The role of topolins in micropropagation and somaclonal variation of banana cultivars ‘Williams’ and ‘Grand Naine’ (Musa spp. AAA)

Abstract

The effect of the cytokinins mT (metatopolin), mTR (meta-topolin riboside), MemT (metamethoxy topolin) and MemTR (meta-methoxy topolin riboside) on micropropagation of banana cultivars 'Williams' and 'Grand Naine' was studied and compared to BA (6-benzylaminopurine). In vitro cultures, at the third sub-culture level, were purchased from African Biotechnologies (Pty) Ltd., South Africa. These were then sub-cultured on MS media containing 7.5, 15 and 30 lM of all the cytokinins tested. Results recorded after 6 weeks of growth demonstrated that there were statistically significant differences between the parameters analyzed for the treatments. Superior multiplication rates were recorded for mT and mTR treatments. This result was consistent when compared to BA at 22.2 lM (previously published standard concentration). Contrary to previous findings with other species, these cytokinins inhibited rooting. The effect on somaclonal variation was not significantly different when BA, mT and mTR were tested at the seventh multiplication cycle for 'Williams' banana. These results support the possible use of topolins as an alternative to BA for Cavendish banana tissue culture. The role of these cytokinins on somaclonal variation however, requires a more stringent investigation as the results obtained in this investigation could have been influenced by carry-over effects from the initial cultures.

Epigenetics in plant tissue culture

“…One possible improvement of the procedures is in the choice of cytokinin. In micropropagation usually benzylaminopurine (BAP) is added but another cytokinin, metatopolin, is often just as effective with respect to the breaking of apical dominance (so resulting in a similar propagation factor) but has less negative side-effects (Bogaert et al 2006;Valero-Aracama et al 2009; but see Bairu et al 2008).…”

Study of Genetic and Phenotypic Variability among Somaclones Induced by BAP and TDZ in Micropropagated Shoot Tips of Banana (Musa spp.) Using RAPD Markers

“…Ray et al (2006) reported no morphological variation among the regenerated clones during in vitro micropropagation, acclimatization and transfer to the field conditions. This contrary result could be due to application of optimum concentration of BAP (22.2 µM) in the multiplication medium as previous reports (Kalimuthu et al, 2007;Venkatachalam et al, 2007;Bairu et al, 2008;and Shirani et al, 2009) and indicated that 22.2 µM of BAP is the optimum cytokinin concentration for micropropagation of most banana cultivars. The main side effect of TDZ during micropropagation process is creation of morphological changes such as abnormal shoots (Huetteman and Preece, 1993).…”

“…Ray et al (2006) showed that percentage of polymorphism by RAPD were 1.75 and 0.83 in 'Robusta' and 'Giant Governor', respectively. This significant reduction in percentage of polymorphism reported by these authors could be due to the only one concentration of BAP applied in the medium in a way that this concentration has been previously approved as optimum BAP concentration for banana micropropagation (Kalimuthu et al, 2007;Venkatachalam et al, 2007;Bairu et al, 2008;and Shirani et al, 2009) The effect of BAP on genetic variation has been previously reported for other cultivars of banana (Bairu et al, 2006;Martin et al, 2006;Ray et al, 2006;EL-Dougdoug et al, 2007;Mohamed, 2007;and Sheidai et al, 2008). Bairu et al (2006) studied the correlation between multiplication rate and somaclonal variation, their results showed that treatments with high multiplication rate caused more variation.…”

“…El-Dougdoug et al (2007) recorded 25% polymorphism among in vitro micropropagated banana which was closer to the findings reported in this study. Bairu et al (2008) reported that BAP at 22.2 µM did not have any effect on somaclonal variation and they attributed the observed somaclonal variations to factors such as number of subculture. However, a broad range of BAP concentrations (0 µM to 44.4 µM) applied in the present study showed the existence of polymorphism among regenerated somaclones.…”

“…Regarding that genomic DNA tested in this study was extracted from the leaves of the three parental genotypes and their regenerated clones of the 6 th subculture, some parts of polymorphism recorded among the somaclones could be due to increase of the time -period of subculture, as somaclonal variation was reported to be number of subculture dependent (EL-Dougdoug et al, 2007;Bairu et al, 2008;Sheidai et al, 2008).…”