EXOTIC, EMERGING, RE-EMERGING, AND INVASIVE PLANT DISEASES OF HORTICULTURAL CROPS
Location: Horticultural Crops Research
Title: Invaded range of the blackberry pathogen Phragmidium violaceum in the Pacific Northwest of the USA and the search for its provenance
Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2013
Publication Date: February 21, 2013
Citation: Morin, L., Gomez, D., Evans, K., Neill, T.M., Mahaffee, W.F., Linde, C. 2013. Invaded range of the blackberry pathogen Phragmidium violaceum in the Pacific Northwest of the USA and the search for its provenance. Biological Invasions. DOI 10.1007/s10530-013-0413-3.
Interpretive Summary: In 2005, blackberry rust was found on feral blackberries near Bandon, Oregon. Subsequent surveys found servere rust infections in commercial evergreen blackberries and feral blackberries in western Oregon. Significant yield losses were associated with blackberry rust in several commercial evergreen blackberry fields. An extensive survey of feral and native blackberries throughout Oregon, Washingtion, and California was conducted in 2006 to discern the extent of the blackberry rust invasion. A population genetic study to explore the origins of the U.S. introduction of Phragmidium violaceum (blackberry rust). A collection of U.S. isolates were compared to isolates from Europe and Australia based on 11 microsatellite loci. The disease was found west of the Cascades and Sierra Mountains from Santa Cruz, CA to the Canadian Boarder below 1500ft. Analyses of the microsatellite data indicated that the U.S. population did not originate from Australia. It appears that the U.S. population is not a direct descendent of the European population (presumed center of origin). Thus it is likely that Blackberry was present in the United States for a long period of time prior to its discovery or the introduction occurred from another population (e.g. Chile).
Field surveys in 2006 confirmed the rust fungus Phragmidium violaceum was widespread on Rubus armeniacus and R. laciniatus in the Pacific Northwest of the United States. The origin, evidence of a founder effect and dispersal pattern of this obligate biotrophic pathogen in the United States were investigated by comparing the genetic diversity and structure of isolates from the United States, Europe (the native range) and Australia, where an invasion occurred in 1984. Analysis of 11 microsatellite loci revealed 74 unique genotypes, with the European population having a significantly higher level of allelic diversity and number of private alleles compared to the other populations. Principal coordinate analysis (PCA), Analysis of Molecular Variance and pairwise comparisons of F confirmed a strong level of differentiation among continental populations, with little divergence between isolates from the USA and Europe, but a high level of differentiation between these isolates and those from Australia. These results were broadly supported by the Bayesian cluster analysis, which indicated that at K = 3 the clustering of the isolates corresponds to their geographic origin. Bayesian clustering, PCA as well as low migration rates from Europe to the USA suggest that the USA population is not a direct descendant from the European population. There was a weak association between genetic and geographic distance among the USA isolates, suggesting invasion was initially localized prior to dispersal or that the population may have been present for some time prior to first detection. The possible pathway of introduction of P. violaceum into the USA is discussed.