of one ortet could range from 0% to 96%. Shoots from the highest and lowest crown positions did not set roots. Differences in rooting capabilities of shoots from 4-year-old ortets are of no practical significance (BENTZER 1988). The causes of reduced rooting capacity of shoots derived from upper parts of the crown include cell specialization and a high level of biosynthesis of cytokinins, withe are strong inhibitors of root development (BOLLMARK and ELIASSON 1990b).

8.2.9. Cutting size

VolnA and RADOSTA (1985,1987) failed to find an influence of the size of the cuttings (including the growth of shoots from the previous year) on the extent of rooting. However, cutting size exerts some influence on the quality of rooting and the final planting material. Larger cuttings develop larger root systems and exhibit greater growth after rooting. However, HAUCK (1987) noted that large-diameter cuttings did not set roots, thin cuttings died rapidly, and medium-diameter cuttings rooted the best. Cuttings of two- and three-year-old shoots with short annual growth increments died after two months. Nevertheless, in propagating ornamental varieties, cuttings of two-year-old wood are sometimes used, especially in the case of dwarf varieties (OSIECKA1989). The need to regenerate selected ortets quickly may necessitate the use of shoot fragments to produce cuttings (HAVMOLLER 1981). It is essential that the basal portion of the shoots have at least four side buds (KLEINSCHMIT et al. 1973).

8.2.10. Population and individual variation

In large-scale propagation of selected clones, it was found that clones differ, sometimes widely, in their rooting capabilities (KLEINSCHMIT et al. 1973; TOMKOVA et al. 1987; CHLEPKO and TOMKOVA 1990; JANSON 1990) and development of root systems (TOMKOVA et al. 1987; CHLEPKO and TOMKOVA 1990). JOHNSEN (1986) observed significant variation and complex interactions of the mean number of roots between families, types of cuttings, and auxin treatment, which made the assessment of genetic factors difficult. SKR0PPA and DIETRICHSON (1986a) determined variance components for individual sources of variation in two groups of controlled crosses as follows: paternal variances of 15% and 1%; 14% and 13% for families (within paternal lines); 12% and 36% for clones within families; and 59% and 50% for environmental variance components. Hence, genetic factors comprised 41% and 50% of the total variance. Rooting repeatability amounted to 0.30 and 0.59 for clones within families and 0.89 and 0.85 in the case of family means. The heritability of rooting in cuttings ranged from 0.38 to 0.75, as determined by MERGEN (1960, after GIERTYCH 1977).

8.2.11. Growth after outplanting

Growth depends on genetic potential, ortet developmental stage, quality of the root system, and vigor (FOSTER et al. 1987). Cuttings with terminal buds develop plants with a reduced height increment, fewer forks, and a higher proportion of plagiotropic trees in comparison with cuttings developed from basal shoots lacking terminal buds (HAVMOLLER 1981). The fewest number of plagiotropic plants is derived from shoots obtained from the highest whorl (BENTZER1988). Trees of vegetative origin derived from young ortets initially grow faster than cuttings (KLEINSCHMIT and SCHMIDT 1977; Hartig 1986, ZDARSKA1988; KlIma 1990; GEMMEL et al. 1991). KLEINSCHMIT (1974) suggests outplanting propagated material on plantations as long as the ortet age does not exceed 20 years, even though ROULUND (1974) reported reduced growth of trees derived from 9-year-old ortets compared to plants of seed origin. With increasing age, the growth of trees of vegetative origin catches up with that of trees of seed origin, if genetic variability is disregarded (ROULUND 1974; KLEINSCHMIT and SCHMIDT 1977; Hartig 1986, ZdArskA 1988). The basic features of root systems of vegetatively propagated trees remain unchanged for at least 25 years after planting (KlIma 1990; Mauer and PAlat-KOVA 1994). Long-term observations of Picea abies trees of vegetative origin reveal that morphological differences, in relation to plants of seed origin, remain for decades, but that such trees are of full value and can be used in plantation forestry.

Wiadystaw Barzdajn, Agricultural University, Poznan.

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