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Highlights: [•] Globally, the importance of bananas for food security is well known and documented. [•] Use of the micropropagation technique helps to meet increasing demand for bananas. [•] High rate of somaclonal variants remain a major bottleneck during micropropagation. [•] The role of BA and topolins on genetic fidelity was compared at same concentration. [•] Some topolins could reduce genetic variability among micropropagated plantlets. [ABSTRACT FROM AUTHOR]

Abstract: The effect of five topolins (meta-Topolin= mT; meta-Topolin riboside= mTR; meta-Methoxy topolin=MemT; meta-Methoxy topolin riboside=MemTR and 6-(meta-methoxy)-9-(tetrahydropyran-2-yl)-topolin=MemTTHP) on the photosynthetic pigments and leaf structures of micropropagated ‘Williams’ bananas was compared with the commonly used benzyladenine (BA). Surface-decontaminated explants were cultured for 70 d on modified Murashige and Skoog (MS) basal medium and supplemented with 10, 20 or 30μM cytokinins (CKs). At 10 d intervals, the photosynthetic pigments were quantified via spectrophotometric methods for 7 cycles. Generally, the maximum pigment content was attained between 40 and 50 d. The control plantlets had the highest pigment content (1150μg/g FW). Among the CKs, 10μM MemTTHP generally had the best pigment stimulatory effect at the same period. After 40 d, scanning electron microscopy (SEM) of the foliar surface showed that the stomata density was highest in 10μM MemTTHP-treated and lowest in 10μM MemTR-treated plantlets. The stomatal structure and pore area also varied with the type and concentration of CK added. Generally, prolonging culture duration as well as increasing CK concentrations reduced the pigment content. However, the drastic breakdown in chlorophyll pigments beyond 50 d was slightly inhibited by the presence of mT, mTR, MemTTHP and BA compared to the control. The CK-treated plantlets at equimolar concentration had comparable chlorophyll a/b and total chlorophyll/carotenoid ratios after 10 d; probably as an adaptive measure. At the end of the current study, 10μM mT and mTR plantlets remained green as reflected by the higher total chlorophyll/carotenoid ratio as well as by the visual observations. A well-developed photosynthetic apparatus enhances the survival of in vitro plantlets during the acclimatization stage. Current findings provide some insight into the role of meta-topolins on photosynthetic parameters in vitro, which inevitably partly contributed to the better acclimatization capability of meta-topolin-regenerants. [Copyright &y& Elsevier]

Abstract: The effect of the type and concentration of plant growth regulators and sub-culturing on somaclonal variation were studied in Cavendish banana cv. ‘Zelig’ obtained from African Biotechnologies Ltd., South Africa. In vitro grown plants at the fourth multiplication cycle were used for the investigation. Auxins (IAA, IBA and NAA) and cytokinins (BA and TDZ) were used to multiply shoots for 10 generations. Bands generated through RAPD-PCR were scored according to whether they were present (1) or absent (0) to determine the extent of somaclonal variation. Results were then analyzed using cluster analysis. The relationship between multiplication rate and somaclonal variation was assessed using correlation analysis. Results indicated that treatments with higher multiplication rates produced more variants; sometimes as high as 72%. Dwarf off-types accounted for 88% of the variation. A dwarf-specific band, about 1500kb in size, was amplified by the primer OPC-15. The band appeared consistently in normal plants but was absent in all dwarf plants. [Copyright &y& Elsevier]

Highlights: [•] A total of 47 endogenous cytokinin-forms grouped into 9 classes were quantified. [•] Tissue-cultured plants had more endogenous cytokinin levels than acclimatized plants. [•] 9-Glucosides were the major metabolites in tissue-cultured and acclimatized plants. [Copyright &y& Elsevier]