Fraser fir is one of the most popular Christmas tree species in the United States and is indigenous to isolated mountain tops at elevations between 1370 and 2037 m in southwestern Virginia, western North Carolina, and eastern Tennessee (Liu, 1971). Christmas tree plantations of this species are scattered throughout the southern Appalachian region where Christmas tree sales provide an important economic resource. In 2006, revenue from Christmas tree sales in North Carolina totaled $134 million (U.S. Department of Agriculture, Economic Research Services, 2007). Fraser fir is grown for its fragrance, soft dark green needles, strong branches, excellent needle retention, and natural Christmas tree shape (Frampton, 2001).
Phytophthora cinnamomi, the primary cause of phytophthora root rot, has spread rapidly throughout soils in western North Carolina causing large economic losses. Once a site is infested, the pathogen is nearly impossible to eradicate. Fraser fir seedlings can die within 2 or 3 weeks from infection (Benson et al., 1998). Thus, there is a large demand in the region for planting stock that is resistant to, or tolerant of, this pathogen. To ameliorate the impact of this disease, some Christmas tree growers in the region are grafting fraser fir onto rootstocks of more resistant fir (Abies Mill.) species. Grafting onto resistant rootstocks is a widely accepted method of managing phytophthora root rot (Hinesley and Frampton, 2002). In a controlled inoculation study (Benson et al., 1998), momi fir (A. firma Sieb. et Zucc.) was the most resistant species to P. cinnamomi. Although it is the favored Abies rootstock species for phytophthora resistance, it is not planted for Christmas tree production because it has undesirable sharp, prickly, light green needles and breaks bud early leaving it extremely susceptible to late frosts. Turkish fir (Abies bornmuelleriana) was less resistant than momi fir (Benson et al., 1998) but has desirable Christmas tree qualities. Furthermore, because momi fir transplants are in short supply most years (as was the case for this study), turkish fir is the next best rootstock choice.
Fraser fir is usually grafted in early spring (April), when the rootstock and scion are dormant, but this is a busy time for growers. The opportunity to graft at other times of the year, e.g., late summer or early fall, would allow Christmas tree growers more flexibility. The objectives of this investigation were to 1) compare success and growth of grafting fresh fraser fir scions onto turkish fir rootstocks during the traditional time of grafting (April) with eight biweekly grafting dates from mid-July through mid-October; 2) assess the effect of shade and irrigation treatments on graft success and growth; and 3) evaluate grafting (mid-July through mid-October) using dormant fraser fir scions collected during April and stored at –1 °C.
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