IN-VITRO EFFECT OF LACCARIA-BICOLOR S238-N AND PSEUDOMONAS-FLUORESCENS STRAIN BBC6 ON ROOTING OF DE-ROOTED SHOOT HYPOCOTYLS OF NORWAY SPRUCE

The ectomycorrhizal fungus Laccaria bicolor S238 N and the bacterium P seudomonas fluorescens BBc6 were used separately and in combination to induce in vitro rooting of de-rooted shoot hypocotyls of Norway spruc e (Picea abies (L.) Karst.). When the culture medium was supplemented with tryptophan, a precursor of indole-3-acetic acid (IAA) synthesis, the presence of the ectomycorrhizal fungus increased the percentage of hypocotyls forming roots; furthermore, both the fungal and bacterial inoculations enhanced the number of roots formed per rooted hypocotyl. Similar results were obtained by adding exogenous IAA (5 and 10 mu M) to the rooting medium. After the rooting phase, the fungal inoculatio n enhanced adventitious root elongation and branching as well as the a erial growth of the cuttings. Pseudomonas fluorescens BBc6 had no effe ct on these parameters. The production of IAA by pure cultures of L. b icolor S238 N and P. fluorescens BBc6 was estimated by immunochemical analysis using specific anti-IAA antibodies. Both L. bicolor S238 N an d P. fluorescens BBc6 synthesized IAA in pure culture and synthesis wa s stimulated in the presence of tryptophan. Thus, the effect of the fu ngus in stimulating adventitious root formation and subsequent elongat ion and branching can be attributed, at least partially, to the synthe sis of ZAA by the fungus. The finding that P. fluorescens BBc6 had no effect on root elongation and branching although it produced IAA sugge sts that either IAA was not the only parameter involved in the stimula tion of these processes by L. bicolor S238 N or the bacterium produced other compounds that counteracted the stimulatory effects of IAA on r oot elongation and branching.