Author
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Caesar, Anthony |
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Lartey, Robert |
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Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 9/3/2008 Publication Date: 12/1/2008 Citation: Caesar, A.J., Lartey, R.T. 2008. First report of crown gall caused by Agrobacterium tumefaciens on Euphorbia esula/virgata in Europe. Plant Disease 92(12):1710-1710. Interpretive Summary: In an overseas survey for root diseases of the deep-rooted, aggressive perennial invasive species leafy spurge, crown gall was found on roots and crowns of the weed in 1992 at three locations in eastern Hungary. In subsequent follow-ups to reisolate the bacterium which causes the tumors, despite loss of two sites due to road construction and changes in land management, it was recovered from one of the sites in 2005. Pieces of the galled leafy spurge root and crown tissue were placed in water overnight and aliquots of water containing the bacterial cells which emerged were plated on agar media selective for the crown gall bacterium. Pure cultures from single colonies taken from the isolation plates were tested on sunflower, tomato and kalanchoe. Three isolates forming the largest galls were tested on leafy spurge and each caused galls. The results of a set of biochemical tests designed to differentiate among three major crown gall-causing species of Agrobacterium spp. indicated that these three isolates were Agrobacterium tumefaciens. This bacterium is a member of a complex of soilborne and systemic diseases of European populations of leafy spurge typically associated with stands of this species with lower densities. It also may be an indicator of the intensity of negative feedback in which would help predict the success of biological control when insects are released for biological control. Technical Abstract: Hypertrophy and hyperplasia resembling crown galls were found on roots of Euphorbia esula virgata occurring at a single site (47°34’32.52”N, 21° 27’ 38.31”E) in east-central Hungary in 2005. Leafy spurge (E. esula/virgata) is an invasive species causing substantial economic losses to the value of grazing lands in the northern great plains of the U. S. Thus, it is the target of biological control. In surveys in Europe and China for soilborne diseases of E. esula/virgata between 1992 and 2007, crown gall was not found anywhere else. Large galls resembling crown gall were first noted in 1992 on roots of the weed collected for phylogenetic studies from three locations in east-central Hungary. One of these sites was able to be located again in 2005 and galls collected. Bacteria isolated from the galls using PDA and three media selective for Agrobacterium spp. were picked from plates and subsequently purified on PDA. Sunflower, tomato and kalanchoe plants were inoculated. Three isolates, which formed the largest galls on sunflower, were used to inoculate leafy spurge plants growing in a 1:1:1 peat, sand, Bozeman silt loam potting mix in. The plants were inoculated by puncturing leafy spurge roots just below the soil line with a sterile dissecting needle holding a drop of fluid matrix containing bacterial cells. The tests were repeated. Galls were visible on inoculated plants within 6 weeks. Biochemical tests done prior to and after re-isolation indicated that the causal agent was Agrobacterium tumefaciens. The three isolates of A. tumefaciens from E. esula had identical sequences and clustered most closely with isolates of A. tumefaciens from Tibet and Japan, based on BLAST. Crown gall of leafy spurge has also been found in Montana and western North Dakota, and isolates were identified as A. tumefaciens biovars 1 and 2 (1) (the latter is now known as A. rhizogenes). This the first report of crown gall on Euphorbia esula/virgata in Europe. |
