The significance of mycorrhiza in regeneration of merbau [Intsia bijuga (Colebr.) O. Kuntze] originating from Papua

Abstract

Merbau [Intsia bijuga (Colebr.) Kuntze] is considered as one of valuable timber tree in South-East Asia which has long been exploited but its silviculture for supporting plantation development is neglected. How to produce good quality of merbau seedlings by using generative and vegetative regeneration methods collaborated with the application of ectomycorrhizal association on merbau for improving the performance of the seedlings is an important issue to be answer. The research was carried out in a series of laboratory experiments and field work (exploration). Exploration was done in merbau natural stands, plantation and nurseries for collecting merbau seeds, wildlings, soils suspiciously containing ectomycorrhizal propagules, sporocarps and ectomycorrhizal root tips of merbau. While experiments to find out the efficient method of merbau regeneration through vegetative and generative propagation were conducted in the laboratory. Merbau was easily regenerated through seeds and shoot cuttings. Merbau seeds revealed variation in morphology and seed weight. Seed nicking followed with seed soaking in low concentration of sodium hypochlorite (0.525 %) for 15 minutes and then in hot water for 24 hours gave the highest percentage of seed germination of merbau (78.67%). Seed weight of > 2.25 g gave better in mean germination time and height performance of the seedlings. The application of auxin IBA/NAA (1000 ppm/500 ppm) gave highest percentage of rooted cuttings (77.1%) and of rooted and sprouted cuttings (50.0%). Merbau regeneration by micro cuttings in vitro was successful to produce explants although the regeneration was in low frequency. The constraints are mainly related to early defoliation of leaves and shoots, and the cessation of the growth after 2 months in the culture medium. Maintaining relatively high concentration of nitrogen and phosphate content close to those of MS medium likely gave beneficial effects for shoot initiation of micro-cuttings of merbau in vitro. Only one species of ectomycorrhizal fungus was found associated with merbau [Intsia bijuga (Colebr.) Kuntze]. The fungus formed mycorrhizae with monopodial pinnate branching type. The fungus was identified belonging to the genus of Scleroderma. The fungus could be cultured in both agar and semi-solid media of MMN. Other ectomycorrhizal fungi i.e. Scleroderma sinnamariense, Scleroderma columnare, Scleroderma. dictyosporum and Pisolithus sp were not able to form ectomycorrhizae with merbau seedlings. Inoculation using both suspension of spore masses and mycelia aggregates of Scleroderma sp did not gave any influences to the cuttings success. On the other hand the inoculation effectively improved the seedling and the transplanted-rooted cutting performance.