POPULATION-STRUCTURE AND MYCELIAL PHENOTYPIC VARIABILITY OF THE ECTOMYCORRHIZAL BASIDIOMYCETE LACCARIA BICOLOR (MAIRE) ORTON

Mating type allele distribution and phenotypic variability were invest igated in field populations of Laccaria bicolor. Sporophores associate d with Norway spruce (Picea abies), colonized by natural sources of in oculum and growing in a seed orchard, were sampled to obtain dikaryoti c strains and assay their phenotypic variability for traits important to the symbiosis. Basidiospores were also collected for mating type an alysis of different mycelia. Four sporophore mating types were identif ied containing seven A and five B factors. Outbreeding efficiency was estimated at 73.8% and the population was slightly inbred. Crosses wit h previously characterized L. bicolor strains from two nearby populati ons identified in total six sporophore mating types and ten A and nine B factors, for an estimated outbreeding efficiency (85.7%) similar to previous studies of more spatially disparate Laccaria spp. population s. Dikaryotic strains were rested for mycelial growth rate, as a measu re of their competitive ability, on agar media containing a soluble (N aH2PO4), or an insoluble (CaH-PO4) phosphate source. Their ability to solubilize the latter was also tested to assess their relative capacit y to access insoluble, inorganic phosphate. In most cases, significant variation was detected among strains from the same site for all varia bles. On three sites (VC4, VC5 and VC7), each determined previously to possess a uniform mycelial genotype, phenotypic variability was likel y due to epigenetic variation among different strains of the same geno type. Possible evidence for di karyon-monokaryon crosses was observed in vivo on one sample site (VC2) where adjacent mycelia shared two mat ing factors. The phenotypic variability of different mycelial genotype s reflected their genetic variability observed as mating type allele d iversity and underlined the importance of basidiospore dispersal in in troducing new genotypes into the population. The reproductive strategi es of L. bicolor are discussed and compared to those of other basidiom ycete species.