Banana is one of the most appreciated local fruit in both green and ripe form with over 500ha under production. However, yield of the dual purpose banana (Ollier and Dwarf Cavendish) is low (18 â 22t/ha) (DAS, 2000) due to production under marginal conditions while the highly priced dessert-type Gingeli banana is becoming rare due to its susceptibility to Fusarium oxysporum f.sp. cubense race 1. In this new era of agricultural diversification, banana is one of the crop that is replacing sugarcane, however the availability of quality planting material for intensive plantation remains one of the major constraints. On the other hand, to prevent the wiping out of the Gingeli banana, there was a need to rehabilitate this and other local clones. The project was thus initiated to develop a protocol for rapid mass multiplication of selected clones to make larger population available for plantation. The first part of the project consisted of identification and horticultural characterisation of elite germplasm and the second part involved protocol development for in-vitro multiplication of the selected clones. Horticultural characterisation enabled the local dessert-type banana to be classified into two groups (the âGingeliâ and the âMamoulâ type) based on peel coloration and pulp taste and texture. Preliminary observations also indicated that Gingeli banana was highly susceptible to weevil attack. Protocol development for in-vitro multiplication was carried out through a series of trials based on Completely Randomised Designs. All micropropagation (shoot-tip) was carried out in modified Murashige & Skoog medium. A fast and effective cleaning and disinfection protocol of explant was developed and explant browning was successfully controlled. The study also demonstrated that any plant part (bud, peeper, sucker) could be used as explant although suckers represented handling advantages. For culture initiation, excised explants (3 â 6mm with an average of 5mm) also represented handling advantages for routine shoot-tip culture. Although freshly extracted explants are recommended, storage of uprooted suckers or trimmed explants for 2â4 days did not significantly affect multiplication rates. The effect of varying levels of 6-benzylamino purine (BAP) was studied in Petite Naine (Dwarf Cavendish), Gingeli and Mamoul clones to determine the optimum level of cytokinin for culture initiation and for subsequent rapid multiplication. To avoid the occurrence of somaclonal variation, modified MS supplemented with BAP at 5mg/L from initiation to 5th subculture and then using BAP at 2mg/L until 9th subculture was optimum for Petite Naine with 800 shoots produced per explant. For Mamoul clones, BAP at 5mg/L was also optimum while for the Gingeli banana BAP at 8 mg/L from initiation to 5th subculture followed by BAP of 2mg/L for further subcultures produced over 800 shoots from explant after 10 subcultures. For rooting, modified MS medium devoid of any plant growth regulator or containing 1mg/L IAA was significantly superior to other auxin sources. Low cost options for weaning and hardening of plantlets was developed. This consisted of placing plantlets in trays containing appropriate low-cost medium and covering them with transparent plastic cover for 1 week in shadehouse, with manual watering. Appropriate low-cost medium for weaning of plants developed was flyash and scum mixtures (with at least 50% flyash) or sterile soil and manure (1:1) mix, which produced significantly superior plantlets at a faster rate than any other medium. For successful weaning and to avoid transplantation shocks plantlets should be at least 1.5cm tall (although 2.5 cm tall are best) with medium filled in the tray to at least 4cm depth. The regenerated plants are currently being field evaluated and preliminary observations indicate normal plant development.
Keywords
Banana,Agriculture,Biotechnology,Ollier and Dwarf Cavendish