ISOZYME DIVERSITY AMONG HARD PINE STEM RUST FUNGI IN THE WESTERN UNITED-STATES

Isozyme analysis was used to determine species relationships and diver sity among stem rust fungi (Cronartium and Peridermium spp.) infecting hard pines (subg. Pinus) in the western United States. Electrophoresi s was carried out on aeciospore extracts of 270 hard pine stem rust is olates representing nine species and forms. Consistent banding pattern s (electromorphs interpreted as phenotypes) were obtained for all isol ates at 11 enzyme loci. Within species groups, multilocus phenotypes w ere diverse at several loci. Nevertheless, each species exhibited a un ique set of phenotypes that distinguished it from all others. For diag nostic purposes, banding patterns from just two loci were sufficient t o distinguish all species and most forms or races examined. Two taxa t hat were thought to be forms of existing species may be new, undescrib ed species. For comparison with western hard pine stem rusts, multiloc us phenotypes were determined for 13 additional isolates of four relat ed pine stem rust species. Phenotypes for all rust species were analyz ed in all possible combinations using pairwise distance analysis (neig hbor-joining). When Cronartium ribicola is treated as the outgroup, th e resulting phenogram groups all 72 multilocus phenotypes into distinc t species clades. Origins of autoecious, short-cycled Peridermium spp. may be inferred from their placements relative to macrocyclic, hetero ecious Cronartium spp.