In Vivo Stimulation of Axillary Bud Initiation, Growth and Development of Plantain (Musa Aab.) Using Coconut Water and Indole-3-acetic Acid
The study was carried out at the University of Ghana Forest and Horticultural Crops Research Centre (FOHCREC), Kade from 2008 to 2012. Two experiments were conducted to investigate the effects of coconut water (CW) alone or in combination with varying concentrations of auxin (IAA) on axillary bud initiation, growth and development of plantain (cv. Asamienu).
In the first experiment, coconut water from fully matured dried fruits was supplemented with three different IAA concentrations, 10-4 M, 10-3 M, and 10-2 M to produce five different coconut water : IAA ratios (v:v), viz: 8:0, 6:2, 4:4, 2:6, 0:8. Three weeks after the injection treatments, variations were seen in the rate of axillary bud formation and growth. The highest number of well-differentiated axillary buds was produced after injecting with a combination of 2ml coconut water and 6ml 10-2M IAA whilst the highest number of fully developed plantlets was produced with a treatment of 8ml coconut water alone. One month after the application of the bud manipulation technique, the highest number of additional well-differentiated axillary buds and fully developed plantlets was produced with 2ml coconut water plus 6ml 10-2M IAA and 4ml coconut water plus 4ml 10-2M IAA respectively.
In the second experiment, the endogenous content of cytokinin (trans- zeatin riboside) and auxin (IAA) in coconut water from fruits at four different fruit maturity stages: liquid endosperm formation stage (6 months after flowering), solid endosperm formation stage (8 months after flowering), semi matured endosperm stage (10 months after flowering), fully matured dried fruit stage (13 months after flowering) and their effects on the proliferation of axillary bud initiation and development were evaluated. In both experiments, distilled
water was injected as the control. Results of the quantitative analysis of the endogenous content of trans- zeatin riboside and IAA showed major changes at the different fruit maturity stages. The results indicated that as the coconut fruit matured the IAA content in the coconut water decreased while the trans- zeatin riboside content inreased with fruit maturity.
Three weeks after coconut water injection treatments, the highest number of well- differentiated axillary buds was obtained for suckers treated with coconut water from fruits at liquid endosperm formation stage whilst the highest number of fully developed plantlets was produced from treatments with coconut water at semi-endosperm formation stage treatment. One month after the application of the bud manipulation technique, the highest number of additional well-differentiated axillary buds and fully developed plantlets were produced from treatments with coconut water at the liquid endosperm formation stage. Furthermore, treatments with coconut water from fruits at liquid endosperm formation stage produced the highest additional well-differentiated axillary buds one month after the application of the split corm technique whereas the highest additional fully developed plantlets was obtained from treatments with a mixture of coconut water from liquid endosperm formation stage and fully matured dried fruits. In general, treatments with coconut water from fully matured dried fruits produced the largest and the most vigorously growing plantlets.
Plantain (Musa AAB) is an important source of high-calorie energy in the diet of many people of the entire West African sub-region (Stover and Simmonds, 1987). It provides about 70 million people in sub- Saharan Africa with more than 25% of their carbohydrate needs (Swennen, 1990). Plantain is grown across all the humid agro-ecological zones and forms an integral component of most of the complex farming systems (Swennen and Vuylsteke, 1991).
In Ghana, plantain is ranked third after yam and cassava in the food crop sector (FAO, 2006). National production is about 3.6 million metric tonnes per annum (African News Network, 2007) and about 90% of plantains produced is consumed locally (African News Network, 2007). It contributes about 13.1 % of the Agricultural Gross Domestic Product, AGDP (FAO, 2006).
One major challenge in the production of plantain is the lack of large numbers of healthy uniform -sized planting materials (suckers) to plant (Hotsonyame, 1991). Farmers usually plant suckers infected with pests and diseases including nematodes and plantain weevils (Afreh-Nuamah, 1994), banana streak and cucumber mosaic viruses (Osei, 1995). All these diseases and pests are transmitted through infected suckers and adversely affect the growth and yield of plantains. Since there is unrestricted movement of infected plantain
suckers in the country, there is a real danger of epidemics if steps are not taken to produce large numbers of disease and pest free suckers for farmers (Osei, 1995).
