Dreyfusia nordmannianae (silver fir adelges).

Several conifer aphids of the family Adelgidae were probably introduced on nursery stock from Asia to Europe in the nineteenth century on imported fir (Abies spp.) and most of them were unknown before reaching Europe (Kenis et al., 2007). D. nordmannianae was introduced in Europe in the 1840s on imported Nordmann fir (Abies nordmanniana) and moved onto a new host, the European silver fir, Abies alba, where it has since caused important damage on young silver fir trees and Nordmann fir plantations (Bejer, 1981; Nierhaus-Wunderwald and Forster, 1999; Kenis et al., 2007).

Susceptibility of Fraser, Canaan, and Nordmann Fir to Root Rot Incited by Phytophthora cactorum and Phytophthora drechsleri

The susceptibility of fraser fir (Abies fraseri), canaan fir (A. balsamea var. phanerolepis), and nordmann fir (A. nordmanniana) to phytophthora root rot (PRR) incited by Phytophthora cactorum or P. drechsleri was assessed in two experiments in central Pennsylvania. In an 8-week greenhouse study, seedlings and transplants growing in soilless substrate were inoculated with Phytophthora in flooded and non-flooded settings. In an 8-week outdoor study conducted in raised planting boxes filled with soil, transplants were inoculated with Phytophthora species in well-drained and poorly drained soil. Based on foliar disease ratings, mortality rates, and dry shoot and root weights, differences in susceptibility to P. cactorum and P. drechsleri existed between these true fir (Abies) species. Fraser fir was very susceptible to P. cactorum and P. drechsleri. Canaan fir had strong resistance to P. cactorum and P. drechsleri in well-drained settings but was susceptible in poorly drained settings. Nordmann fir had very strong resistance to P. cactorum and P. drechsleri in both well-drained and poorly drained settings.

Response to Selfing in Seed Set, Seedling Establishment and Nursery Growth Based on Controlled Crosses of Abies nordmanniana Clones

Nordmann fir (Abies nordmanniana) is used for production of high value Christmas trees in short rotation. Potentially all trees are intended to be sold - no thinnings are normally applied. A high proportion of saleable trees per ha is the main key to secure economic return to the growers. Consumers demand a symmetric and rather uniform tree and, dependent on local traditions, it should be more or less dense and narrow. In Denmark, breeding of Nordmann fir and establishment of seed orchards focus on seed supply and improved Christmas tree quality - aiming at adaption and a rather uniform ideotype Christmas tree. Benefits from employing rather few clones, to maximise gain and uniformity, may potentially be counteracted by increased selfing. The objective of this study was to quantify the effect of selfing on percentage of filled seed and nursery establishment of seedlings. Inbreeding depression was seen for filled seeds (40%), growth traits (5-17%), plus mortality and axial damage (5-12 percent units). Many selfed seedlings survive and develop into marketable seedlings, although with a depression in numbers of 23-37%, or 9-12 percent units. Nursery sorting procedures can only partially reduce the number of inbred seedlings in Nordmann fir. The large variation among clones in the response to selfing indicates that knowledge of the behaviour of selfed progeny from specific clones in ‘small number seed orchards’ is of practical interest. Trade-offs between increased gain by selection of few clones and a penalty paid for increased inbreeding need further studies during a full Christmas tree rotation.