Department of Plant Pathology, Cornell University, Ithaca, NY 14853
Department of Horticulture, Iowa State University, Ames 50011
Department of Plant Pathology, Cornell University
Department of Horticulture, Iowa State University
Department of Plant Pathology, Iowa State University
Department of Floriculture and Ornamental Horticulture, Cornell University
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Accepted for publication 8 March 2000.
Five cultivars of Fraxinus americana (white ash) and five of F. pennsylvanica (green ash) were graft-inoculated with three strains of ash yellows phytoplasmas at Ames, IA, and with thrsee other strains at Ithaca, NY. A sixth green ash cultivar was tested only in New York. Trees were allowed to grow in field plots for 3 years. Infection was detected via the DAPI (4′, 6-diamidino-2-phenylindole 2HCl) fluorescence test. Incidence of witches'-brooms on infected trees was greater on white ash than green ash and varied significantly among phytoplasma strain treatments at both locations. Volume growth of infected ash, averaged across cultivars over 2 years in Iowa and 3 years in New York, was 49 and 59%, respectively, as great as that of noninfected trees. Foliar greenness was reduced significantly by infection at both locations, and this reduction was positively correlated with growth reduction. Cultivars at each location varied significantly in growth of noninfected trees and in growth of diseased trees relative to that of nonin-fected trees (a measure of phytoplasma tolerance), but cultivar means for these variables in Iowa were not significantly correlated with those in New York. Green ash cvs. Bergeson, Dakota Centennial, and Patmore and white ash cv. Autumn Applause were above average in tolerance at both locations. Phytoplasma strains at each location varied significantly in aggressiveness as indicated by host growth suppression.
© 2000 The American Phytopathological Society