VARIATION IN PATHOGENICITY AND VIRULENCE OF ISOLATES OF ARMILLARIA-OSTOYAE ON 8 TREE SPECIES

Thirteen isolates representing 10 genotypes of Armillaria ostoyae, obt ained in northern New Mexico from Pinus ponderosa, Abies concolor, Pse udotsuga menziesii, Pinus strobiformis, Picea pungens, and Populus tre muloides were used to inoculate seedlings of these hosts and Larix occ identalis and Pinus contorta var. latifolia. At 18 months there were n o significant differences (P > 0.05) in mortality among the eight host s, or in virulence across all isolates except for one isolated from P. pungens, which failed to infect any trees. After three growing season s (30 months), significantly more (P < 0.05) P. contorta var. latifoli a were infected than either A. concolor or P. menziesii. Pinus pondero sa, the dominant species in this region, did not differ significantly from either of the exotic species (L. occidentalis and P. contorta var . latifolia) in susceptibility to infection or mortality. Populus trem uloides was significantly (P < 0.05) more tolerant than conifers, bein g frequently infected but rarely killed. A fungal isolate's ability to incite disease was highly correlated with its production of rhizomorp hs (r = 0.94, P < 0.01). Across all fungal isolates and hosts save P. tremuloides, the order of the isolate's ability to incite disease matc hed its order in killing hosts.