Intergeneric Grafting of Ornamental Incense Cedar: First Results

Vegetative propagation is an important tool in both ornamental and forest tree improvement [1]. Grafting, an ancient agricultural and vegetative propagation technique, generally involves connecting two plant segments, a portion of shoot (‗scion‘) and a root piece (‗rootstock‘) [2]. It is most commonly employed in woody perennial crops to indirectly manipulate scion phenotype. A wide range of classical grafting techniques can be found in Garner [3]. Among these, bark grafting is relatively easy and very successful; it can be performed in the spring, only when the bark slips or separates easily from the wood. Taxonomic proximity is a general requirement for successful graft-take and long-term survival of the composite plant [4]. Rootstocks are usually from the same species as the scion, although some interspecific graft combinations have been successful. Grafting is widely used to propagate conifers [5] because many species are hard to root, especially when using cuttings from mature trees [6]. In general, only few species can be grafted: i.e. dwarf conifers, which cannot be successfully cloned using cuttings [7]. For conifers, grafters have historically used the following combinations: Picea abies for all spruces, and Pinus sylvestris for all two-needled and some three-needled pines [8]. Vuksani et al. [9] showed that the grafting compatibility of Arizona cypress plants and Mediterranean cypress rootstock was 87% in Category A (perfect union). The Cupressaceae family includes 21 genera and around 130 species of anemophilous trees and shrubs from the northern and southern hemispheres [10 and 11]. In the Mediterranean region, this family is widely represented both by native species, typically in woodlands, and by non-native species used for ornamental purposes and in reforestation programs. Albania is very rich in terms of flora: it is estimated that there are around 3,200 species of vascular plants, and the Cupressaceae family is quite widespread. Incense cedar (Calocedrus decurrens (Torr.) Florins) is the only example of the small genus Calocedrus [12], (syn. Libocedrus decurrens Torr.). It belongs to the Cupressaceae family native to western North America, with the bulk of its range in the United States, from central western Oregon through most of California and the extreme west of Nevada. It grows at altitudes of 50-2,900 m.

Incense cedar was recently introduced in Albania as an ornamental tree in public and private urban green spaces and is now much in demand [13].

Its foliage is produced in flattened sprays with scale-like leaves 2–15 mm long; they are arranged in opposing decussate pairs, the successive pairs spaced at increasing distances; the facial pairs are flat, while the lateral pairs fold over their bases [14]. As an ornamental plant, 'Aureovariegata' is a broadly columnar, evergreen, coniferous tree with exfoliating, red-brown to grey-green bark, slightly fragrant, flat sprays of linear, glossy, dark green and golden-yellow variegated leaves and, occasionally, erect, oval, red-brown female cones. Common propagation methods are seed and semi-hardwood cuttings. Geographic variability in cone and seed production is great. There is considerable information available on incense cedar seedling production. Although a prolific seed bearer, it does not produce seeds every year; germination under controlled conditions may reach 98%, but usually averages from 20 to 40% [15].

Although incense cedar does not reproduce vegetatively in nature, it can be stimulated to do so in a nursery greenhouse: rooting, assessed in spring, is best (92% rooting) with 2500 p.p.m. NAA [16]. Chamaecyparis lawsoniana scion graft success is moderate with C. decurrens; there is little information regarding incense cedar grafting on rootstocks of other genera. Research was, therefore, carried out to evaluate the effects of intergeneric grafting on the quality of ornamental incense cedar, which is little known in Albania.