Heterokaryon formation in Thanatephorus cucumeris anastomosis group 2-2 IV.

Thirty single basidiospore isolates (SBIs) obtained from four field isolates of the basidiomycete fungus Thanatephorus cucumeris AG 2-2 IV were examined for heterokaryon formation. SBIs of three of four field isolates (Rh509, 92155 and R94) did not produce a tuft of mycelium in the hyphal interaction zone between paired isolates on 2% charcoal agar. Field isolates Rh509, 92155 and R94 indicated no death of interacting mycelium with their progenies on glass slide and microscopic examination. AFLP (amplified fragment length polymorphism) phenotypes of parent and their SBIs were identical. Field isolates Rh509, 92155 and R94 and their SBIs were homothallic. SBIs obtained from field isolate SA-1 were grouped into two mating types (SBI-M1 and SBI-M2), and a tuft of mycelium was formed between paired SBIs-M1 and -M2. SBIs of field isolate SA-1 indicated that no death and death of interacting mycelium were randomly observed. AFLP phenotypes among SBIs of isolate SA-1 were not identical and were also different from their parent isolate. AFLP phenotypes of tuft mycelia produced between heterothallic SBI-M1 and -M2 were heterokaryotic. The mating system of field isolate SA-1 and its SBIs was heterothallic. Both SBIs-M1 and -M2 further produced tuft mycelium with homothallic field isolates and their SBIs. AFLP banding patterns suggested that tuft mycelium was heterokaryotic produced from between heterothallic and homothallic isolates. Results from these experiments clarified that both homothallic and heterothallic isolates exist in population of T. cucumeris AG 2-2 IV, and that genetic exchange can occur between homothallic and heterothallic isolates.