1ST REPORT OF THE EURASIAN POPLAR LEAF RUST FUNGUS, MELAMPSORA-LARICI-POPULINA, IN NORTH-AMERICA

Melampsora larici-populina, native to Eurasia, was found in October 1991 in hybrid poplar (Populus trichocarpa X P. deltoides) plantations along the Columbia River near Woodland, Washington, and Scappoose, Oregon. Clavate to broadly ellipsoid urediniospores measured 30-49 X 13-16 mum and were echinulate except for an apical smooth patch. Telia were exclusively epiphyllous. Detached leaf inoculations were used to investigate the telial (poplar) host range of three different monouredinial isolates in the laboratory. Clones known to be susceptible in Europe and Australia to M. larici-populina (i.e., P. nigra var. italica and P. X euramericana cv. I-488) were susceptible in these tests, as were 20 clones of P. trichocarpa, the native black cottonwood of the Pacific Northwest. In general, the pattern of susceptibility among 50 clones representing many poplar taxa, including interspecific hybrid classes, was in accord with what is known of the host range of M. larici-populina in Europe and Australia. Pathogenic variation among the three isolates was not observed.