Lilac witches'-broom (LWB), caused by the ash yellows (AshY) phytoplasma, was identified in common lilac (Syringa vulgaris L.) in Cass and Ransom counties in southeast North Dakota in 1997 and 1998. The infected plants were immature, naturally regenerating lilac in the understory of three 57- and 58-year-old Prairie States Forestry Project windbreaks that have lilac as a planted component. In late summer and early fall of 1997, the terminal ends of hardened-off, current-season shoots on more than 100 immature plants were dead, and two to three succulent, late-season shoots were present just below the dead tips. Succulent shoots collected from one such plant in each of two of the windbreaks (both in Ransom Co.) were positive for the AshY phytoplasma, using immunofluorescence (IF) with an AshY phytoplasma-specific monoclonal antibody (1). One of those shoots was also positive with a universal phytoplasma-specific primer pair (R16F2/R2) (2) in a polymerase chain reaction (PCR). Succulent shoots from a plant in the third windbreak (in Cass Co.) were IF negative. In late spring of 1998, more than 100 young plants in two of the same windbreaks (one each in Cass and Ransom counties) had abnormal shoot growth, including combinations of yellow, distorted leaves, multiple shoots, and twig dieback. A shoot from one of two plants sampled in the Ransom Co. windbreak was IF positive. Roots from two of four plants sampled in the Cass Co. windbreak were IF positive, while the other root samples and shoot samples from the same four plants were IF negative. A shoot from one of the IF positive plants was positive for phytoplasmas in a PCR. Witches'-brooms were not observed in the planted lilacs. This is the first report of LWB in North Dakota and in the Great Plains region of North America. While the AshY phytoplasma is known in green ash (Fraxinus pennsylvanica Marsh.) in the Great Plains, this report documents substantial extension of the known range of LWB westward from Wisconsin (3). Lilac is a very important shrub in both rural and urban plantings in the northern Great Plains and is the most commonly planted shrub in North Dakota. With this report, LWB should be considered among the possible damaging agents in lilac in this region.
References: (1) Y. H. Guo and T. A. Chen. Phytopathology 83:243, 1993. (2) I.-M. Lee et al. Phytopathology 83:834, 1993. (3) W. A. Sinclair et al. Plant Dis. 80:468, 1996.