Abstract
Grafting provides a means to clonally produce Fraser fir (Abies fraseri (Pursh) Poir.) Christmas trees that have desirable traits such as faster growth, greater crown density, increased pest resistance, or more desirable foliage attributes than seedling stock. Grafting Fraser fir to disease resistant rootstocks also provides a means to ameliorate the impact of root rot, predominantly caused by Phytophthora cinnamomi Rands. The influence of ortet age on growth and market value of grafts has not been studied for Fraser fir Christmas tree production. A field trial was established in 2004 near Independence, Virginia (USA), with the objectives of assessing (1) the effect of ortet age (stock plants = 6 to 8, 10 to 12, and 18 to 20 years) and (2) shearing regimes (fixed leader length versus variable leader length) on growth, quality, and market value of Fraser fir Christmas trees. Commercial height, Christmas tree grade (based on U. S. Dept. of Agric. standards), and net present value (US dollars) were assessed at the time of harvest. Cone damage to quality was rated after 8 years in the field. Scions from Fraser fir Christmas trees 2 m or taller produced grafts that expressed maturation, resulting in lower tree quality, heavier cone damage, and decreased market value compared to seedling stock. In contrast, the quality and market value of grafts was similar to that of seedlings when scions were collected from young Fraser fir Christmas trees. For Christmas tree production, scions should be collected from the upper whorls of trees no older than 2 to 3 years in the field (6 to 8 years from seed). The effect of age on Fraser fir clones varies so that pre-screening might identify some older selections suitable for use as scion donors. Fixed versus variable shearing regimes had little effect on tree value, although some individual clones responded better to one regime or the other.
Highlights
Fraser fir (Abies fraseri (Pursh) Poir.) is one of the most important Christmas tree species grown in the United States
After two growing seasons in the field, the height of seedling and control grafts was not affected by shearing treatment or ortet age (Table 1)
Scions from older Fraser fir Christmas trees produce grafts that express maturation resulting in lower quality USDA grades, increased cone damage, and decreased economic value compared to seedling stock
Summary
Fraser fir (Abies fraseri (Pursh) Poir.) is one of the most important Christmas tree species grown in the United States. While commercial plantations usually are established from transplants originating from seed, a small but increasing number of Christmas tree growers in the region have been experimenting with grafted planting stock. There are limitations, grafting currently is the vegetative propagation technique of most interest to Fraser fir Christmas tree growers in the eastern USA because it provides a means to Forests 2018, 9, 182; doi:10.3390/f9040182 www.mdpi.com/journal/forests. Forests 2018, 9, 182 ameliorate the impact of root rot, predominantly caused by Phytophthora cinnamomi Rands. This disease has seriously impacted many sites throughout the production region for Fraser fir.
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