Response of Turkish and Trojan fir to Phytophthora cinnamomi and P. cryptogea

Abstract

ABSTRACTPhytophthora root rot, primarily caused by the oomycete Phytophthora cinnamomi, is a large problem for the Christmas tree industry in North Carolina. Fraser fir (Abies fraseri) has no known innate resistance to this pathogen while some exotic fir species, such as Trojan (Abies equi-trojani) and Turkish (Abies bornmuelleriana) fir display varying amounts of resistance. A Phytophthora-resistance screening trial was completed with 1600 seedlings from 12 Turkish and Trojan fir families and Fraser and momi fir (A. firma). Seedlings from each family or species were inoculated with each of eight Phytophthora isolates, six P. cinnamomi and two Phytophthora cryptogea, in an effort to describe variability in isolate aggressiveness. Mortality was assessed as percent shoot necrosis bi-weekly for 16 weeks. Overall, rankings of resistance in fir species confirmed previous single-isolate-based results; momi fir was the most resistant, followed by Turkish, Trojan, and Fraser fir. P. cinnamomi isolates were generally more aggressive than P. cryptogea isolates. The two P. cryptogea isolates resulted in 5.6% and 0.8% mortality on Turkish fir, and 10.9% and 6.7% mortality on Trojan fir, the first reported resistance screen of these host-pathogen combinations. Pearson’s correlation testing identified a high degree of correlation between most isolates and overall mean mortality. Turkish and Trojan fir families appear to possess resistance to Phytophthora species common in North Carolina.