Susceptibility of Some Lilac Cultivars and Other Members of the Oleaceae to Phytophthora ramorum

Lilac is a host of Phytophthora ramorum, but differences in host susceptibility of lilac cultivars and related genera have not been fully studied. This paper describes the symptoms on lilac and some other plants in the Oleaceae (Forsythia, Fraxinus, Ligustrum, and Abeliophyllum) and analyzes their relative susceptibility. Lilacs varied somewhat in susceptibility, with Syringa × josiflexa ‘ James MacFarlane’ showing no symptoms and S. × prestoniae ‘ Alexander's pink’ very few, but most cultivars developed large dark leaf lesions and suffered defoliation of heavily infected leaves. Fraxinus and Ligustrum were somewhat less susceptible than most lilac cultivars. 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 surfacesterilized root pieces of all genera tested except Ligustrum. Accepted for publication 18 July 2007. Published 1 November 2007.