Incompatibility groups among North American populations of Laetiporus sulphureus sensu lato

Mycelial interactions and allozyme analysis for glucose-6-phosphate isomerase activity were used to evaluate compatibility of pairings of single spore isolates (SSIs) within and between Laetiporus restriction groups (LRGs). SSIs from six collections of LRG II were completely compatible. SSIs from four LRG III collections from western North America were completely compatible, but those from a fifth collection of LRG III, from Michigan, were only partially compatible with those from the western LRG III collections. LRG II SSTs were incompatible with LRG III SSIs, and SSIs of these LRGs were incompatible with SSIs of L. sulphureus, L. cincinnatus, and LRG VI. SSIs from the lone collection of LRG VI were compatible with those of L. sulphureus, which also contains LRGs I and VII. Thus, L. sulphureus s. l. is composed of four Laetiporus incompatibility groups (LIGs): L. sulphureus s. s., L. cincinnatus, LIG II, and LIG III. The LIGs differ in host, pore layer color, geographical distribution, and LRG. Pairings of tester SSIs from each of the LIGs with SSIs from an additional 42 collections of Laetiporus confirm the mutual exclusiveness of the LIGs and the association of the LIGs with the LRGs as well as other characteristics. Therefore, these four LIGs are worthy of recognition at the species level.