Abstract
Somaclonal variation induced in vitro during tissue culture can be a problem in clonal micropropagation of elite plants. This study investigated the extent of morphological and genetic similarity or dissimilarity between Melia volkensii in vitro plants (somatic seedlings) obtained via somatic embryogenesis and normal seedlings. Comparisons were made between in vitro plants regenerated directly from cotyledon explants, indirectly from zygotic embryos and normal seedlings of the same parent trees. Regeneration was achieved using half MS medium supplemented with 0.05 mg/l thidiazuron. Shoots were elongated in half MS with 0.1 mg/l BAP plus 0.01 mg/l IAA then rooted in half MS with 0.1 mg/l IBA and 0.1 mg/l NAA. Six morphometric and five meristic characters were used for the morphological characterization. PCR-RAPD markers were used for assessment of genetic similarity or distance. Multivariate analysis using principal coordinates, cluster analysis, analysis of similarities (Anosim) and similarity percentages analysis (SIMPER) revealed significant dissimilarities (p< 0.0001) in morphometric and meristic characters between the in vitro plants and normal seedlings. However, significant similarity (p<0.01) was observed in the RAPD-genic characters of the in vitro plants and normal seedlings. Out of six morphometric traits, taproot length, internode length and shoot height were the most important sources of dissimilarity, cumulatively accounting for 72.37% of overall morphometric dissimilarity. Number of lateral roots was the single most important source of meristic dissimilarity, with 77.02% contribution. Plants regenerated directly from cotyledons were more similar to the normal seedlings in morphological and RAPD-marker characters than those regenerated indirectly from zygotic embryos. This study paves the way for identification of trait-specific RAPD markers for further characterization through sequence-characterized amplified regions (SCARs). Key words : Morphometric, meristic, PCR-RAPD, Melia volkensii, tissue culture, somaclonal variation.
Highlights
Melia volkensii Gürke (Meliaceae) is a drought-tolerant, fast-growing, hardwood multipurpose tree species endemic to the arid and semi-arid lands of Ethiopia, Kenya, Somalia and Tanzania (Orwa et al, 2009)
Seeds used as sources of explants for regeneration of in vitro plants and for germination into normal seedlings were obtained from the same cluster of five M. volkensii trees growing on a farm situated in Mavuria provenance in Mbeere, Embu county, eastern
Significant morphological variation was observed between the regenerants and wild seedlings in morphometric and meristic traits
Summary
Melia volkensii Gürke (Meliaceae) is a drought-tolerant, fast-growing, hardwood multipurpose tree species endemic to the arid and semi-arid lands of Ethiopia, Kenya, Somalia and Tanzania (Orwa et al, 2009). M. volkensii outperforms other tree species found in arid and semi arid parts of Kenya, and has a higher profitability than Eucalyptus camaldulensis and Grevillea robusta in these environments (Wekesa et al, 2012). Volkensii outperforms other tree species found in arid and semi arid parts of Kenya, and has a higher profitability than Eucalyptus camaldulensis and Grevillea robusta in these environments (Wekesa et al, 2012) It has vast potential for arid afforestation and commercial tree farming in the region but this is hampered by difficulties in propagation via seed and vegetative means. Tissue culture processes often induce somaclonal variations which can be problematic and require detailed characterization before the technique can be adopted for mass propagation of any plant species
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