Abstract
The identification of drought tolerant banana varieties under natural environment is complicated by difficulties in field management, variation in phenotype and unexpected rainfall events. A study to develop an alternative and rapid technique to screen for drought tolerant banana varieties by an in vitro technique was carried out. Effects of 0.09 M sucrose, 0.09 M sorbitol and 0.0 M sugar on growth of banana plantlets were comparedunder in vitro conditions. Results from this experiment proved that sorbitol is not a source of energy for in vitro banana plantlets and it could be used as a neutral osmotic inducer. Exploration of different levels of osmotic stress induced by 0.1 to 0.5 M sorbitol in the media and their effects on the growth of banana plantlets proved that the concentration of 0.2 M sorbitol is the highest concentration to reveal different growth parameters. The application of this concentration on banana varieties of Williams, Popoulou, Obino l'Ewai, Lep Chang Kut, Mbwazirume (negative control: drought sensitive), and Cachaco (positive control: drought tolerant) showed that all varieties were affected by sorbitol osmotic stress but the degree of sensitivity is different. Significant differences in reduction of gain of fresh and dry weight, new roots and leaves, and leaf area were observed between Cachaco and Mbwazirume. For most growth parameters, Cachaco showed the lowest reduction and Mbwazirume presented the highest reduction due to osmotic stress. The varieties Williams and Lep Chang Kut showed a level of drought tolerance after Cachaco. Lep Chang Kut had the lowest reduction of gain of new root and fresh weight, and water content; whereas, Williams occupied the second position of low reduction of gain of leaf area, number of leaves, and the third position in low reduction of gain of new root and dry weight. After, Obino l'Ewai occupied the fourth position and Popoulou came as the fifth position. Mbwazirume was the last in the tolerance of sorbitol induced osmotic stress with high reduction in many growth parameters evaluated. From this study, an in vitrotechnique to screen drought tolerant banana varieties was developed, and the drought tolerance of Cachaco and Lep Chang Kut and drought sensitivity of Mbwazirume were proved. The total gain of fresh and dry weight, number of new leaves and leaf area were identified to be appropriate growth parameters for identifying drought tolerant banana varieties under in vitro condition. Key words: Banana, drought tolerance, in vitro screening, osmotic stress, sorbitol.
Highlights
Lep Chang Kut had the lowest reduction of gain of new root and fresh weight, and water content; whereas, Williams occupied the second position of low reduction of gain of leaf area, number of leaves, and the third position in low reduction of gain of new root and dry weight
Three different culture media; regeneration culture medium (RCM), RCM omitted sucrose and RCM where sucrose was replaced by sorbitol were compared to verify if sorbitol could be metabolised by in vitro banana plantlets
The results of this study revealed that the growth parameters related to leaves (NL, LA), gain of fresh weight (GFW) and gain of dry weight (GDW) are relevant for identifying drought tolerant banana varieties under in vitro condition
Summary
Banana is the fifteenth of the world’s imported commodities and the fourth most important food crop after rice, wheat and maize in many developing countries It contributes as a source of food, employment and incomes in its major production areas (Heslop-Harrison and Schwarzacher, 2007; FAOSTAT, 2010). It has been observed that fibres of banana leaves exhibit the highest ash, carbon and cellulose content, hardness and tensile strength (Jústiz-Smith et al, 2008) These fibres serve in various handicraft to fabricate baskets, mats, table mats, photo frames, ear rings, souvenir boxes, bags, wall hangings, trays, hats, hand bags, season cards, folders, key holders, neckties, bow ties, waist coats, necklaces and other useful materials (Handcrafts, 2006). Its production is challenged by biotic and abiotic constraints
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