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Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 7/19/2007 Publication Date: 11/1/2007 Citation: Shishkoff, N. 2007. Susceptibility of some lilac cultivars and other members of the Oleaceae to Phytophthora ramorum. Plant Health Progress. 10.1094/PHP-2007-1101-2-RS Interpretive Summary: Phytophthora ramorum causes symptoms on a variety of plant hosts. It was first observed on European nursery stock and in California forests in the mid-1990s; it has now been reported from many countries in the European Union, and has spread in natural areas of California and Oregon. Data indicate that a possible means of spread outside the infected regions in the US has been through infected nursery stock. Since January 2005, the "Emergency Federal Order Restricting Movement of Nursery Stock from California, Oregon, and Washington Nurseries" has required inspection of nurseries that ship hosts of P. ramorum outside the regulated areas. In 2004, an infected lilac was found in a nursery in New Jersey and in 2006 one was found in Maine. Since lilacs are popular ornamentals it is important to recognize symptoms of the disease on a variety of cultivars. It may also be useful for plant breeders to know if there are sources of resistance. Finally, it makes sense to test other ornamentals or significant forest species in the Oleaceae for susceptibility. This paper describes symptoms on lilac and related plants in the Oleaceae (Forsythia, Fraxinus, Ligustrum and Abeliophyllum) and analyses their relative susceptibility. Lilacs varied somewhat in susceptibility, with Syringa x josiflexa 'James MacFarlane' showing no symptoms and S. x prestoniae 'Alexander's pink' very few, but most cultivars developed similar large dark leaf lesions and suffered defoliation of heavily infected leaves. Fraxinus and Ligustrum were somewhat less susceptible than lilacs. The pathogen could sometimes be isolated from buds, but twig die-back was not observed. One month after the roots of Syringa, Abeliophyllum, Forsythia, and Ligustrum were inoculated, roots remained asymptomatic, but the pathogen could be recovered from washed or surface-sterilized root pieces of all genera except Ligustrum. Technical Abstract: Lilac is a host of Phytophthora ramorum, the "sudden oak death" pathogen. This paper describes the symptoms on Lilac and related plants in the Oleaceae (Forsythia, Fraxinus, Ligustrum and Abeliophyllum) and analyses their relative susceptibility. Lilacs varied somewhat in susceptibility, with Syringa x josiflexa 'James MacFarlane' showing no symptoms and S. x prestoniae 'Alexander's pink' very few, but most cultivars developed similar large dark leaf lesions and suffered defoliation of some heavily infected leaves. Fraxinus, and Ligustrum were somewhat less susceptible than lilacs. The pathogen could sometimes be isolated from buds, but twig die-back was not observed. One month after the roots of Syringa, Abeliophyllum, Forsythia, and Ligustrum were inoculated, roots remained asymptomatic, but the pathogen could be recovered from washed or surface-sterilized root pieces of all genera except Ligustrum. |
