Assessment of the rooting abilities of four African mahogany species using leafy stem cuttings

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Efforts to restore degraded forest lands using indigenous and important timber species including those of the Meliaceae family exist. Success of this exercise will, however, be dependent on the availability of quality planting material as African mahoganies are attacked by the shoot borer moth, Hypsipyla robusta. Existence of genotypes tolerant to the shootborer, therefore necessitates propagation using vegetative propagation in raising seedlings. This study was to develop vegetative propagation techniques using leafy stem cuttings and simple non-mist propagators to assess the effects of African mahogany species (Khaya grandifoliola, Khaya ivorensis, Entandrophragma angolense, and Entandrophragma utile). It also assessed rooting-media (river-sand, top soil and a mixture of the two (50:50 v/v) and age of stock-plant (1, 4, 7 and 12 years) of K. grandifoliola on the rooting ability. Anatomical properties of the shoots were studied through tissue (vessel, fibre and parenchyma) counts from transverse sections and measurements of vessel and fibre dimensions from macerated samples to determine the variability between species and ages and their relationship to the rooting ability of the stem cuttings. Rooting ability ranked as follows among the species: K. grandifoliola (73%) > K. ivorensis > E. angolense > E.utile (30%). Rooting percentage was highest for cuttings placed in the mixed medium for the Khaya species. This was 73% in K. grandifoliola and 65% in K. ivorensis. The Entandrophragma species recorded their highest rooting in top soil 46% in E. angolense and 40% in E. utile and lowest for both in river-sand: 37 % and 30 % respectively. Age of stock-plant influenced rooting ability in stem cuttings of K. grandifoliola: 77% (age 1) > 70% (age 4) > 68% (age 7) > 60% (age 12). Stem cuttings taken from the middle portions of shoots recorded the highest rooting ability in all the four species (73% (K. grandifoliola), 65% (K. ivorensis), 54% (E. angolense) and 45% (E. utile) and also in 4 years (70%), 7 years (60%) and 12 years for (55%) K. grandifoliola stem cuttings. Sections from the four species showed similarities in vessel, parenchyma and fibre proportions with parenchyma ranking as follows: K. grandifoliola (35.96%) > E. utile (39.92%) > K. ivorensis (34.92%) > E. angolense (34.25%) and fibre ranking as follows: E. angolense (38.79%) > K. ivorensis (38.33%) > E. utile (37.83%) > K. grandifoliola (37.75%). Fibre and vessel proportions increased with increasing age of stock-plant from age 1year to12 years, while parenchyma proportion decreased with increasing age of stock-plant of K. grandifoliola. The high proportion of parenchyma (39.96%) corresponded with high rooting ability (73%) in K. grandifoliola, while high proportion of fibre (38.79%) in E. angolense corresponded with low rooting ability (30%). Fibre diameter, fibre lumen diameter and double fibre wall thickness ranked as follows in the species: E. utile > E. angolense > K. grandifoliola > K. ivorensis. Aside the vessel diameter, fibre and vessel dimensions ranked as follows in the four different aged stock-plants of K. grandifoliola: 1 < 4 < 7 < 12. The study strongly supports the idea that the four African mahogany species can be propagated vegetatively using stem cuttings which are important for ex-situ conservation and restoration of the mahogany species in Ghana’s forest estate, especially older trees (4, 7 and 12 years) that have shown tolerance to the mahogany shootborer.
A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the Degree of Master of Philosophy, July-2011