Assessment of compatibility among Armillaria cepistipes, A-sinapina, and North American biological species X and XI, using culture morphology and molecular biology

Ten single-spore isolates each of Armillaria sinapina, A. cepistipes, and North American biological species (NABS)X and XI were paired in all combinations. A second set of ten single-spore isolates of each species was likewise paired. Each pairing was duplicated for a total of 3280 pairs. Using the standard morphological criteria (e.g., fluffy, crustose) to assess the pairings, A. sinapina exhibited the following compatibility levels: 68% with itself, 5.5% with A. cepistipes, 3.5% with NABS X, and 5% with NABS XI, respectively. Armillaria cepistipes was rated 53%, 6.5%, and 57% compatible with itself and NABS X and XI, respectively. NABS X was 70% selfcompatible and 4.0% compatible with NABS XI. NABS XI was 55% selfcompatible. The intergenic spacer region of the rDNA of each isolate was amplified using polymerase chain reaction and digested with Alu I. Seven distinct restriction fragment length polymorphic (RFLP) patterns were observed: two in A. cepistipes, two in A. sinapina, one in NABS X, one in NABS XI, and one that was common to NABS XI, and A. cepistipes. By using the RFLP patterns as markers to assess the outcome of the pairings, it was determined that, in general, the morphological ratings were an accurate reflection of nuclear combination. Combining the RFLP and pairing results confirms that NABS XI is compatible with A. cepistipes and should be considered conspecific. A. sinapina, NABS X, and A. cep istipes are compatible to a very limited degree in culture, but not enough evidence exists to warrant reducing any to synonomy. Therefore, we believe NABS X should be formally described as a new species of Armillaria.