Norway spruce will naturally layer and the resulting shoots can be used for propagation (RUBTSOV1952). However, this technique is not widely used because it is difficult and the success rates are rather low. Aerial layers are recommended for propagating valuable or endangered ortets. The rooting medium is peat moss (Sphagnum sp.) saturated with water, which is used to wrap the base of the layered shoot. To prevent drying, the peat moss is covered tightly with plastic wrap and with aluminium foil to protect against overheating. Placing several incisions in the shoot and treating with auxins will stimulate rooting. Layering is recommended for P. abies and P. pungens in April before bud burst. The shoots should be cut in a 2-3 mm ring and treated with a growth stimulator containing up to 0.5% IBA.
It is difficult to establish the origin of this method of propagation. Kleinschmit et al. (1973) quote PFIFFERLING'S reports (1830) about successful rooting of Picea abies cuttings. KURDIANI (1908) propagated 11 species of trees in a hotbed and obtained 84% rooting effectiveness for P. abies. Therefore, this tree species is not particularly difficult to propagate (KOBENDZA 1922). Today the propagation technique by cuttings is used in tree breeding and commercial production of selected planting material and ornamental plants as well as in the protection of genetic resources in situ.
Norway spruce cuttings are rooted with needles and should be exposed to light throughout the rooting period. Cuttings are placed directly into the substrate to a depth of about 2 cm. Appropriate controlled-environment facilities that provide heating and watering are helpful (LEPISTO 1974). KLEINSCHMIT et al. (1973) recommended setting the rooted cuttings in April and May, when air temperatures range from 5 to 30oC, whereas LEPISTO (1974) recommended temperatures of 20-25oC during the day and 10-15°C at night. DORMLING et al. (1977) and DORMLING and KELLERSTAM (1981) applied air temperatures of 17 to 18oC and lighting of 7-8 klx intensity for 18 h a day. Substrate heating is only recommended when rooting is conducted in winter (DEUBER and FARRAR 1940; LEPISTO 1974), whereas in spring and summer it is likely detrimental (KLEINSCHMIT 1972a, b). Shading, ventilation, and water are essential during summer when overheating may occur (RADOSTA 1987; VolnA et al. 1990) and it becomes important to prevent drying (HARTIG 1986). High humidity encourages the development of fungal diseases, in particular, grey mold (Botrytis cinerea); however, fungal diseases can be prevented by appropriate ventilation or use of fungicides such as captan and benomyl (KLEINSCHMIT et al. 1973; WUHLISCH 1984).
Standard substrates used for seedling rooting are blended mixtures of sand and fine peat most commonly at a 1:1 ratio. When automatic sprinkling is unavailable, the proportion of fine peat in the mixture is often increased. Perlite and vermiculite are frequent supplements (HRYNKIEWICZ-SUDNIK et al. 1991). P. abies cuttings are sensitive to rooting in different substrates (KLEIN-SCHMIT et al. 1973). Presumably, rooting conditions can influence the effectiveness of the various substrates. KLEINSCHMIT et al. (1973) recommended the exclusive use of pure gravel with a grain diameter ranging from 3-7 mm. Alternatively, LEPISTO (1974) advises the application of peat moss or a mixture of peat moss and garden peat. BENTZER (1985) considers a mixture of peat and perlite a useful potting medium for rooting. Skolek (1987) recommends an all-purpose substrate made up of a mixture of gravel and perlite (1:1). VolnA et al. (1990) recorded the best results in pure sand. Other authors recommend a 1:1 mixture of peat and vermiculite (ARMSON et al. 1980). Other media include the use of a mixture of sand and humus from forest stands (PELKONEN 1981), compost (KLEINSCHMIT 1972a), bark compost and sand (KosuliC 1984), blocks of mineral wool (JOHNSEN et al. 1985) as well as other mixtures. Substrate reaction (pH) has no clear effect on rooting (LAR-SEN 1946; KLEINSCHMIT et al. 1973).
Growth stimulators commonly include the auxins IAA, IBA, NAA as well as their salts. The effect of auxins can be enhanced by rooting co-factors (LIPECKI and Dennis 1970) or by a rhizocaline complex (MICHNIEWICZ 1969). Sometimes they are added to commercial preparations together with fungicides (most often Captan and Benomyl). The three most common methods of treating the base of the cuttings with stimulators are: 1) soaking in water-based solutions (0.01 - 0.1%) for 8 to 48 hours; 2) soaking in alcohol-based solutions (0.1 - 2%) for several seconds (quick dip method); and 3) dusting with talc powder containing from 0.1 to 2% auxins often mixed with co-factors and fungicides. Root stimulating activity has also been shown for secretions of my-corrhizal fungi, e.g. Laccaria laccata (SCOP. ex Fr.) Bk. et Br (CHMELIKOVA and CUDLIN 1990).
Growth stimulators generally must not come into contact with needles, as they may be toxic at the above-mentioned concentrations. The preparations should be selected to suit individual seedling types. Stimulators usually increase the proportion of successfully rooted cuttings and nearly always improve the quality of the root system. LARSEN (1946) claims that the positive impact of IAA is evident only in optimal outdoor conditions. Despite the frequent application of auxins in the propagation of P. abies, there are few direct comparative studies. DEUBER and Farrar (1940) observed only a negative effect of auxin IBA on rooting. PAULE and Skolek (1983) rooted cuttings from 1- and 2-year-old spruce trees using powdered forms of IAA (0.5% and 1%), IBA (0.5% and 1%) as well as the AS-1 preparation and observed either no effect or reduced rooting. In contrast, MEDEDOVIC (1987), using 0.125% IAA, reported increased rooting of shoots of 4-year-old ortets from 80 to 96% and from 10 to 60% in 12-year old trees. IAA potash salt (IAK) at 0.25% concentration improved rooting in shoots from 12-16-year-old trees from about 40 to 90%. JOHNSEN (1986) observed interactions between the action of auxin and the type of cuttings. KLEINSCHMIT et al. (1973) recommend the application of 0.1% IAK preparations. The use of auxin preparations for rooting is banned in Sweden (BENTZER 1985) and discouraged by LEPISTÖ (1974). Despite this, the above-mentioned authors report a very high success of rooting of P. abies shoots on a commercial production scale. Therefore, it is very likely unnecessary to treat P. abies cuttings with an exogenous auxin.