In vitro and rapid field multiplication techniques of plantains have been developed to overcome the problem of obtaining many vigorous and uniform suckers free from pest and diseases (Vuylsteke and Swennen, 1992). However, suckers obtained from in vitro techniques are prone to the banana streak virus disease which is known to be integrated in the plantain genome (Dallot et al., 2001). The in vitro techniques again require expensive equipment and expertise that are unavailable to most plantain farmers in Ghana. These challenges call for the development of appropriate and adoptable field techniques for farmers.
An appropriate and inexpensive rapid field multiplication of plantains is the split corm technique. The technique involves paring and splitting plantain corms into smaller pieces and sprouting them in moist sawdust or soil to permit dormant axillary buds to sprout. However, the multiplication ratio of the conventional split corm technique is about 1:4 when a regular sized plantable sucker is used. Again, suckers generated from the technique do not grow as vigorous as sword suckers especially when corms are splitted into more than four pieces (Robinson and Alberts, 1983; Ahiekpor, 1993). It is therefore necessary to develop other approaches to improve the efficiency of the split-corm technique.
Plantain suckers develop from axillary buds pre-formed on the corm. Therefore stimulation of axillary bud formation on plantain corm could possibly increase the multiplication rate of the split corm technique. Osei (2006) showed that axillary bud
formation and development of plantain could maximally be promoted when injected with 8ml coconut water from fully matured dried fruits or 4 ml of 10-2 M benzyl adenine. A multiplication ratio of up to 1: 15 was obtained when 3-month old split-corm derived suckers were used. However, 50% of the plantlets generated from this technique did not survive due to poor root development. In another study, Nyamekye (1999) observed that 10-3 M solution of indole-3-acetic acid (IAA) significantly improved root production of plantain split corms. However, the initial shoot emergence was delayed which could affect time of flowering and hence maturity period. There is therefore the need to develop rapid field multiplication techniques which will produce multiple shoots that can form roots to improve plant survival and growth and will improve root production and at the same time enhance shoot emergence of split corms.
Differentiation of plant tissues into roots, shoots and flowers is referred to as organogenesis in tissue culture. The optimal ratios of cytokinin and auxins are very important during organogenesis (Haq and Dahot, 2007). In in vitro micro-propagation of plantain, high auxin: cytokinin ratios induce root formation whereas low auxin: cytokinin ratios promote shoot formation. Intermediate auxin: cytokinin ratios promote callus formation which may differentiate into root and shoot (Cronauer and Krikorian, 1984).
Coconut water is a natural source of phytohormones such as auxins and cytokinins (Salisbury and Ross, 1985; Yong et al., 2009). Auxin (indole-3-acetic acid, IAA) and cytokinin (trans- zeatin riboside) are the most active phytohormones in coconut water (Yong et al., 2009). Coconut water may contain varying ratios of cytokinins and auxins concentrations at different fruit maturity stages as has been found for many fruits
(Salisbury and Ross, 1985). Generally, the auxin: cytokinin ratio is higher at the early fruit maturity stage while cytokinin: auxin ratio is higher at later stages of fruit maturity (Salisbury and Ross, 1985).
It is therefore possible that by varying the ratios and time of application of coconut water and IAA in plantain plant, the cells may be stimulated to develop into multiple shoots (suckers) and/or roots.
Objective of the study:
The main objective of the study was to apply in vitro micro-propagation principles to develop an efficient rapid field multiplication technique of plantain that will allow for production of many vigorous and uniform growing suckers at a reduced cost.
Specific objectives of this study were to determine:
- The rate of initiation and development of axillary buds of split corm-derived plantain suckers into plantlets after treatment with different ratios of IAA and coconut water (from fully matured dried fruits).
- The rate of initiation and development of axillary buds of split corm-derived plantain suckers into plantlets after treatment with coconut water from fruits at pre-endosperm formation stage, post-endosperm formation stage and fully matured dried
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