Partial characterisation of the fruiting inducing factor from the polypore Phellinus contiguus

Filtrates from cultures of wild isolates of Phellinus contiguus grown on liquid medium containing malt extract induced precocious fruiting of this resupinate polypore when tested in a bioassay. Active filtrates were analysed using gel filtration, HPLC and GC-MS and were compared with filtrates from single spore progeny, two of which lacked fruiting inducing activity. The active material was polar and heat stable, passed through both anion and cation exchange columns and had a mol. wt less than approx. 1000. Fractionation using HPLC on amino-silica yielded one fraction which was active on its own and a second, later eluting fraction, which had scarcely detectable activity when alone, but when combined with the first fraction had much higher activity than either alone. GC-MS showed that both this first fraction and the most active fraction from P2 gel filtration were rich in mono- and disaccharide sugars. In comparison with fractions from parallel inactive filtrates, all active fractions contained more myo -inositol and a relatively high glucose/disaccharide ratio. It is suggested that a combination of high concentrations of myo -inositol and apoplastic glucose may be required for initiation of fruiting in P. contiguus. Although additional work is needed, this view is consistent with known features of growth and fruiting in white rot fungi.