Host species specificity of the goldenrod rust fungus and the existence of rust resistance within some goldenrod species

Five out of six species of goldenrod at a study site in Ontario had rust pustules in the field and also developed pustules after laboratory inoculation with urediospores of a single-pustule isolate of the rust fungus (Coleosporium asterum) obtained from Solidago canadensis. This isolate also successfully infected seedlings of S. canadensis and an additional goldenrod species from British Columbia. Light microscopy revealed low levels of spore germination and high levels of failed infection attempts even on susceptible plants; in S. canadensis, infection commonly failed before the formation of the first haustorium, a phenomenon typical of nonhost resistance and indicative of a degree of nonspecific incompatibility between fungus and host. Only 2 out of over 200 S. canadensis seedlings from Ontario or British Columbia lacked pustules after repeated inoculations compared with 7 out of 36 for Solidago rugosa seedlings from the study site. Microscopically, infection sites in most of these resistant plants resembled those in crop plants with parasite-specific, single-gene resistance. The data raise the possibility that the fungus has exerted a stronger selective pressure for parasite-specific resistance on S. rugosa than on S. canadensis. Key words: Coleosporium asterum, goldenrod, rust fungi, Solidago, specificity.

Control of Rust of China Aster and Comments on the Name of the Pathogen

Rust, Coleosporium asterum, of China aster, Callistephus chinensis, is a serious problem on plants grown for cut flowers in California. Control of the rust resulted from 3 applications of fungicides at 3-week intervals. Funginex® (triforine) gave the best control. Bayleton® (triadimefon) and Fore® (mancozeb) gave good control. Plantvax® (oxycarboxin) and Physan® (a quanternary ammonium chloride compound) failed to control the fungus satisfactorily. The use of the binomial Coleosporium asterum, formerly called C. solidaginis, is questioned.

Studies of western tree rusts. VIII. Inoculation experiments with conifer needle rusts (Melampsoraceae)

Results from 22 cross-inoculation experiments provide confirmatory and new information on broom rusts of spruce and fir (Chrysomyxa arctostaphyli Diet. and Melampsorella caryophyllacearum Schroet.) and needle rusts of pine, larch, and fir (Coleosporium asterum (Diet.) Syd., Melampsora paradoxa Diet. & Holw., Pucciniastrum epilobii Otth, Uredinopsis longimucronata Faull, U. phegopteridis Arth., and U. struthiopteridis Stoerm. ex Diet.). New host and distribution records are confirmed by inoculation. Cone rust of alpine fir is shown to be caused by Pucciniastrum epilobii. The need for further study of needle rust of pine (Coleosporium) and a monographic treatment of the willow rusts (Melampsora epitea complex) is suggested.