. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. RELATION OF SIZE OF BALD SPOT AND FREQUENCY OF VISIBILITY IN SIM PHOTOS 3F SPORES. s--z~ . z: - A I (A = atertensrs J I ^ A | -_ 8 fO= abietis-conoxtensis J s ;:- o I J ( ocddentafs ) _ ~ _ ~ ~_ r' " _ ~ abietis-canadensis, tw o were found in 1981 in Wis- consin, and five were found in 1982, three from Wisconsin and one each from Michigan and North Dakota, Melampsora abiens-canadensis was not found in Minnesota collecti
. Recent research on foliage diseases : conference proceedings : Carlisle, Pennsylvania, May 29-June 2, 1989. Leaves Diseases and pests United States Congresses. RELATION OF SIZE OF BALD SPOT AND FREQUENCY OF VISIBILITY IN SIM PHOTOS 3F SPORES. s--z~ . z: - A I (A = atertensrs J I ^ A | -_ 8 fO= abietis-conoxtensis J s ;:- o I J ( ocddentafs ) _ ~ _ ~ ~_ r' " _ ~ abietis-canadensis, tw o were found in 1981 in Wis- consin, and five were found in 1982, three from Wisconsin and one each from Michigan and North Dakota, Melampsora abiens-canadensis was not found in Minnesota collections (57) in either year. Neither species was found in collections (12) from Iowa. Of collections of M. abietis-canadensis, three were on native Populus spp., once each from bigtooth aspen (P. grandidentata), balsam poplar (P. balsamifera), and trembling aspen (P. tremuloides) and once from an exotic species, P. tremula L. all in Wisconsin. Both M. albertensis and M. abietis-canadensis were collected from hybrid poplar clones. Two leaves examined contained pustules of both M. medusae and M. albertensis and two others had both .V/. medusae abietis-canadensis. All four mixed infections were from hybrid poplars. Discussion Our finding of mixed infections on single leaves in several instances suggests that mass field collections of spores for controlled inoculations may well contain mixtures, even if such collections are restricted to single plants or clones. Mixed infection on hybrid poplars has been reported previously (14). Ziller (37,38) extentensively studied both the aecial and telial host ranges of Melampsora and concluded (39) albertensis should by synonymous with M. medusae. We believe, based on present work, that M. albertensis can be distinguished from M. medusae with resonable certainty from uredospore collections. Admittedly the numbers of M. albertensis included here are low, and more extensive collections might reveal a continuum of bald spot sizes. T
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