MEIOTIC SEGREGATION AND RECOMBINATION OF THE INTERGENIC SPACER OF THERIBOSOMAL DNA IN THE ECTOMYCORRHIZAL BASIDIOMYCETE LACCARIA BICOLOR

The aim of this study was to clarify the inheritance of the nuclear ri bosomal DNA (rDNA) in the ectomycorrhizal basidiomycete Laccaria bicol or S238N in order to resolve inter- and within-strain relationships in forest ecosystems. PCR amplification of the intergenic spacer (IGS) w as carried out in the dikaryotic mycelium and its haploid progeny. In the dikaryotic mycelium, multiple amplification products were produced for the 25s/5s (IGS1) and 5s/17s (IGS2) intergenic spacers. The 4.5- and 4.0-kb fragments of IGS2 (haplotypes alpha and beta, respectively) were observed to occur in a 1:1 ratio within the haploid progeny as a result of divergent IGS haplotypes in the two separate nuclei. Recomb inant monokaryons having both types of IGS2 occurred at a low frequenc y (6.5%; 60 kb per centimorgan) during meiosis. Haplotypes alpha and b eta of IGS1 cross-hybridized forming heteroduplexes during the PCR tem perature cycle. The two IGS1 haplotypes differed only by the repeat nu mber of a TA(2)C(3) motif and co-segregated with the IGS2 haplotypes. Heteroduplex formation and IGS polymorphism provide information that i s helpful in distinguishing between introduced exotic L. bicolor S238N and indigenous populations of Laccaria spp. in forest ecosystems.