A method for determining indole-3-acetic acid (IAA) production in mycorrhiza-forming fungi was developed. Culture medium and the fungal mycelium were, extracted with ethyl ether together with deuterated IAA as an internal standard, and the extracts thereafter evaporated to dryness. The dry extracts were then silylated in pyridine with BSTFA and analysed by gas chromatography-mass spectroscopy. Compared to other methods the procedure required a minimum of preparatory work, gave good reproducibility and a standard deviation of acceptable level for studies involving biological material.
The method was used to study IAA production in 16 mycorrhiza-forming fungi. Results indicated large differences in the ability of the fungal strains to produce IAA. Pisolithus tinctorius 185, a strain previously shown by other workers to give a strong root infection in field experiments, produced the largest amount of IAA. Several other fungi showing high IAA values also infected plant roots with relative ease in laboratory experiments.