Field Assessment of Turkish Fir (<i>Abies bornmuelleriana</i>) Resistance to Five Root-Rotting Phytophthora Species

Turkish fir (<i>Abies bornmuelleriana</i>) has been evaluated as a Phytophthora root rot (PRR)-resistant alternative to other PRR-susceptible <i>Abies</i> Christmas tree species. Although Turkish fir survival under heavy PRR disease pressure exceeds that of other host species, previous research has suggested that there may be variability in resistance owing to pedigree, ambient environment, and <i>Phytophthora</i> species. To assess differences in PRR survival in the field, 36 open-pollinated families of Turkish fir were challenged with a mixture of five species of <i>Phytophthora</i> under conditions conducive for disease. Seedlings were grown from seed that was gathered during a provenance collection effort from three provinces in Turkey. At the collection locations in each province, mother trees were located along an altitudinal gradient. The goals for this study included determining Turkish fir resistance in comparison with susceptible fir species, evaluating phenotype among Turkish fir families, assessing whether differences in phenotypes could be attributable to source location or elevation, determining whether source province or elevation influenced mortality, and comparing recovery of the five <i>Phytophthora</i> species used as inoculum. Turkish fir was demonstrated to be more resistant than noble fir (<i>A. procera</i>) or Fraser fir (<i>A. fraseri</i>) under the experimental conditions. Among the 36 Turkish fir families, 6 had a significantly lower probability of PRR mortality compared with all other families; half of these families were from the Karabük province. Similarly, Karabük province had the lowest overall mortality when family mortality proportions were totaled and compared among provinces. Evaluation of mortality among families from higher elevation sites within a province showed reduced mortality in comparison with middle and lower elevation sites, with variation among seed sources from different provinces. Among the five species of <i>Phytophthora</i> bulked for inoculum, <i>P. cryptogea</i> was the predominant species recovered from dead seedlings in both years. Results suggest that Turkish fir may be a viable PRR-resistant option for utilization in the Christmas tree industry despite some variability in phenotype among family.