC IMPORTANCE OF CASSAVA
Cassava is used for food, livestock feed and industrial materials. About 70% of total cassava produced is processed into a wide range of products, these include chips and flour. The chips are dried and stored or milled into stable forms before storage. Cassava flour is used in preparing varieties of confectionery. In bread making, cassava flour is used as partial substitute to wheat flour without loss of bread quality (Eggleston, 1991).
The production of cereals, especially maize, is not high enough to meet the energy requirements of both humans and livestock. There is considerable potential for using cassava feed rations in local livestock industries. Fresh root also have low value per unit weight, so processing adds value to the crop products (FAO, 2008).
It has also been reported that the use of cassava in the diets of white Fulani herds in Nigeria increased milk production by 22% and also resulted in increased percentages of butter fat, protein and non-fat solids (IITA, 1990).
Cassava is used in the food industry in many preparations, including sauces, gravies, custard powder, baby foods, tapioca, glucose, confectionery and bakery products. It is also used for jelly or thickening agent. It is used extensively in the manufacture of adhesives, dextrins and paste and as filler in the manufacture of paints. In the textile industry, it is used for wrapper sizing, cloth and felt finishing. It is also used in the manufacturing of drugs and ethanol and as bio-fuel. In Akwa Ibom State, cassava tubers are used in the preparation of local foods, such as garri, Tapioca (Edita iwa), baton manioc (Ayanekpang), cassava cake (Akara iwa), fufu and asa iwa (Ekpe, 1998).
Cassava starch is an important industrial raw material. Over 100 cassava starch derivatives (chemically modified starch) have been developed to provide products with the physical and chemical properties required for specific applications. Raw, unmodified cassava starch can be used successfully, and in many instances advantageously, for industrial applications where, maize or potato starches were used (IITA, 1990; Ndirika, 2006).
1.5 JUSTIFICATION OF THE STUDY
Recently, cassava which uses to be a subsistent crop has suddenly become a commercial and industrial crop. Effort has been made by breeders to increase the yield with the release of new improved varieties. However, the demand for cassava still remains high in order to meets its increasing usage in industries and for export. Therefore, the need arises for yield higher than those gotten from improved varieties. Information from literatures indicates that the application of Giberellic acid (GA3) and other plant growth hormones breaks dormancy (Vreugdenhil and Sergeeva, 1999) and increases production of roots (Xu et al., 1998). For cassava, any increase in production of roots respectively means increase in tubers. So the need arose to investigate the effect of Gibberellic acid (GA3) on cassava stems with the intention of producing more roots and consequently high yield tuber.
1.6 OBJECTIVE OF THE STUDY
Thus the objectives of this investigation are
· To evaluate the effects of Gibberellic acid (GA3) on morphological characteristics of cassava
· To evaluate the effect of Gibberellic acid (GA3) on yield of cassava