8.2.6. Age of maternal plants (cyclophysis)
With increasing age of the ortet, the capability of cuttings to develop roots decreases; they tend to develop poorer root systems and maintain plagiotropic and slow growth longer after rooting (ROULUND 1975, 1979; KLEINSCHMIT 1972a, b, 1992; JESTÄDT 1980; SCHACHLER and MATSCHKE1984; WÜHLISCH 1984; MEDEDOVIC 1987). Commercial propagation requires cuttings not older than 4 years and developed either from seeds or vegetatively. In this case, rooting success may approach 100%. Progenies of plus trees are frequently selected for cuttings (KLEINSCHMIT et al. 1973; KLEINSCHMIT 1974; LEPISTÖ 1974; BENTZER 1985; JOHNSEN 1985,1986; Werner and PETTERSSON 1981; VOLNÄ et al. 1990). DEUBER and Farrar (1940), EWALD and SCHACHLER (1990), and JANSON (1990) report the rooting of cuttings from mature trees. However, progeny derived from older ortets require more time to attain proper form and growth characteristics (BENTZER 1988; Dekker-Robert-SON and KLEINSCHMIT 1991; KLEINSCHMIT 1992).
One of the ways to overcome age effects (cyclophysis) is to use serial propagation. Rejuvenation is achieved by grafting (FRÖHLICH 1961) or micro-grafting (Ewald and Schachler 1990; Ewald et al. 1991). However, EWALD et al. (1991) failed rejuvinate P. abies micro-grafts, but did in the case of Larix europaea. DORMLING and KELLERSTAM (1981) recommend rejuvenation of maternal plants using a system of treatments comprised of controlled-environ-ments, cutting, and grafting. Treatment of ortets with cytokinins contributes to partial rejuvenation of P. abies clones, recognized by reduced flowering and an increased rooting capability (BOURIQUET et al. 1985; MATSCHKE et al. 1991). O-vaniline applied externally was effective in shoot rejuvenation (EWALD and SCHACHLER 1990). Serial propogation of young ortets used in tree breeding and clonal forestry prevents clone-aging effects (CLAIR et al. 1985; DEKKER-ROBERTSON and KLEINSCHMIT 1991).
8.2.7. Timing of shoot collection and planting cuttings
There is a strong effect of the time of year on the rooting ability of cut shoots. The optimal time is when shoot growth has fully ceased (GIROUARD 1975). Deuber and Farrar (1940) found minimal rooting (18%) of plants harvested in October and maximal rooting (64%) of plants harvested in December. For ornamental plants, the recommend period for shoot harvesting and planting ranges from June to August (KRUSSMANN 1964; BARTELS 1982; SLASKI and S^KOWSKI 1988; OSIECKA 1989; HRYNKIEWICZ-SUDNIK et al. 1991). In clonal nurseries of P. abies, a variety of combinations of harvesting and planting are possible in practice. The combinations include: shoot collection in November and rooting in winter or the following spring (LEPISTO 1974), shoot harvesting in January and rooting in May or shoot collection in late February or March (or up to May) followed by direct rooting (Kleinschmit et al. 1973; BENTZER 1985). It is not recommended to harvest the shoots in spring, since the shoots may exhibit winter frost damage (FREIJ 1986). Ideally, shoots should be harvested in the autumn when winter dormant. Rooting carried out from August until the middle of September gives very good results (FREIJ 1986). Spring rooting of shoots harvested in autumn requires cold storage in plastic bags at temperatures ranging from 4 to -5oC among various studies (KLEINSCHMIT et al. 1973; LEPISTO 1974; FREIJ 1986; BEHRENS 1987; Werner and PETTERSSON 1981). Short-term storage of cuttings wrapped in peat moss can be accomplished in galvanized boxes in an un-heated basement or shaded place outdoors (KLEINSCHMIT et al. 1973; JESTAEDT and RAPP1977). Cultivation of maternal plants under growth chamber conditions and rooting them in air-conditioned glasshouses may permit propagation in5-6 week rooting intervals and rapid regeneration of selected clones (JOHNSEN 1985).
The crown position from which shoots are harvested can affect rooting and subsequent growth. Position effects can be greater in older ortets (KLEINSCHMIT et al. 1973; GIROUARD 1974). Lateral shoots of 2- or 3-month-old cuttings root earlier in comparison with axial and dominant shoots, but develop fewer first-order roots (JOHNSEN 1986). VolnA and RADOSTA (1985) recorded better rooting of cuttings derived from the tops of axial shoots (in the second-year ortets) than from cuttings obtained from the base of axial shoots and sylleptic shoots. In studies carried out by ROULUND (1975), the rooting capability of P. abies shoots usually decreased with tree height. Hauck (1987), in experiments rooting shoots from grafts of plus trees, found slightly better rooting in second order than first order shoots, although overall rooting was poor. Hauck and VolnA (1990) showed that rooting capability of different shoots
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