Micropropagation of Corymbia hybrid and its interaction with Laccaria laccata under in-vitro condition

Corymbia is credited with high growth rate and multiple uses and is planted to meet the ever increasing demand for timber. The Corymbia hybrid selected for the study, has displayed about two times height, girth and collar diameter as compared to its parents. Micropropagation has been a powerful tool for the multiplication of such hybrids by maintaining their hybrid vigour. To reduce mortality and release the stress upon transplantation as well as to provide fast growth, establishment of ectomycorrhizae on micropropagated plantlets is suggested as these help in nutrients uptake and reduce environmental stresses. Therefore, the present work was undertaken with the objective of studying interaction of Laccaria laccata, an ectomycorrhizal fungus, with micropropagated plantlet of the hybrid under in-vitro conditions. Nodal segments containing axillary buds from newly developed fresh shoots were taken and treated with 1% carbendazim (50% WP) for 10 minutes followed by surface sterilization using 0.1% mercuric chloride for 2 minutes. The explants were incubated in Murashige and Skoog (MS) medium supplemented with 3% sucrose, BAP (2 mg/l) and NAA (1 mg/l) for axillary bud induction and shoot initiation. Shoot multiplication was achieved in the same medium and regular subculturing was carried out on MS with BAP (1 mg/l). After 4-6 subculturing sufficient juvenility was achieved and thereafter half strength MS medium devoid of plant growth regulators was used to get elongated shoots to induce rooting. Best rooting was observed in half strength MS medium supplemented with IBA (0.1 mg/l). Laccaria laccata was multiplied using Modified Melin Norkrans (MMN) medium and inoculated into rooted plantlets in vermiculite having MMN/ MS medium or in soil under in-vitro conditions. Plantlets died within 1 and 2 months of inoculation in vermiculite and soil respectively. This may be attributed to the ready availability of nitrogen and phosphorus in MMN and MS media and more competency