Pattern of root initiation by an ectomycorrhizal fungus on hypocotyl cuttings of Larix laricina

Abstract

The rooting pattern of tamarack hypocotyl cuttings produced under the influence of the ectomycorrhizal fungus Laccaria bicolor (Maire) Orton was assessed and compared with the rooting patterns induced by three plant growth regulators. No callus was produced in fungal and control treatments, and the rooting percentages were 93 and 100%, respectively. The fungal treatment caused an upward distribution of roots along the hypocotyls, while in the controls the roots formed only at the base of the hypocotyls. Appreciable callus tissue formation was promoted by all naphtaleneacetic acid concentrations (1, 10, and 50 μM) and rooting percentages never exceeded 10%. A slight swelling at the base of the cuttings was induced by 1 μM indolebutyric acid, whereas higher concentrations (10 and 50 μM) promoted callus tissue formation. Hypocotyls cultured along with the fungus in the auxin-supplemented media did not exhibit any callus tissue formation, and numerous root primordia were initiated on the hypocotyl axis. Callus tissue was absent or negligible on the cuttings treated with ethephon (2-chloroethylphosphonic acid), an ethylene-releasing compound, at 50, 75, and 100 μM. The rooting percentages were optimal at the higher ethephon concentrations, while at 50 μM 93% of the hypocotyls formed roots and root primordia. A redistribution of roots along the hypocotyl was observed with 75 and 100 μM ethephon in a manner similar to the fungal treatment.